HashMap获取元素的两种方式 - 黑马程序员技术交流社区

/*
需求：将学生对象和地址存入到Map集合中，姓名和年龄相同视为同一个学生
*/
import java.util.*;
class HashMapTest
{
public static void main(String[] args)
{
HashMap<Student,String> hm=new HashMap<Student,String>();
hm.put(new Student("张三",18),"武汉");
hm.put(new Student("李四",19),"天津");
hm.put(new Student("王五",18),"西安");
hm.put(new Student("赵六",18),"北京");
hm.put(new Student("张三",18),"武汉");
/*
HashMap集合获取元素的第一种方式，迭代键的集合
Set<Student> set=hm.keySet();
Iterator<Student> it=set.iterator();
while(it.hasNext()){
Student stu=it.next();
String homeTown=hm.get(stu);
System.out.println("Student:"+stu+",homTown:"+homeTown);
}
*/
//HashMap集合获取元素的第二种方式，迭代映射关系
Set<Map.Entry<Student,String>> entry=hm.entrySet();
Iterator<Map.Entry<Student,String>> it=entry.iterator();
while(it.hasNext()){
Map.Entry<Student,String> me=it.next();
Student stu=me.getKey();
String homeTown=me.getValue();
System.out.println(stu+"来自"+homeTown);
}
}
}
class Student implements Comparable<Student>
{
private String name;
private int age;
Student(String name,int age){
this.name=name;
this.age=age;
}
public String getName(){
return name;
}
public int getAge(){
return age;
}
public int hashCode(){
return name.hashCode()+age*7;
}
//复写compareTo()方法，定义元素的比较方式
public int compareTo(Student stu){
int num=this.name.compareTo(stu.name);
if(num==0)
return new Integer(this.age).compareTo(stu.age);
return num;
}
//自定义equals方法，判断两个Person对象是否相同
public boolean equals(Object obj){
if(!(obj instanceof Student))
return false;
Student stu=(Student)obj;
return this.getName().equals(stu.getName())&&this.age==stu.age;
}
public String toString(){
return this.name+":"+this.age;
}
}

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