Java之List集合三种排序方式

方式一(Integer类型集合排序)

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);
}
/*
 * 输出结果
 * [3, 5, 1, 0]
 * [0, 1, 3, 5]
 */ 

方式二(对象类型集合排序)

package core.java.collection.collections;
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();//先按照年龄排序
		if(i == 0){
   
			return this.score - o.getScore();//如果年龄相等了再用分数进行排序
		}
		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());
	}
	/*
	 * 输出结果
	 * 55,23
	 * 67,23
	 * 78,26
	 * 34,56
	 */ 
}

我们会发现sort(List)方法中List中的T必须实现Comparable接口，然后实现compareTo（）方法，该方法的返回值0代表相等，1表示大于，-1表示小于；为什么在简单例子中没有看到实现Comparable接口呢？是因为Integer类其实自己已经实现了Comparable接口，Java已经给我们做好了。

方式三(同样是对象类型集合排序 )

package core.java.collection.collections;
public class Students {
   
	private int age;
	private int score;
	public Students(int age, int score){
   
		super();
		this.age = age;
		this.score = score;
	}
	public int getAge() {
   
		return age;
	}
	public void setAge(int age) {
   
		this.age = age;
	}
	public int getScore() {
   
		return score;
	}
	public void setScore(int score) {
   
		this.score = score;
	}
}
public static void main(String[] args) {
   
	List<Students> students = new ArrayList<Students>();
	students.add(new Students(23, 100));
	students.add(new Students(27, 98));
	students.add(new Students(29, 99));
	students.add(new Students(29, 98));
	students.add(new Students(22, 89));
	Collections.sort(students, new Comparator<Students>() {
   
		@Override
		public int compare(Students o1, Students o2) {
   
			int i = o1.getScore() - o2.getScore();
			if(i == 0){
   
				return o1.getAge() - o2.getAge();
			}
			return i;
		}
	});
	for(Students stu : students){
   
		System.out.println("score:" + stu.getScore() + ":age" + stu.getAge());
	}
	/*
	 * 输出结果
	 * score:89:age22
	 * score:98:age27
	 * score:98:age29
	 * score:99:age29
	 * score:100:age23
	 */
}

从上面的例子我们可以看出Students类没有实现Comparable接口，只是在sort()方法中多传入一个参数，只不过该参数是一个接口我们需要实现其compare方法。