Java List排序

需求：对学生对象按照其 分数（降序）进行排序，当分数相同时按学号（从小到大）排序

实现：利用Collections类的 sort(List list,Comparator c) 方法，自定义比较器对象对指定对象进行排序

代码实现

Student类

class Student{
	private int id;
	private String name;
	private float score;	//成绩
	
	public int getId() {
		return id;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public float getScore() {
		return score;
	}
	public void setScore(float score) {
		this.score = score;
	}
}

比较器类

//先按成绩 降序 排序，如果成绩一样的话按id 升序 排序
class StudentComparator implements Comparator{

	/**
	  * return a negative integer, zero, or a positive integer as the first argument is less than, 
	  * 			equal to, or greater than the second. 
	  */
	@Override
	public int compare(Student s1, Student s2) {
		
		if(s1.getScore()>s2.getScore()){	//greater
			return -1;
		}else if(s1.getScore()==s2.getScore()){	//equals
			if(s1.getId()>s2.getId()){
				return 1;
			}else if(s1.getId()==s2.getId()){
				return 0;
			}else{
				return -1;
			}
		}else{	//less
			return 1;
		}
	}
}

Demo类

public class ListSortDemo {

	public static void main(String[] args) {
		
		Student s1 = new Student();
		s1.setId(10001);
		s1.setName("cat");
		s1.setScore(99.5f);
		
		Student s2 = new Student();
		s2.setId(10008);
		s2.setName("bba");
		s2.setScore(100.0f);
		
		Student s3 = new Student();
		s3.setId(10011);
		s3.setName("bac");
		s3.setScore(89.5f);
		
		List list = new ArrayList();
		list.add(s1);
		list.add(s2);
		list.add(s3);
		
		System.out.println("排序之前-----------------------");
		for(Student stu:list){
			System.out.println("id="+stu.getId()+" name="+stu.getName()+" score="+stu.getScore());
		}
		
		Collections.sort(list, new StudentComparator());	//排序
		
		System.out.println("排序之后-----------------------");
		for(Student stu:list){
			System.out.println("id="+stu.getId()+" name="+stu.getName()+" score="+stu.getScore());
		}
	}
}

运行结果

排序之前-----------------------
id=10001 name=cat score=99.5
id=10008 name=bba score=100.0
id=10011 name=bac score=89.5
排序之后-----------------------
id=10008 name=bba score=100.0
id=10001 name=cat score=99.5
id=10011 name=bac score=89.5