Java8|Java8 Collections.sort()及Arrays.sort()中Lambda表达式及增强版Comparator的使用

本文主要介绍Java8 中Arrays.sort()及Collections.sort()中Lambda表达式及增强版Comparator的使用。 【Java8|Java8 Collections.sort()及Arrays.sort()中Lambda表达式及增强版Comparator的使用】作者:石头成说
来源:CSDN
原文:https://blog.csdn.net/qq_27127145/article/details/83930498
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import com.google.common.collect.Lists; import org.junit.Assert; import org.junit.Test; import java.util.Arrays; import java.util.Collections; import java.util.Comparator; import java.util.List; public class ComparatorTest { @Test public void test1(){ /** * Collections.sort()使用 */ //被排序的集合 List userList = Lists.newArrayList(new User("Jack",11),new User("Jack",10)); //1. Java8之前,使用匿名内部类的基本排序 Collections.sort(userList, new Comparator() { @Override public int compare(User user1, User user2) { return user1.getAge().compareTo(user2.getAge()); } }); //2. Java8,使用Lambda表达式的基本排序 Collections.sort(userList, (User user1, User user2) ->user1.getAge().compareTo(user2.getAge())); //userList.sort((User user1, User user2) -> user1.getAge().compareTo(user2.getAge())); //3. Java8,Lambda表达式可以简化,省略定义类型User userList.sort((user1, user2) -> user1.getAge().compareTo(user2.getAge())); //4. Java8,Lambda表达式,多条件排序 userList.sort((user1, user2) -> { if (user1.getName().equals(user2.getName())) { return user1.getAge() - user2.getAge(); } else { return user1.getName().compareTo(user2.getName()); } }); //5. Java8,多条件组合排序 userList.sort(Comparator.comparing(User::getName).thenComparing(User::getAge)); //6. Java8,提取Comparator进行排序 Collections.sort(userList, Comparator.comparing(User::getName)); //7. Java8,自定义静态的比较方法来排序(静态方法必须写在被比较的类(这里是User类)中) userList.sort(User::compareByAgeThenName); //8. Java8,反转排序 Comparator comparator = (user1, user2) -> user1.getName().compareTo(user2.getName()); userList.sort(comparator); //先按name排序 userList.sort(comparator.reversed()); //反转排序 Assert.assertEquals(userList.get(0),new User("Jack",10)); /** * Arrays.sort()使用 */ //被排序的字符串数组 String[] months = {"January","February","March","April","May","June","July","August","September","October","December"}; //按字符串长度排序 //1. Arrays.sort(months, (a, b) -> Integer.signum(a.length() - b.length())); //2. Arrays.sort(months, Comparator.comparingInt(String::length)); //3. Arrays.sort(months, (a, b) -> a.length() - b.length()); //4. Arrays.sort(months, (String a, String b) -> { return Integer.signum(a.length() - b.length()); } ); System.out.println(Arrays.toString(months)); } }

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