【补充版】HashMap（根据value筛选查找）

HashMap查找之根据Value查找

一般大家都知道对于HashMap而言都是通过key来进行查找。找到了key自然对应的value也就一并找到了。但是有些情况下就需要通过value来进行判断查找。说是查找不如说筛选更为恰当。

那么什么情况下会用到这种vaule查找方式呢？让我们一起来看一下以下代码就清楚了。

【1】面向对象学生类的创建

package com.java.demo_9;

/**
 * Student类
 * @author liupeng
 *
 */
public class Student {
    
    private String stuName;
    private String classCord;
    private String stuNumber;
    public String getStuName() {
        return stuName;
    }
    public void setStuName(String stuName) {
        this.stuName = stuName;
    }
    public String getClassCord() {
        return classCord;
    }
    public void setClassCord(String classCord) {
        this.classCord = classCord;
    }
    public String getStuNumber() {
        return stuNumber;
    }
    public void setStuNumber(String stuNumber) {
        this.stuNumber = stuNumber;
    }
    public Student() {
        super();
        // TODO Auto-generated constructor stub
    }
    public Student(String stuName,String stuNumber,String classCord) {
        super();
        this.stuName = stuName;
        this.classCord = classCord;
        this.stuNumber = stuNumber;
    }
    @Override
    public String toString() {
        return "学员名称:" + stuName + ", 学员编号:"
        + stuNumber + ", 班级番号:" + classCord;
    }
    
    

}

【2】面向对象筛选出相同classCord的同学

package com.java.demo_9;

import java.util.ArrayList;
import java.util.HashMap;

public class HashMapTest2 {
	public static void main(String[] args) {

		HashMap map = new HashMap();   //HashMap字典的创建并遍历出各个元素

		System.out.println("+++++++++++++++++++++++++++++++++++++++++++++++++++++++++");
		System.out.println("		<学员信息一览表>		");
		System.out.println();
		Student st1 = new Student("王小天", "cn0001", "class0001");
		Student st2 = new Student("张天爱", "cn0002", "class0002");
		Student st3 = new Student("武则天", "cn0003", "class0003");
		Student st4 = new Student("小钢炮", "cn0004", "class0004");
		Student st5 = new Student("屠龙刀", "cn0005", "class0002");
		Student st6 = new Student("小龙女", "cn0008", "class0002");
		Student st7 = new Student("三毛", "cn0006", "class0001");
		Student st8 = new Student("杨过", "cn0007", "class0002");
		
		map.put("王小天", st1);
		map.put("张天爱", st2);
		map.put("武则天", st3);
		map.put("小钢炮", st4);
		map.put("屠龙刀", st5);
		map.put("小龙女", st6);
		map.put("三毛", st7);
		map.put("杨过", st8);

		for (Object key : map.keySet()) {
			// System.out.println(key);
			Student value = (Student) map.get(key);
			System.out.println(key + ":" + value);
		}
		
		System.out.println("+++++++++++++++++++++++++++++++++++++++++++++++++++++++++");
		System.out.println();

		//创建3个ArrayList列表便于接受数据
		ArrayList list1 = new ArrayList();
		ArrayList list2 = new ArrayList();
		ArrayList list3 = new ArrayList();
		
　　　　　　　　  //通过for循环，if else循环语句来筛选隶属于相同班级的学生（list3例外）
		for(Object key:map.keySet()){
			Student obj = (Student)map.get(key);
			System.out.println(obj);
			if(obj.getClassCord().contains("class0002")){
				list1.add(obj);
			}else if(obj.getClassCord().indexOf("class0001")!=-1){
				list2.add(obj);
			}else{
				list3.add(obj);
			}
		}

　　　　　　　　　 //分别遍历出筛选过后的结果
		System.out.println("+++++++++++++++++++++++++++++++++++++++++++++++++++++++++");
		System.out.println("[class0002班级的学生有:]");
		System.out.println();
		
		for(Object obj:list1)
		System.out.println(obj);
		
		System.out.println("+++++++++++++++++++++++++++++++++++++++++++++++++++++++++");
		System.out.println("[class0001班级的学生有:]");
		System.out.println();
		
		for(Object obj:list2)
		System.out.println(obj);
		
		System.out.println("+++++++++++++++++++++++++++++++++++++++++++++++++++++++++");
		System.out.println("[其他班级的学生有:]");
		System.out.println();
		
		for(Object obj:list3)
		System.out.println(obj);
	
	}

}

结果：

【HashMap原字典信息】

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
		<学员信息一览表>		

三毛:学员名称:三毛, 学员编号:cn0006, 班级番号:class0001
屠龙刀:学员名称:屠龙刀, 学员编号:cn0005, 班级番号:class0002
张天爱:学员名称:张天爱, 学员编号:cn0002, 班级番号:class0002
小龙女:学员名称:小龙女, 学员编号:cn0008, 班级番号:class0002
杨过:学员名称:杨过, 学员编号:cn0007, 班级番号:class0002
小钢炮:学员名称:小钢炮, 学员编号:cn0004, 班级番号:class0004
王小天:学员名称:王小天, 学员编号:cn0001, 班级番号:class0001
武则天:学员名称:武则天, 学员编号:cn0003, 班级番号:class0003
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++

【属于class0002班级学员的信息】

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++

[class0002班级的学生有:]

学员名称:屠龙刀, 学员编号:cn0005, 班级番号:class0002
学员名称:张天爱, 学员编号:cn0002, 班级番号:class0002
学员名称:小龙女, 学员编号:cn0008, 班级番号:class0002
学员名称:杨过, 学员编号:cn0007, 班级番号:class0002
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++

 【属于class0001班级学员的信息】

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
[class0001班级的学生有:]

学员名称:三毛, 学员编号:cn0006, 班级番号:class0001
学员名称:王小天, 学员编号:cn0001, 班级番号:class0001
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++

  【其他班级学员的信息】

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
[其他班级的学生有:]

学员名称:小钢炮, 学员编号:cn0004, 班级番号:class0004
学员名称:武则天, 学员编号:cn0003, 班级番号:class0003
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++

 总结：

1. 创建3个ArrayList列表分别用来存放不同班级的信息.

2. 通过if ，else if ,else语句来判断属于不同班级的学生（根据classCord来判断）

3. 通过面向对象的方法调用Student类中.getClassCord()获取到classCord.

4. 通过.contains("元素")，.indexOf("元素")!=-1的任意一种方式结合if,else语句来进行筛选判断.

5. 分别遍历3个ArrayList中存入的元素.

方法很简单，相信java大神们肯定有更便捷的方法同样能够做到更好的效果。但是我是java初学者，这篇文章在此的目的只是希望能够帮助跟我一样初学java的同学们。

希望能有所帮助，谢谢。