Java的超类java.lang.Object定义了两个非常重要的方法：

public boolean equals(Object obj)
public int hashCode()

import java.util.HashMap;
 
public class Apple {
	private String color;
 
	public Apple(String color) {
		this.color = color;
	}
 
	public boolean equals(Object obj) {
		if (!(obj instanceof Apple))
			return false;	
		if (obj == this)
			return true;
		return this.color.equals(((Apple) obj).color);
	}
 
	public static void main(String[] args) {
		Apple a1 = new Apple("green");
		Apple a2 = new Apple("red");
 
		//hashMap stores apple type and its quantity
		HashMap<Apple, Integer> m = new HashMap<Apple, Integer>();
		m.put(a1, 10);
		m.put(a2, 20);
		System.out.println(m.get(new Apple("green")));
	}
}

public int hashCode(){
	return this.color.length();	
}

相关文章:

1. Java hashCode() and equals() Contract for the contains(Object o) Method of Set
2. HashMap vs. TreeMap vs. Hashtable vs. LinkedHashMap
3. Yet Another “Java Passes By Reference or By Value”?
4. What does a Java array look like in memory?

Java equals() and hashCode() Contract

Java中equals()和hashCode()的区别与联系,布布扣,bubuko.com

Java中equals()和hashCode()的区别与联系

原文：http://blog.csdn.net/sunling_sz/article/details/21707987