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标题: 对象排序 [打印本页]

作者: 张海刚 时间: 2011-7-28 19:13
标题: 对象排序
如何使用对象的属性对对象进行排序？

作者: 杨志罡 时间: 2011-7-28 20:42
Demo：按学生成绩进行排序
定义一个student类[code=java]package com.cast.heima;

public class Student {

private int score;

private int id;

public int getScore() {
return score;
}

public void setScore(int score) {
this.score = score;
}

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public Student(int score, int id) {
super();
this.score = score;
this.id = id;
}

@Override
public String toString() {
return "Person [score=" + score + ", id=" + id + "]";
}
}[/code]排序运行类[code=java]package com.cast.heima;

import java.util.Comparator;
import java.util.Iterator;
import java.util.TreeSet;

public class MySort {

public static void main(String[] args) {
@SuppressWarnings({ "rawtypes", "unused", "unchecked" })
               //实例化一个TreeSet，初始化是传递一个Comparator比较器
TreeSet<Student> set = new TreeSet<Student>(new Comparator(){

@Override
public int compare(Object o1, Object o2) {
Student p1 = (Student)o1;
Student p2 = (Student)o2;
return p1.getScore()-p2.getScore();
}

});
               //实例化5个Student并对成员变量赋初始值
Student student1 = new Student(100, 1);
Student student2 = new Student(38, 2);
Student student3 = new Student(60, 3);
Student student4 = new Student(70, 4);
Student student5 = new Student(45, 5);
               //把五个对象放入带比较器的set中
set.add(student1);
set.add(student2);
set.add(student3);
set.add(student4);
set.add(student5);
//使用迭代器对set集合进行迭代并打印
for(Iterator<Student> iter = set.iterator();iter.hasNext();){
System.out.println(iter.next());
}
}
}
运行结果：
Student [score=38, id=2]
Student [score=45, id=5]
Student [score=60, id=3]
Student [score=70, id=4]
Student [score=100, id=1][/code]
[ 本帖最后由杨志罡于 2011-07-28  20:47 编辑 ]

作者: 匿名 时间: 2011-7-28 21:30
谢谢你的思路还是很清晰的看得比较明白。

作者: 匿名 时间: 2011-7-28 22:50
[code]import java.util.*;
class TreeSetDemo
{
  public static void main(String[] args)
  {
   TreeSet ts=new TreeSet();

   ts.add(new Student("zhangsan",11));
   ts.add(new Student("lisi",12));
   ts.add(new Student("wangwu",13));
   ts.add(new Student("zhaoliu",14));

   Iterator it=ts.iterator();
   while(it.hasNext())
   {
      //System.out.println(it.next());
      Student stu=(Student)it.next();
      System.out.println(stu.getName()+"::"+stu.getAge());
   }

  }
}

class Student implements Comparable       //Comparable接口强制让学生具备比较性。
{
private String name;
private int age;

public Student(String name,int age)
{
   this.name=name;
   this.age=age;
}

public int compareTo(Object obj)
{
      if(!(obj instanceof Student))
         throw new RuntimeException("不是学生对象");
      Student s=(Student)obj;


      if(this.age>s.age)
         return 1;
      if(this.age==s.age)
      {
         return this.name.compareTo(s.name);//判断次要条件。
      }
      return -1;


}
public String getName()
{
   return name;
}

public int getAge()
{
   return age;
}
}[/code]也可以让一个类继承Comparable接口。运行结果如下:
zhangsan::11
lisi::12
wangwu::13
zhaoliu::14

作者: 匿名 时间: 2011-7-28 23:01
分别取出两个对象的某个属性（如成绩）并对比该两属性大小，得出大小后将[color=Red]整个对象进行交换[/color] 而不是单单交换比较的那两个属性[code=java]package com.student;

import java.util.ArrayList;
import java.util.List;

public class Student {
private String name;
public  int Score;

public Student(){}

public Student(String name, int corse) {
super();
this.name = name;
this.Score = corse;
}

public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getCorse() {
return Score;
}
public void setCorse(int corse) {
this.Score = corse;
}

public static void sortByScore(List<Student> list){//因为排序不属于莫个成员变量特有的属性所这里用了static 修饰符
Student s=null;
for (int i = 0; i < list.size()-1; i++) {
for (int j = list.size()-1; j >i; j--) {
if(list.get(j).Score>list.get(j-1).Score){
//交换的是整个Student对象
s=list.get(j);
list.set(j, list.get(j-1));
list.set(j-1, s);
}
}
}
}

public static void printout( ArrayList<Student>list){
for (int i = 0; i < list.size(); i++) {
System.out.println(list.get(i).name+"  "+list.get(i).Score);
}
}

public static void main(String []args){
ArrayList<Student> list =new  ArrayList <Student>() ;
Student stu=new Student("张三", 85);
list.add(stu);

Student stu1=new Student();
stu1.setName("李四");
stu1.setCorse(88);
list.add(stu1);

Student stu2=new Student();
stu2.setName("王五");
stu2.setCorse(68);
list.add(stu2);

Student stu3=new Student();
stu3.setName("赵六");
stu3.setCorse(98);
list.add(stu3);

Student stu4=new Student();
stu4.setName("兰兰");
stu4.setCorse(96);
list.add(stu4);

Student.sortByScore(list);
Student.printout(list);

int []a={4,7};
a.toString();
}
}[/code]结果[code=java]赵六  98
兰兰  96
李四  88
张三  85
王五  68[/code]一定要把整个Student对象交换

作者: 匿名 时间: 2011-7-29 00:44
标题: 回复楼主的帖子
例如：[code]//对学生进行成绩排序
//应用Comparable 接口实现排序
import java.util.*;
class Student implements Comparable<Student>
{
private String name;
private int age;
private double result;
public Student(String n,int a,double r)
{
name = n;
age = a;
result = r;
}
public String getName()
{
return name;
}
public int getAge()
{
return age;
}
public double getResult()
{
return result;
}
public int compareTo(Student other)
{
if(result < other.result) return -1;
if(result > other.result) return 1;
return 0;
}
}
public class StudentSortTest
{
public static void main(String[] args)
{
Student[] staff = new Student[5];

staff[0] = new Student("wang",13,50.5);
staff[1] = new Student("wang",13,80.0);
staff[2] = new Student("wang",13,90.5);
staff[3] = new Student("wang",13,70.0);
staff[4] = new Student("wang",13,60.5);

Arrays.sort(staff);
for(Student e : staff)
System.out.println("name=" + e.getName() + ",age=" + e.getName() + ",result=" + e.getResult());
}
}[/code]

作者: 匿名 时间: 2011-7-29 00:53
标题: 回复
我个人一般是先创建包含对象属性的数组，然后用快速排序即Arrays.sort(数组名);
希望对您有帮助。

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