1 导读
NullPointerException在开发过程中经常遇到,稍有不慎小BUG就出现了,如果避免这个问题呢,Optional就是专门解决这个问题的类,那么Optional如何使用呢?让我们一起探索一下吧!
2 源码解析
2.1 Optional定义
Optional类是Java8为了解决null值判断问题而创建的容器类,在java.util 下,使用Optional类可以避免显式的null值判断,避免null导致的NullPointerException。首先,Optional是一个容器,它可以保存类型T的值,也可以为null的容器对象。Optional容器只能存一个值。
2.2 Optional的属性
1)源码:
<span class="com">/**</span>
<span class="com"> * Common instance for {@code empty()}.</span>
<span class="com"> */</span>
<span class="kwd">private<span class="pln"> <span class="kwd">static<span class="pln"> <span class="kwd">final<span class="pln"> <span class="typ">Optional<span class="pun"><?><span class="pln"> EMPTY <span class="pun">=<span class="pln"> <span class="kwd">new<span class="pln"> <span class="typ">Optional<span class="pun"><>();</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="com">/**</span>
<span class="com"> * If non-null, the value; if null, indicates no value is present</span>
<span class="com"> */</span>
<span class="kwd">private<span class="pln"> <span class="kwd">final<span class="pln"> T value<span class="pun">;</span></span></span></span></span>
根据源码可以看到Optional有两个属性,一个是为空值准备的EMPTY和泛型值value;
2.3 Optional的方法
Optional除toString()、hashCode() 、equals()等Object的方法外,还包含以下方法。
2.3.1 私有构造方法
<span class="com">/**</span>
<span class="com"> * Constructs an empty instance.</span>
<span class="com"> *</span>
<span class="com"> * @implNote Generally only one empty instance, {@link Optional#EMPTY},</span>
<span class="com"> * should exist per VM.</span>
<span class="com"> */</span>
<span class="kwd">private<span class="pln"> <span class="typ">Optional<span class="pun">()<span class="pln"> <span class="pun">{</span></span></span></span></span></span>
<span class="pln"> <span class="kwd">this<span class="pun">.<span class="pln">value <span class="pun">=<span class="pln"> <span class="kwd">null<span class="pun">;</span></span></span></span></span></span></span></span>
<span class="pun">}</span>
<span class="com">/**</span>
<span class="com">* Constructs an instance with the value present.</span>
<span class="com">*</span>
<span class="com">* @param value the non-null value to be present</span>
<span class="com">* @throws NullPointerException if value is null</span>
<span class="com">*/</span>
<span class="kwd">private<span class="pln"> <span class="typ">Optional<span class="pun">(<span class="pln">T value<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">this<span class="pun">.<span class="pln">value <span class="pun">=<span class="pln"> <span class="typ">Objects<span class="pun">.<span class="pln">requireNonNull<span class="pun">(<span class="pln">value<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pun">}</span>
[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:5bbdd98a-2bb4-4106-8606-2624c1c9c045
[En]
[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:cc9e2ced-800c-4958-801a-b8e597b35a20
2.3.2 创建方法
1)源码
<span class="kwd">public<span class="pln"> <span class="kwd">static<span class="pun"><<span class="pln">T<span class="pun">><span class="pln"> <span class="typ">Optional<span class="pun"><<span class="pln">T<span class="pun">><span class="pln"> empty<span class="pun">()<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="lit">@SuppressWarnings<span class="pun">(<span class="str">"unchecked"<span class="pun">)</span></span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="pln">T<span class="pun">><span class="pln"> t <span class="pun">=<span class="pln"> <span class="pun">(<span class="typ">Optional<span class="pun"><<span class="pln">T<span class="pun">>)<span class="pln"> EMPTY<span class="pun">;</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> t<span class="pun">;</span></span></span></span>
<span class="pun">}</span>
<span class="kwd">public<span class="pln"> <span class="kwd">static<span class="pln"> <span class="pun"><<span class="pln">T<span class="pun">><span class="pln"> <span class="typ">Optional<span class="pun"><<span class="pln">T<span class="pun">><span class="pln"> of<span class="pun">(<span class="pln">T value<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> <span class="kwd">new<span class="pln"> <span class="typ">Optional<span class="pun"><>(<span class="pln">value<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pun">}</span>
<span class="kwd">public<span class="pln"> <span class="kwd">static<span class="pln"> <span class="pun"><<span class="pln">T<span class="pun">><span class="pln"> <span class="typ">Optional<span class="pun"><<span class="pln">T<span class="pun">><span class="pln"> ofNullable<span class="pun">(<span class="pln">T value<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> value <span class="pun">==<span class="pln"> <span class="kwd">null<span class="pln"> <span class="pun">?<span class="pln"> empty<span class="pun">()<span class="pln"> <span class="pun">:<span class="pln"> of<span class="pun">(<span class="pln">value<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pun">}</span>
