java自带的Collections.sort实现对象集合的排序(正序或者倒序)

1.实体类 

package com.test.model;

public class Student {
	private Integer id;    //学生id
	private String userName;    //学生姓名
	private Integer age;    //学生年龄
	
	

	public Student(Integer id, String userName, Integer age) {
		super();
		this.id = id;
		this.userName = userName;
		this.age = age;
	}

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public String getUserName() {
		return userName;
	}

	public void setUserName(String userName) {
		this.userName = userName;
	}

	public Integer getAge() {
		return age;
	}

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

	@Override
	public String toString() {
		return "Student [id=" + id + ", userName=" + userName + ", age=" + age ]";
	}

}

2.排序 

        Student stu1 = new Student(1, "小马", 10);
		Student stu2 = new Student(2, "小马2", 10);
		Student stu3 = new Student(3, "小马3", 30);
		Student stu4 = new Student(4, "小马4", 40);
		Student stu5 = new Student(5, "小马5", 50);

		List<Student> studentList = new ArrayList<Student>();
		studentList.add(stu1);
		studentList.add(stu2);
		studentList.add(stu3);
		studentList.add(stu4);
		studentList.add(stu5);

		System.out.println("排序前--:" + studentList.toString());
        
        //studentList:排序的对象
        //Student:学生对象
		Collections.sort(studentList, new Comparator<Student>() {
            
			@Override
			public int compare(Student o1, Student o2) {
                // 从大到小(按照学生id)
				//return o2.getId().compareTo(o1.getId());

                // 从小到大(按照学生id)
				//return o1.getId().compareTo(o2.getId());

				// 从大到小(按照年龄)
				return o2.getAge().compareTo(o1.getAge());

			}

		});

		System.out.println("倒序排序后--:" + studentList.toString());