Java集合排序（看完秒懂）

比如将一个List<Student>排序，则有两种方式：

1：Student实现Comparable接口：

2：给排序方法传递一个Comparator参数：

请看下面的举例：

Student类：

package demo;

//Student实现Comparable，需要实现compareTo方法
public class Student implements Comparable<Student>{
	private String name;
	private Integer age;

	public Student(String name,Integer age) {
		// TODO Auto-generated constructor stub
		this.name=name;
		this.age=age;
	}

	public String getName() {
		return name;
	}

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

	public Integer getAge() {
		return age;
	}

	public void setAge(Integer age) {
		this.age = age;
	}

	@Override
	public int compareTo(Student o) {
		// TODO Auto-generated method stub
		if(this.age>o.getAge()){
			return 1;
		}
		else if(this.age<o.getAge()){
			return -1;
		}
		else{
			return 0;
		}
	}
}

主类：

package demo;

import java.util.*;

public class main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		List<Student> list=new ArrayList<Student>();
		Student s1=new Student("T-F", 18);
		Student s2=new Student("H胡歌", 28);
		Student s3=new Student("Z周润发", 50);
		Student s4=new Student("M梅兰芳", 100);
		list.add(s1);
		list.add(s4);
		list.add(s3);
		list.add(s2);

		Iterator iterator=list.iterator();
		System.out.println("------默认排序（按年纪）-------");
		Collections.sort(list);
		while(iterator.hasNext()){
			Student s=(Student)iterator.next();
			System.out.println(s.getName()+" "+s.getAge());
		}

		System.out.println("------倒序排序-------");
		Comparator comparator=Collections.reverseOrder();
		Collections.sort(list,comparator);
		Iterator iterator_reverse=list.iterator();
		while(iterator_reverse.hasNext()){
			Student s=(Student)iterator_reverse.next();
			System.out.println(s.getName()+" "+s.getAge());
		}

		System.out.println("------根据姓名排序-------");
		Collections.sort(list,new Comparator<Student>(){
			@Override
			public int compare(Student o1, Student o2) {
				// TODO Auto-generated method stub
				return    o1.getName().compareTo(o2.getName());
			}}
		);
		Iterator iterator_name=list.iterator();
		while(iterator_name.hasNext()){
			Student s=(Student)iterator_name.next();
			System.out.println(s.getName()+" "+s.getAge());
		}

	}
}

执行结果：

------默认排序-------

T-F 18

H胡歌 28

Z周润发 50

M梅兰芳 100

------倒序排序-------

M梅兰芳 100

Z周润发 50

H胡歌 28

T-F 18

------根据姓名排序-------

H胡歌 28

M梅兰芳 100

T-F 18

Z周润发 50