2)方法说明
- empty(): 创建一个空的 Optional 实例
- of(T t) : 创建一个 Optional 实例,当 t为null时抛出异常
- ofNullable(T t): 创建一个 Optional 实例,但当 t为null时不会抛出异常,而是返回一个空的实例
3)测试代码
<span class="kwd">public<span class="pln"> <span class="kwd">static<span class="pln"> <span class="kwd">void<span class="pln"> main<span class="pun">(<span class="typ">String<span class="pun">[]<span class="pln"> args<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Integer<span class="pln"> value1 <span class="pun">=<span class="pln"> <span class="kwd">null<span class="pun">;</span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Integer<span class="pln"> value2 <span class="pun">=<span class="pln"> <span class="lit">1<span class="pun">;</span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">try<span class="pln"> <span class="pun">{</span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">Integer<span class="pun">><span class="pln"> optional1 <span class="pun">=<span class="pln"> <span class="typ">Optional<span class="pun">.<span class="pln">empty<span class="pun">();</span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1创建了"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}<span class="kwd">catch<span class="pln"> <span class="pun">(<span class="typ">Exception<span class="pln"> e<span class="pun">){</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1失败了"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pln"> <span class="kwd">try<span class="pln"> <span class="pun">{</span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">Integer<span class="pun">><span class="pln"> optional2 <span class="pun">=<span class="pln"> <span class="typ">Optional<span class="pun">.<span class="pln">of<span class="pun">(<span class="pln">value1<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2创建了"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}<span class="kwd">catch<span class="pln"> <span class="pun">(<span class="typ">Exception<span class="pln"> e<span class="pun">){</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2失败了"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pln"> <span class="kwd">try<span class="pln"> <span class="pun">{</span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">Integer<span class="pun">><span class="pln"> optional3 <span class="pun">=<span class="pln"> <span class="typ">Optional<span class="pun">.<span class="pln">ofNullable<span class="pun">(<span class="pln">value1<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional3创建了"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}<span class="kwd">catch<span class="pln"> <span class="pun">(<span class="typ">Exception<span class="pln"> e<span class="pun">){</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional3失败了"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pln"> <span class="kwd">try<span class="pln"> <span class="pun">{</span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">Integer<span class="pun">><span class="pln"> optional4 <span class="pun">=<span class="pln"> <span class="typ">Optional<span class="pun">.<span class="pln">of<span class="pun">(<span class="pln">value2<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional4创建了"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}<span class="kwd">catch<span class="pln"> <span class="pun">(<span class="typ">Exception<span class="pln"> e<span class="pun">){</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional4失败了"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pln"> <span class="kwd">try<span class="pln"> <span class="pun">{</span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">Integer<span class="pun">><span class="pln"> optional5 <span class="pun">=<span class="pln"> <span class="typ">Optional<span class="pun">.<span class="pln">ofNullable<span class="pun">(<span class="pln">value2<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional5创建了"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}<span class="kwd">catch<span class="pln"> <span class="pun">(<span class="typ">Exception<span class="pln"> e<span class="pun">){</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional5失败了"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pun">}</span>
4)运行结果
2.3.3 值获取方法
1)源码
<span class="kwd">public<span class="pln"> T get<span class="pun">()<span class="pln"> <span class="pun">{</span></span></span></span></span>
<span class="pln"> <span class="kwd">if<span class="pln"> <span class="pun">(<span class="pln">value <span class="pun">==<span class="pln"> <span class="kwd">null<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">throw<span class="pln"> <span class="kwd">new<span class="pln"> <span class="typ">NoSuchElementException<span class="pun">(<span class="str">"No value present"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> value<span class="pun">;</span></span></span></span>
