简介
Comparator是一个比较器接口，位于java.util包下，用于排序和比较。
代码举例
import java.util.*; /** * @author ：gongxr * @description：Comparator比较器 */ @Slf4j public class ComparatorDemo { public ListgetList() { List users = new ArrayList<>(); User user = new User("Tom", 22, "Street #1"); users.add(user); users.add(new User("Michael", 33, "Street #2")); users.add(new User("Lily", 25, "Street #3")); return users; } @Test public void testComparator() { List users = getList(); /*查询年龄最大的人*/ Optional max = users.stream().max(Comparator.comparing(User::getAge)); log.info("maxAge: " + max.get().toString()); /*名字最长的人*/ Optional max2 = users.stream().map(u -> u.getName()).max(Comparator.comparing(String::length)); log.info("maxStringLength: " + max2.get()); } /** * 排序 * 在List或数组中的对象如果没有实现Comparable接口时，那么就需要调用者为需要排序的数组或List设置一个Compartor， * Compartor的compare方法用来告诉代码应该怎么去比较两个实例，然后根据比较结果进行排序 */ class Dog { public int age; public String name; public Dog(int age, String name) { super(); this.age = age; this.name = name; } @Override public String toString() { return "Dog [age=" + age + ", name=" + name + "]"; } } @Test public void test1() { List list = new ArrayList<>(); list.add(new Dog(5, "DogA")); list.add(new Dog(6, "DogB")); list.add(new Dog(7, "DogC")); Collections.sort(list, new Comparator () { @Override public int compare(Dog o1, Dog o2) { return o2.age - o1.age; } }); System.out.println("给狗狗按照年龄倒序：" + list); Collections.sort(list, new Comparator () { @Override public int compare(Dog o1, Dog o2) { return o1.name.compareTo(o2.name); } }); System.out.println("给狗狗按名字字母顺序排序：" + list); } /** * 分组 * 使用Comparator和for循环处理列表，来进行分类；通过调用者实现Comparator接口的比较逻辑，来告诉程序应该怎么比较，通过比较之后得结果来进行分组。 * 下面例子中分别按照狗狗的颜色和体重级别两个维度来进行分组，因此分组的核心逻辑其实就是比较逻辑。 * 下面抽了一个工具方法：dividerList,第一个参数为需要处理的数据源，第二参数是分组时的比较逻辑。 */ class Apple { public String color; public int weight; public Apple(String color, int weight) { super(); this.color = color; this.weight = weight; } @Override public String toString() { return "Apple [color=" + color + ", weight=" + weight + "]"; } } /*按条件分组*/ public static List > divider(Collection
datas, Comparator super T> c) { List > result = new ArrayList
>(); for (T t : datas) { boolean isSameGroup = false; for (int j = 0; j < result.size(); j++) { if (c.compare(t, result.get(j).get(0)) == 0) { isSameGroup = true; result.get(j).add(t); break; } } if (!isSameGroup) { // 创建 List
innerList = new ArrayList (); result.add(innerList); innerList.add(t); } } return result; } @Test public void test2() { List list = new ArrayList<>(); list.add(new Apple("红", 205)); list.add(new Apple("红", 131)); list.add(new Apple("绿", 248)); list.add(new Apple("绿", 153)); list.add(new Apple("红", 332)); list.add(new Apple("黄", 119)); list.add(new Apple("黄", 224)); List > byColors = divider(list, new Comparator
() { @Override public int compare(Apple o1, Apple o2) { // 按颜色分组 return o1.color.compareTo(o2.color); } }); System.out.println("按颜色分组" + byColors); List > byWeight = divider(list, new Comparator
() { @Override public int compare(Apple o1, Apple o2) { // 按重量级 return (o1.weight / 100 == o2.weight / 100) ? 0 : 1; } }); System.out.println("按重量级分组" + byWeight); } }
Original: https://www.cnblogs.com/gongxr/p/14512100.html
Author: 星瑞
Title: Java之Comparator使用举例
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