List Sort kincolle’s blogs

If you want to sort a list especially when you want to sort by using elements of collections. At this time you can use sort function of Collections class.

First, let’s see a simple example:

public static void main(String[] args) {  
    List<Integer> nums = new ArrayList<Integer>();  
        nums.add(3);  
        nums.add(5);  
        nums.add(1);  
        nums.add(0);  
        System.out.println(nums);  
        Collections.sort(nums);  
        System.out.println(nums);  
}  

The result will be:

[3, 5, 1, 0]
[0, 1, 3, 5]

Then, let’s see a complex example:

public class User implements Comparable<User>{        
    private int score;        
    private int age;  

    public User(int score, int age){  
        super();  
        this.score = score;  
        this.age = age;  
    }  

    public int getScore() {  
        return score;  
    }  

    public void setScore(int score) {  
        this.score = score;  
    }  

    public int getAge() {  
        return age;  
    }  

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

    @Override  
    public int compareTo(User o) {  
        int i = this.getAge() - o.getAge();//order by age firstly  
        if(i == 0){  
            return this.score - o.getScore();//then order by socre  
        }  
        return i;  
    }  
}  

public static void main(String[] args) {  
        List<User> users = new ArrayList<User>();  
        users.add(new User(78, 26));  
        users.add(new User(67, 23));  
        users.add(new User(34, 56));  
        users.add(new User(55, 23));  
        Collections.sort(users);  
        for(User user : users){  
            System.out.println(user.getScore() + "," + user.getAge());  
        }  
}

Then the result will be

55,23
67,23
78,26
34,56