Java List排序

jopen 7年前

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<T> list,Comparator<? super T> 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<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;                }            }        }  
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<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());                }            }        }  

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