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：

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：

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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：