Java集合框架--List 排序

一、Java List 类
二、Java List 排序
三、Java List 遍历
四、Java List 去重
五、Java List 转Array

二、Java List排序（两种方法）

1. 利用Collections类的 java.util.Collections.sort(java.util.List, java.util.Comparator) 方法，自定义比较器对象对指定对象进行排序
对Person类对象按照起身高（降序）排序，当升高相同按id升序

// Person 类
class Person{
	private int id;
	private String name;
	private float tall;
	
	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;}
	
	public float getTall()  {return tall;}
	public void setTall(float tall)  {this.tall = tall;}
}
//比较器
class PersonComparator implements Comparator<Person>{
	public int compare(Person p1, Person p2 ) {
		if ( p1.getTall() > p2.getTall() ) return -1;
		else if ( p1.getTall() == p2.getTall() ) {
			if (p1.getId() > p2.getId() ) return 1;
			else if ( p1.getId() == p2.getId() ) return 0;
			else return -1;
		} 
		else return 1;
	}
}

public class listSort {
	public static void main(String[] args) {
		// TODO Auto-generated method 
		Person p1 = new Person();
		p1.setId(005);  p1.setName("Jerry");  p1.setTall(165);
		
		Person p2 = new Person();
		p2.setId(003);  p2.setName("Morty");  p2.setTall(171.1f);
		
		Person p3 = new Person();
		p3.setId(001); p3.setName("Rick"); p3.setTall(176);
		
		Person p4 = new Person();
		p4.setId(004);  p4.setName("Tom");  p4.setTall(171.1f);
		
		List<Person> list = new ArrayList<>();
		list.add(p1); list.add(p4); list.add(p3); list.add(p2);

		System.out.println("*****before sort*****");
		for(Person ps:list) 
			System.out.println("id: "+ps.getId()+ " name: "+ps.getName() + " score: " + ps.getTall() );
		Collections.sort(list, new PersonComparator());
		System.out.println("*****after sort*****");
		for(Person ps:list) 
			System.out.println("id: "+ps.getId()+ " name: "+ps.getName() + " score: " + ps.getTall() );
	}
}

运行结果

*****before sort*****
id: 5 name: Jerry score: 165.0
id: 4 name: Tom score: 171.1
id: 1 name: Rick score: 176.0
id: 3 name: Morty score: 171.1
*****after sort*****
id: 1 name: Rick score: 176.0
id: 3 name: Morty score: 171.1
id: 4 name: Tom score: 171.1
id: 5 name: Jerry score: 165.0

2. 利用Collections类的 java.util.Collections.sort(java.util.List, java.util.Comparator) 方法，自定义比较器对象对指定对象进行排序
对一个Person类，让其按照一个Order属性进行排序，我们可以让Person类实现Comparable接口，重写其CompareTo方法即可，如：让Person按照身高属性升序排序。

class Person implements Comparable<Person>{
	private String name;
	private Integer tall;									//compareTo只能是对象之间的比较，不能适用于int等基本类型，要使用int的封装类型Integer
	
	public String getName() {return name;}
	public void setName(String name) {this.name = name;}
	
	public Integer getTall() {return tall;}					
	public void setTall(Integer tall) {this.tall = tall;}
	
	public int compareTo(Person ps) {						//compareTo只能是对象之间的比较，不能适用于int boolean等基本类型
		return this.getTall().compareTo( ps.getTall() );    //这里定义排序规则
	}														
}
public class listSort2 {
	public static void main(String[] args) {
		// TODO Auto-generated method stub
	    List<Person> list = new ArrayList<>();
	    Person p1 = new Person();  Person p2 = new Person(); Person p3 = new Person();
	 
	    p1.setName("Rick");   	p1.setTall(174);
	    p2.setName("Morty");  	p2.setTall(178);
	    p3.setName("Jerry");	p3.setTall(176);
	    
	    list.add(p1);	list.add(p2);	list.add(p3);
	    //排序
	    Collections.sort(list);
	    for (Person p : list) {
	        System.out.println(p.getName());
	    }
	}
}

运行结果

Rick
Jerry
Morty