<span class="pun">}</span>
2)方法说明
get(): 如果Optional不为空,则返回该Optional容器中的值,否则抛出NoSuchElementExceptio 。
3)测试代码
<span class="kwd">public<span class="pln"> <span class="kwd">static<span class="pln"> <span class="kwd">void<span class="pln"> main<span class="pun">(<span class="typ">String<span class="pun">[]<span class="pln"> args<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Integer<span class="pln"> value1 <span class="pun">=<span class="pln"> <span class="kwd">null<span class="pun">;</span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Integer<span class="pln"> value2 <span class="pun">=<span class="pln"> <span class="lit">1<span class="pun">;</span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">Integer<span class="pun">><span class="pln"> optional1 <span class="pun">=<span class="pln"> <span class="typ">Optional<span class="pun">.<span class="pln">ofNullable<span class="pun">(<span class="pln">value1<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">Integer<span class="pun">><span class="pln"> optional2 <span class="pun">=<span class="pln"> <span class="typ">Optional<span class="pun">.<span class="pln">of<span class="pun">(<span class="pln">value2<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">try<span class="pln"> <span class="pun">{</span></span></span></span>
<span class="pln"> <span class="typ">Integer<span class="pln"> result<span class="pun">=<span class="pln">optional1<span class="pun">.<span class="pln">get<span class="pun">();</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1的值是:"<span class="pun">+<span class="pln">result<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}<span class="kwd">catch<span class="pln"> <span class="pun">(<span class="typ">Exception<span class="pln"> e<span class="pun">){</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1的值获取失败,原因:"<span class="pun">+<span class="pln">e<span class="pun">.<span class="pln">getMessage<span class="pun">());</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pln"> <span class="kwd">try<span class="pln"> <span class="pun">{</span></span></span></span>
<span class="pln"> <span class="typ">Integer<span class="pln"> result<span class="pun">=<span class="pln">optional2<span class="pun">.<span class="pln">get<span class="pun">();</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2的值是:"<span class="pun">+<span class="pln">result<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}<span class="kwd">catch<span class="pln"> <span class="pun">(<span class="typ">Exception<span class="pln"> e<span class="pun">){</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2的值获取失败,原因:"<span class="pun">+<span class="pln">e<span class="pun">.<span class="pln">getMessage<span class="pun">());</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pun">}</span>
4)运行结果
2.3.4 判断方法
1)源码
<span class="kwd">public<span class="pln"> <span class="kwd">boolean<span class="pln"> isPresent<span class="pun">()<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> value <span class="pun">!=<span class="pln"> <span class="kwd">null<span class="pun">;</span></span></span></span></span></span></span>
<span class="pun">}</span>
<span class="kwd">public<span class="pln"> <span class="kwd">void<span class="pln"> ifPresent<span class="pun">(<span class="typ">Consumer<span class="pun"><?<span class="pln"> <span class="kwd">super<span class="pln"> T<span class="pun">><span class="pln"> consumer<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">if<span class="pln"> <span class="pun">(<span class="pln">value <span class="pun">!=<span class="pln"> <span class="kwd">null<span class="pun">)</span></span></span></span></span></span></span></span></span>
<span class="pln"> consumer<span class="pun">.<span class="pln">accept<span class="pun">(<span class="pln">value<span class="pun">);</span></span></span></span></span></span>
<span class="pun">}</span>
<span class="kwd">public<span class="pln"> T orElse<span class="pun">(<span class="pln">T other<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> value <span class="pun">!=<span class="pln"> <span class="kwd">null<span class="pln"> <span class="pun">?<span class="pln"> value <span class="pun">:<span class="pln"> other<span class="pun">;</span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="kwd">public<span class="pln"> T orElseGet<span class="pun">(<span class="typ">Supplier<span class="pun"><?<span class="pln"> <span class="kwd">extends<span class="pln"> T<span class="pun">><span class="pln"> other<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> value <span class="pun">!=<span class="pln"> <span class="kwd">null<span class="pln"> <span class="pun">?<span class="pln"> value <span class="pun">:<span class="pln"> other<span class="pun">.<span class="pln">get<span class="pun">();</span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pun">}</span>
