Java List排序

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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.   */@Overridepublic int compare(Student s1, Student s2) {if(s1.getScore()>s2.getScore()){//greaterreturn -1;}else if(s1.getScore()==s2.getScore()){//equalsif(s1.getId()>s2.getId()){return 1;}else if(s1.getId()==s2.getId()){return 0;}else{return -1;}}else{//lessreturn 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