Java List排序

需求：對學生對象按照其 分數（降序）進行排序，當分數相同時按學號（從小到大）排序

實現：利用Collections類的 sort(List<T> list,Comparator<? super T> c) 方法，自定義比較器對象對指定對象進行排序

代碼實現

Student類

    class Student{  
        private int id;  
        private String name;  
        private float score;    //成績  

        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;  
        }  
    }  

    //先按成績 降序 排序，如果成績一樣的話按id 升序 排序  
    class StudentComparator implements Comparator<Student>{  

        /** 
          * 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;  
            }  
        }  
    }  

    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<Student> list = new ArrayList<Student>();  
            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());  
            }  
        }  
    }  

運行結果

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