<span class="kwd">public<span class="pln"> <span class="pun"><<span class="pln">X <span class="kwd">extends<span class="pln"> <span class="typ">Throwable<span class="pun">><span class="pln"> T orElseThrow<span class="pun">(<span class="typ">Supplier<span class="pun"><?<span class="pln"> <span class="kwd">extends<span class="pln"> X<span class="pun">><span class="pln"> exceptionSupplier<span class="pun">)<span class="pln"> <span class="kwd">throws<span class="pln"> X <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">if<span class="pln"> <span class="pun">(<span class="pln">value <span class="pun">!=<span class="pln"> <span class="kwd">null<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> value<span class="pun">;</span></span></span></span>
<span class="pln"> <span class="pun">}<span class="pln"> <span class="kwd">else<span class="pln"> <span class="pun">{</span></span></span></span></span></span>
<span class="pln"> <span class="kwd">throw<span class="pln"> exceptionSupplier<span class="pun">.<span class="pln">get<span class="pun">();</span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pun">}</span>
2)方法说明
- isPresent(): 判断optional是否为空,如果空则返回false,否则返回true
- ifPresent(Consumer c): 如果optional不为空,则将optional中的对象传给Comsumer函数
- orElse(T other): 如果optional不为空,则返回optional中的对象;如果为null,则返回 other 这个对象。
- orElseGet(Supplier other): 如果optional不为空,则返回optional中的对象;如果为null,否则调用其他函数并返回调用的结果
- orElseThrow(Supplier exception): 如果optional不为空,则返回optional中的对象;如果为null,则抛出Supplier函数生成的异常
3)测试代码
<span class="kwd">public<span class="pln"> <span class="kwd">static<span class="pln"> <span class="kwd">void<span class="pln"> main<span class="pun">(<span class="typ">String<span class="pun">[]<span class="pln"> args<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Integer<span class="pln"> value1 <span class="pun">=<span class="pln"> <span class="kwd">null<span class="pun">;</span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Integer<span class="pln"> value2 <span class="pun">=<span class="pln"> <span class="lit">1<span class="pun">;</span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">Integer<span class="pun">><span class="pln"> optional1 <span class="pun">=<span class="pln"> <span class="typ">Optional<span class="pun">.<span class="pln">ofNullable<span class="pun">(<span class="pln">value1<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">Integer<span class="pun">><span class="pln"> optional2 <span class="pun">=<span class="pln"> <span class="typ">Optional<span class="pun">.<span class="pln">of<span class="pun">(<span class="pln">value2<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">try<span class="pln"> <span class="pun">{</span></span></span></span>
<span class="pln"> <span class="kwd">if<span class="pun">(<span class="pln">optional1<span class="pun">.<span class="pln">isPresent<span class="pun">()){</span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1的isPresent结果不为空"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}<span class="kwd">else<span class="pun">{</span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1的isPresent结果为空"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pln"> <span class="pun">}<span class="kwd">catch<span class="pln"> <span class="pun">(<span class="typ">Exception<span class="pln"> e<span class="pun">){</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1的isPresent判空失败,原因:"<span class="pun">+<span class="pln">e<span class="pun">.<span class="pln">getMessage<span class="pun">());</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pln"> <span class="kwd">try<span class="pln"> <span class="pun">{</span></span></span></span>
<span class="pln"> <span class="kwd">if<span class="pun">(<span class="pln">optional2<span class="pun">.<span class="pln">isPresent<span class="pun">()){</span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2的isPresent结果不为空"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}<span class="kwd">else<span class="pun">{</span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2的isPresent结果为空"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pln"> <span class="pun">}<span class="kwd">catch<span class="pln"> <span class="pun">(<span class="typ">Exception<span class="pln"> e<span class="pun">){</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2的isPresent判空失败,原因:"<span class="pun">+<span class="pln">e<span class="pun">.<span class="pln">getMessage<span class="pun">());</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pln"> optional1<span class="pun">.<span class="pln">ifPresent<span class="pun">(<span class="pln">t<span class="pun">->{</span></span></span></span></span></span>
