Java中Comparator的使用

在某些特殊情况，我们需要对一个对象数组或集合依照对应的属性排序；此时，我们就可以用Comparator接口处理。

上代码

TestComparaTo 类

 package com.test.interfacetest;

 public class TestComparaTo implements Comparable<TestComparaTo>{
  private int id;
  private String name;

  public int getId() {
   return id;
  }

  public void setId(int id) {
   this.id = id;
  }

  public String getName() {
   return name;
  }

  public void setName(String name) {
   this.name = name;
  }

  @Override
  public int compareTo(TestComparaTo o) {
   return Integer.compare(id, o.getId());
  }

 }

MainClass类

 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;

 import com.test.interfacetest.TestComparaTo;

 public class MainClass {

  public static void main(String[] args) {
   TestComparaTo testComparaTo = new TestComparaTo();
   testComparaTo.setId(21);
   testComparaTo.setName("钻石王老五");

   TestComparaTo testComparaTo1 = new TestComparaTo();
   testComparaTo1.setId(15);
   testComparaTo1.setName("岛市老八");

   TestComparaTo testComparaTo2 = new TestComparaTo();
   testComparaTo2.setId(19);
   testComparaTo2.setName("芜湖大司马");

   TestComparaTo[] s = {testComparaTo,testComparaTo1,testComparaTo2};
   List<TestComparaTo> asList = Arrays.asList(s);

   System.out.println("排序前集合内容：");
   for(TestComparaTo obj : asList) {
    System.out.println(obj.getName()+"id为："+obj.getId());
   }

   System.out.println("排序前数组内容：");
   for(TestComparaTo obj : s) {
    System.out.println(obj.getName()+"id为："+obj.getId());
   }

   Arrays.sort(s);
   Collections.sort(asList);

   System.out.println("排序后集合内容：");
   for(TestComparaTo obj : asList) {
    System.out.println(obj.getName()+"id为："+obj.getId());
   }
   System.out.println("排序后数组内容：");
   for(TestComparaTo obj : s) {
    System.out.println(obj.getName()+"id为："+obj.getId());
   }

  }

 }

总结就是：实现comparable接口的comparaTo方法，然后数组用Array的sort方法排序，集合用collection的sort方法排序。

在Java8后，可以运用lambda表达式使得Comparator使用起来更简单

例如下面四种方法

 //以下第一个参数a、b、c、d是TestComparaTo类的实例化对象的数组，对该数组排序

 //根据TestComparaTo类的name属性排序
 Arrays.sort(a,Comparator.comparing(TestComparaTo::getName)); 

 //如果name相同则根据id排序
 Arrays.sort(b,Comparator.comparing(TestComparaTo::getName).thenComparing(TestComparaTo::getId));

 //根据name长度排序
 Arrays.sort(c,Comparator.comparing(TestComparaTo::getName,(a,t)->Integer.compare(a.length(), t.length()))); 

  //根据name长度排序  显然这个比上一个更简单
 Arrays.sort(d,Comparator.comparingInt(a -> a.getName().length()));