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<Student,String> hm=new HashMap<Student,String>();
 
    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<Student> keySet=hm.keySet();
  
    Iterator<Student> it=keySet.iterator();
 
  while(it.hasNext()){
          Student key=it.next();
          String value=hm.get(key);
           System.out.println(key.getName()+“:”+key.getAge()+“…”+value);
       }
   }
 
}

运行结果：

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<Student,String> hm=new HashMap<Student,String>();
 
    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<Student> keySet=hm.keySet();  
    Iterator<Student> it=keySet.iterator();
 
  //以下被注释的代码可以替换上面两句:
   //Iterator<Student> it=hm.keySet().iterator();
 
 while(it.hasNext()){
          Student key=it.next();
          String value=hm.get(key);
           System.out.println(key.getName()+":"+key.getAge()+"..."+value);
       }
   }
 
}

运行结果：