JAVA-HashMap的应用例子

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import java.util.*;
class HashMapDemo2
{
public static void main(String[] args)
{
  HashMap<Student,String> hm = new HashMap<Student,String>();

  hm.put(new Student("张三", 20),"北京");
  hm.put(new Student("李四", 21),"西安");
  hm.put(new Student("王五", 15),"重庆");
  hm.put(new Student("赵六", 26),"成都");
  hm.put(new Student("小七", 12),"绵阳");
  hm.put(new Student("小七", 12),"绵阳"); //未覆盖hashCode方法和equals方法时，能够存入相同的元素.

  Set<Map.Entry<Student,String>> s = hm.entrySet();
  for(Iterator<Map.Entry<Student,String>> it = s.iterator();it.hasNext(); )
  {
   Map.Entry<Student,String> me = it.next();
   Student stu =me.getKey();
   String addr =me.getValue();
   System.out.println(stu.getName()+ ".." + stu.getAge() + ".." + addr);
  }
}
}

class 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() //注意，判断HashSet、HashMap集合的唯一性，覆盖hashCode和equals方法，而TreeMap、TreeMap排序实现comparable或comparator接口.
{
return name.hashCode() +age*29;
}

public boolean equals(Object obj)
{
  if (!(obj instanceofStudent))
   returnfalse;
  Student student =(Student)obj;
  returnthis.name.equals(student.name) &&this.age == student.age;
}

public String toString()
{
return name + ".." + age;
}
}