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

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

最后编辑于：2020.01.28 13:51:51