How to sort objects of a class in java

We need to sort the objects of the class according to a certain attribute (or multiple attributes) in the class. There are two ways to achieve this. One method is class implementation. Comparable<T> interface, and then call the Collections.sort(List) method to sort. The other method is that the class does not implement the Comparable<T> interface, When sorting, use the Collections.sort(List, Comparator<T>) method and implement the Comparator interface.

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First create a simple student class:

public class Student {
    
    private String name;
    
    private int age;
 
    public Student() {}
 
    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
 
    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;
    }
}

1. Implement Comparable

public class Student implements Comparable<Student>{
 
    private String name;
 
    private int age;
 
    public Student() {}
 
    public Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
 
    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;
    }
 
    /**
     * 将对象按姓名字典序升序排序
     * @param o
     * @return
     */
    @Override
    public int compareTo(Student o) {
        return this.name.compareTo(o.getName());
    }
 
    @Override
    public String toString() {
        return "Student{" +
                "name=&#39;" + name + &#39;\&#39;&#39; +
                ", age=" + age +
                &#39;}&#39;;
    }
}

2. Sort by implementing the Comparable<T> interface in the Collections.sort() method

public class Client {
 
    public static void main(String[] args){
        List<Student> students = new ArrayList<>();
        students.add(new Student("a", 18));
        students.add(new Student("c", 19));
        students.add(new Student("b", 20));
 
        Collections.sort(students, new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                return o1.getAge()>o2.getAge()? -1:(o1.getAge()==o2.getAge()? 0:1);
            }
        });
        for(Student student:students){
            System.out.println(student.toString());
        }
    }
 
}

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