<span class="pln"> <span class="kwd">int<span class="pln"> i <span class="pun">=<span class="pln">t<span class="pun">+<span class="lit">1<span class="pun">;</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1处理后的值是"<span class="pun">+<span class="pln">i<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">});</span></span>
<span class="pln"> optional2<span class="pun">.<span class="pln">ifPresent<span class="pun">(<span class="pln">t<span class="pun">->{</span></span></span></span></span></span>
<span class="pln"> <span class="kwd">int<span class="pln"> i <span class="pun">=<span class="pln">t<span class="pun">+<span class="lit">1<span class="pun">;</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2处理后的值是"<span class="pun">+<span class="pln">i<span class="pun">);});</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Integer<span class="pln"> value3 <span class="pun">=<span class="pln"> <span class="lit">2<span class="pun">;</span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Integer<span class="pln"> result <span class="pun">=<span class="pln"> optional1<span class="pun">.<span class="pln">orElse<span class="pun">(<span class="pln">value3<span class="pun">);</span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1执行orElse处理后的值是"<span class="pun">+<span class="pln">result<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> result <span class="pun">=<span class="pln"> optional2<span class="pun">.<span class="pln">orElse<span class="pun">(<span class="pln">value3<span class="pun">);</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2执行orElse处理后的值是"<span class="pun">+<span class="pln">result<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> result <span class="pun">=<span class="pln"> optional1<span class="pun">.<span class="pln">orElseGet<span class="pun">(()-><span class="pln"> <span class="kwd">new<span class="pln"> <span class="typ">Integer<span class="pun">(-<span class="lit">1<span class="pun">));</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1执行orElseGet处理后的值是"<span class="pun">+<span class="pln">result<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> result <span class="pun">=<span class="pln"> optional2<span class="pun">.<span class="pln">orElseGet<span class="pun">(()-><span class="pln"> <span class="kwd">new<span class="pln"> <span class="typ">Integer<span class="pun">(-<span class="lit">1<span class="pun">));</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2执行orElseGet处理后的值是"<span class="pun">+<span class="pln">result<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">try<span class="pln"> <span class="pun">{</span></span></span></span>
<span class="pln"> result <span class="pun">=<span class="pln"> optional1<span class="pun">.<span class="pln">orElseThrow <span class="pun">(()-><span class="pln"> <span class="kwd">new<span class="pln"> <span class="typ">RuntimeException<span class="pun">(<span class="str">"值是空的"<span class="pun">));</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1执行orElseThrow处理后的值是"<span class="pun">+<span class="pln">result<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}<span class="kwd">catch<span class="pln"> <span class="pun">(<span class="typ">Exception<span class="pln"> e<span class="pun">){</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1的orElseThrow抛出异常:"<span class="pun">+<span class="pln">e<span class="pun">.<span class="pln">getMessage<span class="pun">());</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pln"> <span class="kwd">try<span class="pln"> <span class="pun">{</span></span></span></span>
<span class="pln"> result <span class="pun">=<span class="pln"> optional2<span class="pun">.<span class="pln">orElseThrow <span class="pun">(()-><span class="pln"> <span class="kwd">new<span class="pln"> <span class="typ">RuntimeException<span class="pun">(<span class="str">"值是空的"<span class="pun">));</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2执行orElseThrow处理后的值是"<span class="pun">+<span class="pln">result<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}<span class="kwd">catch<span class="pln"> <span class="pun">(<span class="typ">Exception<span class="pln"> e<span class="pun">){</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2的orElseThrow抛出异常:"<span class="pun">+<span class="pln">e<span class="pun">.<span class="pln">getMessage<span class="pun">());</span></span></span></span></span></span></span></span></span></span></span></span></span>
4)运行结果
2.3.5 过滤方法
1)源码
