4,java list排序的2中方法

1. 利用Collections类的 java.util.Collections.sort(java.util.List, java.util.Comparator) 方法，自定义比较器对象对指定对象进行排序

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,代码如下：

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测试类

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);
        
        Listlist = 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());
        }
    }
}

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

2. 通过实现Comparable接口来实现list的排序
   假如现在我们有一个Person类的list集合，要让其按照一个Order属性进行排序，我们可以让Person类实现Comparable接口，重写其CompareTo方法即可,可以让程序按照我们想要的排列方式进行排序，如：这里我让Person按照order属性升序排序,具体实现如下：

Person实体类

public class Person implements Comparable{
    private String name;
    private Integer order;
 
    /**
     * @return the name
     */
    public String getName() {
        return name;
    }
 
    /**
     * @param name
     *            the name to set
     */
    public void setName(String name) {
        this.name = name;
    }
 
    /**
     * @return the order
     */
    public Integer getOrder() {
        return order;
    }
 
    /**
     * @param order
     *            the order to set
     */
    public void setOrder(Integer order) {
        this.order = order;
    }
 

    @Override
    public int compareTo(Person arg0) {
        return this.getOrder().compareTo(arg0.getOrder());      //这里定义你排序的规则。
    }
 }

测试类

public static void main(String[] args) {
    //初始化数据
    ListlistA = new ArrayList();
    Person p1 = new Person();
    Person p2 = new Person();
    Person p3 = new Person();
 
    p1.setName("name1");
    p1.setOrder(1);
    p2.setName("name2");
    p2.setOrder(2);
    p3.setName("name3");
    p3.setOrder(3);
 
    listA.add(p2);
    listA.add(p1);
    listA.add(p3);

    //排序
    Collections.sort(listA);

    //打印排序后的Person
    for (Person p : listA) {
        System.out.println(p.getName());
    }
}
结果：
name1
name2
name3