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
- 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