<span class="kwd">public<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="pln">T<span class="pun">><span class="pln"> filter<span class="pun">(<span class="typ">Predicate<span class="pun"><?<span class="pln"> <span class="kwd">super<span class="pln"> T<span class="pun">><span class="pln"> predicate<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Objects<span class="pun">.<span class="pln">requireNonNull<span class="pun">(<span class="pln">predicate<span class="pun">);</span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">if<span class="pln"> <span class="pun">(!<span class="pln">isPresent<span class="pun">())</span></span></span></span></span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> <span class="kwd">this<span class="pun">;</span></span></span></span></span>
<span class="pln"> <span class="kwd">else</span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> predicate<span class="pun">.<span class="pln">test<span class="pun">(<span class="pln">value<span class="pun">)<span class="pln"> <span class="pun">?<span class="pln"> <span class="kwd">this<span class="pln"> <span class="pun">:<span class="pln"> empty<span class="pun">();</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pun">}</span>
2)方法说明
filter(Predicate p): 如果optional不为空,则执行Predicate p,如果p的结果为true,则返回原本的optional,否则返回空的optional
3)测试代码
<span class="kwd">public<span class="pln"> <span class="kwd">static<span class="pln"> <span class="kwd">void<span class="pln"> main<span class="pun">(<span class="typ">String<span class="pun">[]<span class="pln"> args<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Integer<span class="pln"> value1 <span class="pun">=<span class="pln"> <span class="lit">5<span class="pun">;</span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Integer<span class="pln"> value2 <span class="pun">=<span class="pln"> <span class="lit">6<span class="pun">;</span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">Integer<span class="pun">><span class="pln"> optional1 <span class="pun">=<span class="pln"> <span class="typ">Optional<span class="pun">.<span class="pln">ofNullable<span class="pun">(<span class="pln">value1<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">Integer<span class="pun">><span class="pln"> optional2 <span class="pun">=<span class="pln"> <span class="typ">Optional<span class="pun">.<span class="pln">of<span class="pun">(<span class="pln">value2<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">Integer<span class="pun">><span class="pln"> result <span class="pun">=<span class="pln">optional1<span class="pun">.<span class="pln">filter<span class="pun">(<span class="pln">t<span class="pun">-><span class="pln">t <span class="pun">><span class="pln"> <span class="lit">5<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1的filter后的值:"<span class="pun">+<span class="pln">result<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> result <span class="pun">=<span class="pln">optional2<span class="pun">.<span class="pln">filter<span class="pun">(<span class="pln">t<span class="pun">-><span class="pln">t <span class="pun">><span class="pln"> <span class="lit">5<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2的filter后的值:"<span class="pun">+<span class="pln">result<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
4)运行结果
2.3.6 映射方法
1)源码
<span class="kwd">public<span class="pun"><<span class="pln">U<span class="pun">><span class="pln"> <span class="typ">Optional<span class="pun"><<span class="pln">U<span class="pun">><span class="pln"> map<span class="pun">(<span class="typ">Function<span class="pun"><?<span class="pln"> <span class="kwd">super<span class="pln"> T<span class="pun">,<span class="pln"> <span class="pun">?<span class="pln"> <span class="kwd">extends<span class="pln"> U<span class="pun">><span class="pln"> mapper<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Objects<span class="pun">.<span class="pln">requireNonNull<span class="pun">(<span class="pln">mapper<span class="pun">);</span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">if<span class="pln"> <span class="pun">(!<span class="pln">isPresent<span class="pun">())</span></span></span></span></span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> empty<span class="pun">();</span></span></span></span>
<span class="pln"> <span class="kwd">else<span class="pln"> <span class="pun">{</span></span></span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> <span class="typ">Optional<span class="pun">.<span class="pln">ofNullable<span class="pun">(<span class="pln">mapper<span class="pun">.<span class="pln">apply<span class="pun">(<span class="pln">value<span class="pun">));</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pun">}</span>
