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

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