java比较器以及集合类实现排序

一、java实现比较有两种方式，分别是实现Comparable接口与实现Comparator接口两种方式

方式一：

实现Comparable 接口

package com.loan.entity;import lombok.Data;@Datapublic class Test implements Comparable<Test>{private int id;private String name;private int age;@Overridepublic int compareTo(Test o) {// TODO Auto-generated method stubreturn this.name.compareTo(o.getName());}public Test() {}public Test(int id, String name, int age) {this.id = id;this.name = name;this.age = age;}public static void main(String[] args) {Test test1=new Test(1,"aser1",20);Test test2=new Test(2,"aser1",30);int result=test1.compareTo(test2);String res=result>0?"test1>test2":"test2>test1";System.out.println(res);}}

方式二：实现Comparator接口，实现者被称为比较器，不同于Comparable的在于Comparator接口一般不会被集合元素类所实现，而是单独实现或者用匿名内部类方式实现

1、单独实现：

package com.loan.entity;import java.util.Comparator;import lombok.Data;@Datapublic class Test{private int id;private String name;private int age;public Test(){}public Test(int id, String name, int age) {this.id = id;this.name = name;this.age = age;}public static void main(String[] args) {Test test1=new Test(1,"aser1",20);Test test2=new Test(2,"aser1",30);//static访问成员内部类，必须先实例化外部类对象Comparator<Test> comp=new Test().new TestComparator();int result=comp.compare(test1,test2);System.out.println(result>0?"tes1>test2":"test1<test2");}class TestComparator implements Comparator<Test>{@Overridepublic int compare(Test o1, Test o2) {// TODO Auto-generated method stubreturn o1.getAge()-o2.getAge();}}}

匿名内部类实现：

package com.loan.entity;import java.util.Comparator;import lombok.Data;@Datapublic class Test{private int id;private String name;private int age;public Test(int id, String name, int age) {this.id = id;this.name = name;this.age = age;}public static void main(String[] args) {Test test1=new Test(1,"aser1",20);Test test2=new Test(2,"aser1",30);int result=new Comparator<Test>(){@Overridepublic int compare(Test o1, Test o2) {// TODO Auto-generated method stubreturn o1.getAge()-o2.getAge();}}.compare(test1, test2);System.out.println(result>0?"test1>test2":"test1<test2");}}

二、集合类实现排序

package com.loan.entity;import java.util.ArrayList;import java.util.Collection;import java.util.Collections;import java.util.Comparator;import java.util.List;import lombok.Data;@Datapublic class Test implements Comparable{private int id;private String name;private int age;public Test(){}public Test(int id, String name, int age) {this.id = id;this.name = name;this.age = age;}public static void main(String[] args) {Test test1=new Test(1,"user1",20);Test test2=new Test(2,"user2",10);Test test3=new Test(3,"user3",40);Test test4=new Test(4,"user4",30);List<Test> list=new ArrayList<Test>();list.add(test1);list.add(test2);list.add(test3);list.add(test4);String s="原来顺序:";for(Test test:list){s+=test.getName()+"_"+test.getAge()+"\t";}System.out.println(s);//要实现默认排序，必须实现Comparable接口，运用compareTo方法Collections.sort(list);String s1="默认排序：";for(Test test:list){s1+=test.getName()+"_"+test.getAge()+"\t";}System.out.println(s1);Comparator cmp=Collections.reverseOrder();Collections.sort(list, cmp);String s2="降序排序";for(Test test:list){s2+=test.getName()+"_"+test.getAge()+"\t";}System.out.println(s2);cmp=new Comparator<Test>(){@Overridepublic int compare(Test o1, Test o2) {// TODO Auto-generated method stubreturn o1.getId()-o2.getId();}};Collections.sort(list, cmp);String s3="自定义：";for(Test test:list){s3+=test.getName()+"_"+test.getAge()+"\t";}System.out.println(s3);}@Overridepublic int compareTo(Object o) {// TODO Auto-generated method stubreturn this.age-((Test)o).getAge();}}

运行结果：