集合框架--Map集合之HashMap存储自定义对象

将学生对象和学生的归属地通过键与值存储到map集合中。

import java.util.HashMap;
import java.util.Iterator;
import java.util.Set;


class Student {  
	String name;
	int age;

	public Student(String name,int age){
		super();
		this.name=name;
		this.age=age;
	}
	public String getName(){
		return name;
	}
	public void setName(String name){
		this.name=name;
	}
	public int getAge(){
		return age;
	}
	public void setAge(int age){
		this.age=age;
	}
 
}
public class HashMapDemo{
public static void main(String[] args){
	HashMap hm=new HashMap();

	hm.put(new Student("lisi",38),"北京");
	hm.put(new Student("zhaosi",34),"上海");
	hm.put(new Student("xiaoqiang",31),"沈阳");
	hm.put(new Student("wangcai",28),"大连");
	hm.put(new Student("zhaosi",34),"铁岭");

	Set keySet=hm.keySet();
	
	Iterator it=keySet.iterator();

	while(it.hasNext()){
			Student key=it.next();
			String value=hm.get(key);
			System.out.println(key.getName()+":"+key.getAge()+"..."+value);
		}
	}

}

当键一样时，其值并没有被覆盖，所以要判断键是否相同，HashMap需要定义hashCode和equals方法，在Student类中要复写方法：

import java.util.HashMap;
import java.util.Iterator;
import java.util.Set;


class Student {  
	String name;
	int age;

	public Student(String name,int age){
		super();
		this.name=name;
		this.age=age;
	}
	public String getName(){
		return name;
	}
	public void setName(String name){
		this.name=name;
	}
	public int getAge(){
		return age;
	}
	public void setAge(int age){
		this.age=age;
	}
	public int hashCode(){  //复写hashCode()
		return name.hashCode()+age;
	}

	public boolean equals(Object obj){  //复写equals

		if(this==obj) return true;

		if(!(obj instanceof Student))  throw new ClassCastException("类型错误");  //输入类型错误

		Student p = (Student)obj;//强制转换
		return this.name.equals(p.name) && this.age==p.age;  //说明姓名和年龄相同则为同一元素
	}
 
}
public class HashMapDemo{
public static void main(String[] args){
	HashMap hm=new HashMap();

	hm.put(new Student("lisi",38),"北京");
	hm.put(new Student("zhaosi",34),"上海");
	hm.put(new Student("xiaoqiang",31),"沈阳");
	hm.put(new Student("wangcai",28),"大连");
	hm.put(new Student("zhaosi",34),"铁岭");

	Set keySet=hm.keySet();	
	Iterator it=keySet.iterator();

	//以下被注释的代码可以替换上面两句:
	//Iterator it=hm.keySet().iterator();

	while(it.hasNext()){
			Student key=it.next();
			String value=hm.get(key);
			System.out.println(key.getName()+":"+key.getAge()+"..."+value);
		}
	}

}