<span class="kwd">public<span class="pun"><<span class="pln">U<span class="pun">><span class="pln"> <span class="typ">Optional<span class="pun"><<span class="pln">U<span class="pun">><span class="pln"> flatMap<span class="pun">(<span class="typ">Function<span class="pun"><?<span class="pln"> <span class="kwd">super<span class="pln"> T<span class="pun">,<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="pln">U<span class="pun">>><span class="pln"> mapper<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Objects<span class="pun">.<span class="pln">requireNonNull<span class="pun">(<span class="pln">mapper<span class="pun">);</span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">if<span class="pln"> <span class="pun">(!<span class="pln">isPresent<span class="pun">())</span></span></span></span></span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> empty<span class="pun">();</span></span></span></span>
<span class="pln"> <span class="kwd">else<span class="pln"> <span class="pun">{</span></span></span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> <span class="typ">Objects<span class="pun">.<span class="pln">requireNonNull<span class="pun">(<span class="pln">mapper<span class="pun">.<span class="pln">apply<span class="pun">(<span class="pln">value<span class="pun">));</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pun">}</span>
2)方法说明
- map(Function
- flatMap(Function< T,Optional> mapper): 如果有值,则对其应用提供的可选映射函数,返回结果,否则返回空的可选函数。 这个方法类似于map(Function),但是提供的映射器的结果已经是一个可选的,如果调用,flatMap不会用额外的可选的包装它。
- 区别:map会自动将u放到optional中,而flatMap则需要手动给u创建一个optional
3)测试代码
<span class="pln"> <span class="kwd">public<span class="pln"> <span class="kwd">static<span class="pln"> <span class="kwd">void<span class="pln"> main<span class="pun">(<span class="typ">String<span class="pun">[]<span class="pln"> args<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">User<span class="pln"> user1 <span class="pun">=<span class="pln"> <span class="kwd">null<span class="pun">;</span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">User<span class="pln"> user2 <span class="pun">=<span class="pln"> <span class="kwd">new<span class="pln"> <span class="typ">User<span class="pun">(<span class="str">"user2名字"<span class="pun">,<span class="lit">19<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">User<span class="pun">><span class="pln"> optional1 <span class="pun">=<span class="pln"> <span class="typ">Optional<span class="pun">.<span class="pln">ofNullable<span class="pun">(<span class="pln">user1<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">User<span class="pun">><span class="pln"> optional2 <span class="pun">=<span class="pln"> <span class="typ">Optional<span class="pun">.<span class="pln">of<span class="pun">(<span class="pln">user2<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"=========map=========="<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1的map前的值:"<span class="pun">+<span class="pln">optional1<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">String<span class="pun">><span class="pln"> result <span class="pun">=<span class="pln">optional1<span class="pun">.<span class="pln">map<span class="pun">(<span class="pln">t<span class="pun">-><span class="pln">t<span class="pun">.<span class="pln">getName<span class="pun">());</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1的map后的值:"<span class="pun">+<span class="pln">result<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2的map前的值:"<span class="pun">+<span class="pln">optional2<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> result <span class="pun">=<span class="pln">optional2<span class="pun">.<span class="pln">map<span class="pun">(<span class="pln">t<span class="pun">-><span class="pln">t<span class="pun">.<span class="pln">getName<span class="pun">());</span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2的map后的值:"<span class="pun">+<span class="pln">result<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"===========flatMap========"<span class="pun">);</span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1的flatMap前的值:"<span class="pun">+<span class="pln">optional1<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Optional<span class="pun"><<span class="typ">Integer<span class="pun">><span class="pln"> result2 <span class="pun">=<span class="pln">optional1<span class="pun">.<span class="pln">flatMap<span class="pun">(<span class="pln">t<span class="pun">-><span class="typ">Optional<span class="pun">.<span class="pln">ofNullable<span class="pun">(<span class="pln">t<span class="pun">.<span class="pln">getAge<span class="pun">()));</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional1的flatMap后的值:"<span class="pun">+<span class="pln">result2<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2的flatMap前的值:"<span class="pun">+<span class="pln">optional2<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> result2 <span class="pun">=<span class="pln">optional2<span class="pun">.<span class="pln">flatMap<span class="pun">(<span class="pln">t<span class="pun">-><span class="typ">Optional<span class="pun">.<span class="pln">ofNullable<span class="pun">(<span class="pln">t<span class="pun">.<span class="pln">getAge<span class="pun">()));</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">System<span class="pun">.<span class="pln">out<span class="pun">.<span class="pln">println<span class="pun">(<span class="str">"optional2的flatMap后的值:"<span class="pun">+<span class="pln">result2<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="kwd">public<span class="pln"> <span class="kwd">class<span class="pln"> <span class="typ">User<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">String<span class="pln"> name<span class="pun">;</span></span></span></span>
