java集合中对象某属性比较排序Comparable与Comparator

要对集合中的对象的某属性进行排序有两种方式。

a. 一种是要排序对象类实现comparable接口的compareTo方法；然后把对象放入list；然后调用Collections.sort(list);
b. 一种是不对要排序对象类做任何改动，创建Comparator接口的实现类C；然后 把对象放入list；然后调用Collections.sort(list, C);

a.eg

----------------------------------

public class User implements Comparable<User>{
    private String name;
    private int age;
    private int gender;
    private String address;
    
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    
    public int getAge() {
        return age;
    }
    
    public void setAge(int age) {
        this.age = age;
    }
    
    public int getGender() {
        return gender;
    }
    
    public void setGender(int gender) {
        this.gender = gender;
    }
    
    public String getAddress() {
        return address;
    }
    
    public void setAddress(String address) {
        this.address = address;
    }
    
    public User() {
        super();
    }
    
    public User(String name, int age, int gender, String address) {
        super();
        this.name = name;
        this.age = age;
        this.gender = gender;
        this.address = address;
    }
   

    @Override
    public int compareTo(User o) {
        if(o!=null){
            if(this.getAge()>o.getAge()){

               return 1;
            }else if(this.getAge()==o.getAge()){

               return 0;

            }

       }
        return -1;
    }
}

-------------------------------------------main

List<User> ulist = new ArrayList<User>();
ulist.add(new User("wangbo",29,1,"长沙"));
ulist.add(new User("wumei",44,1,"株洲"));
ulist.add(new User("zhangjie",19,1,"岳阳"));
ulist.add(new User("lihua",36,1,"长沙"));
ulist.add(new User("zhangchangzhe",19,1,"衡阳"));

Collections.sort(list);

for(User u:ulist){
            System.out.println(u.getName()+"	"+u.getAge()+"	"+u.getAddress());
}

 

==============================================

b.eg

--------------------------------

public class User {
    private String name;
    private int age;
    private int gender;
    private String address;
    
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    
    public int getAge() {
        return age;
    }
    
    public void setAge(int age) {
        this.age = age;
    }
    
    public int getGender() {
        return gender;
    }
    
    public void setGender(int gender) {
        this.gender = gender;
    }
    
    public String getAddress() {
        return address;
    }
    
    public void setAddress(String address) {
        this.address = address;
    }
    
    public User() {
        super();
    }
    
    public User(String name, int age, int gender, String address) {
        super();
        this.name = name;
        this.age = age;
        this.gender = gender;
        this.address = address;
    }
    
}

 

------------------------------

import java.util.Comparator;

public class ComparatorImpl implements Comparator<User>{

    @Override
    public int compare(User o1, User o2) {
        
        if(null!=o1 && null!=o2){
            if(o1.getAge() >o2.getAge()){
                return 1;
            }else if(o1.getAge() ==o2.getAge()){
                return 0;
            }
        }
        return -1;
    }

}

-----------------------------------main

List<User> ulist = new ArrayList<User>();
        ulist.add(new User("wangbo",29,1,"长沙"));
        ulist.add(new User("wumei",44,1,"株洲"));
        ulist.add(new User("zhangjie",19,1,"岳阳"));
        ulist.add(new User("lihua",36,1,"长沙"));
        ulist.add(new User("zhangchangzhe",19,1,"衡阳"));
        Collections.sort(ulist, new ComparatorImpl());
        for(User u:ulist){
            System.out.println(u.getName()+"	"+u.getAge()+"	"+u.getAddress());
        }