HashMap的使用

package test;

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

public class MapDemo2 {

	public static void main(String[] args) {
		// TODO 自動生成的方法存根
		HashMap<Student,String> hashMap = new HashMap<Student,String>();
		hashMap.put(new Student("zhangsan",21), "male");
		hashMap.put(new Student("lisi",22), "female");
		hashMap.put(new Student("wangwu",21), "male");
		hashMap.put(new Student("wangwu",21), "female");
		//使用entrySet方法同樣可以對Map中元素進行迭代取出
		Set<Map.Entry<Student,String>> set = hashMap.entrySet();
		Iterator<Map.Entry<Student, String>> it = set.iterator();
		while(it.hasNext()){
			Map.Entry<Student, String> student = it.next();
			Student key = student.getKey();
			String value = student.getValue();
			System.out.println(key + ":" + value);
		}
	}

}

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;
	}
	@Override
	public String toString() {
		return "Student [name=" + name + ", age=" + age + "]";
	}
	public int hashCode(){
		return name.hashCode() + age*3;
	}
	public boolean equals(Object obj){
		if(!(obj instanceof Student)){
			throw new ClassCastException();
		}
		Student stu = (Student) obj;
		return this.name.equals(stu.name) && this.age == stu.age;
	}
	@Override
	public int compareTo(Student o) {
		int flag = new Integer(this.age).compareTo(new Integer(o.age));
		if(flag == 0){
			return this.name.compareTo(o.name);
		}else{
			return flag;
		}
	}
}

輸出結果爲：

由於重寫了hashCode和equals方法，HashMap保證了鍵的唯一性，所以當試圖hashMap.put(new Student("wangwu",21), "female")，會替換該鍵的舊值，

最後輸出Student [name=wangwu, age=21]:female