<span class="pln"> <span class="typ">Integer<span class="pln"> age<span class="pun">;</span></span></span></span>
<span class="pln"> <span class="kwd">public<span class="pln"> <span class="typ">User<span class="pun">(<span class="typ">String<span class="pln"> name<span class="pun">,<span class="typ">Integer<span class="pln"> age<span class="pun">){</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">this<span class="pun">.<span class="pln">name <span class="pun">=<span class="pln"> name<span class="pun">;</span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">this<span class="pun">.<span class="pln">age<span class="pun">=<span class="pln">age<span class="pun">;</span></span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pln"> <span class="kwd">public<span class="pln"> <span class="typ">String<span class="pln"> getName<span class="pun">()<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> name<span class="pun">;</span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pln"> <span class="kwd">public<span class="pln"> <span class="typ">Integer<span class="pln"> getAge<span class="pun">()<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">return<span class="pln"> age<span class="pun">;</span></span></span></span>
4)运行结果
3 应用实例
3.1 错误用法
- 由于Optional并没有实现Serializable接口,所以不能作为类的属性。
- 不要把Optional作为方法的参数。
- 把if(x!=null)直接换成Optional.ofNullable(x).isPresent(),这样有过度编码的嫌疑。
- 直接使用Optional.get()的返回值进行操作,String result =Optional.ofNullable(null).get().toString();这样还是会抛出异常的。
3.2 建议用法
A类有属性B类,B类有属性C类,C类有name这个字段。
使用Optional之前:
<span class="kwd">if<span class="pun">(<span class="pln">atest<span class="pun">!=<span class="kwd">null<span class="pun">){</span></span></span></span></span></span>
<span class="pln"> <span class="typ">Btest<span class="pln"> btest <span class="pun">=<span class="pln">atest<span class="pun">.<span class="pln">getBtest<span class="pun">();</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">if<span class="pun">(<span class="pln">btest<span class="pun">!=<span class="kwd">null<span class="pun">){</span></span></span></span></span></span></span>
<span class="pln"> <span class="typ">Ctest<span class="pln"> ctest <span class="pun">=<span class="pln"> btest<span class="pun">.<span class="pln">getCtest<span class="pun">();</span></span></span></span></span></span></span></span>
<span class="pln"> <span class="kwd">if<span class="pln"> <span class="pun">(<span class="pln">ctest <span class="pun">!=<span class="pln"> <span class="kwd">null<span class="pun">)<span class="pln"> <span class="pun">{</span></span></span></span></span></span></span></span></span></span></span>
<span class="pln"> name <span class="pun">=<span class="pln">ctest<span class="pun">.<span class="pln">getName<span class="pun">();</span></span></span></span></span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pln"> <span class="pun">}</span></span>
<span class="pun">}</span>
使用Optional之后:
<span class="pln">name <span class="pun">=<span class="pln"> <span class="typ">Optional<span class="pun">.<span class="pln">ofNullable<span class="pun">(<span class="pln">atest<span class="pun">).<span class="pln">map<span class="pun">(<span class="pln">t<span class="pun">-><span class="pln">t<span class="pun">.<span class="pln">getBtest<span class="pun">()).<span class="pln">map<span class="pun">(<span class="pln">t<span class="pun">-><span class="pln">t<span class="pun">.<span class="pln">getCtest<span class="pun">()).<span class="pln">map<span class="pun">(<span class="pln">t<span class="pun">-><span class="pln">t<span class="pun">.<span class="pln">getName<span class="pun">()).<span class="pln">orElse<span class="pun">(<span class="str">"默认值"<span class="pun">);</span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span>
[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:c8111f81-0de2-489e-a42c-7bf77bcc338b
[En]
[TencentCloudSDKException] code:FailedOperation.ServiceIsolate message:service is stopped due to arrears, please recharge your account in Tencent Cloud requestId:b605e03c-e8da-448a-8dc0-90975858c28d
4 总结
通过对Optional源码解析和用例测试代码的运行结果,可以看出使用Optional可以优化null值判断代码,让代码变得更加优雅和整洁。
自猿其说Tech-JDL京东物流技术与数据智能部
作者:陈昌浩
Original: https://www.cnblogs.com/Jcloud/p/16740664.html
Author: 京东云开发者
Title: Optional源码解析与实践
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