okay what am i doing wrong?

[f. nikita thomas]

i'm trying to check the Reference class for equality...

public class Reference {
	int i;
	String name = null;
	Reference r = null;
	public Reference(int i,String name,Reference r){
		this.i = i;
		this.name = name;
		this.r = r;
	}
	public boolean equals(Object obj){
		if(obj == this)
			return true;
		if(obj == null)
			return false;
		if(!(getClass() == obj.getClass()))
			return false;
		else
		return (this.i == ((Reference)obj).i)
				&&(this.name.equals(((Reference)obj).name));
		
	}

}   

but when i check...

 
public class RefCheck {

	public static void main(String[] args) {
		Reference t = new Reference(5,"james",null);
		Reference r0 = new Reference(5,"james",null);
		Reference s = new Reference(5,"james",t);
		String x = "willy";
		String y = "willy";
		String i = "wally";
		String j = "wi";
		j+="lly";
		System.out.println(x==y);
		System.out.println(x==i);
		System.out.println(x==j);
		System.out.println(r0.equals(s));
		System.out.println(r0.equals(t));
		System.out.println(r0.equals(r0));

	}

}

i get this...

true
false
false
true
true
true

shouldn't r0.equals(s) return false? what is the correct way to check for reference equality in a class? any help will be greatly appreciated. thanks in advance.

[Rob Spoor]

Why should r0 and s be unequal? They both have 5 and "james" as their values. Your equals method only uses "i" and "name", it ignores "r".

Also, don't forget to override hashCode(), or you will run into unexpected behaviour when using HashSet or HashMap.

[f. nikita thomas]

   
public boolean equals(Object obj){
		if(obj == this)
			return true;
		if(obj == null)
			return false;
		if(!(getClass() == obj.getClass()))
			return false;
		else
		return (this.i == ((Reference)obj).i)
				&&(this.name.equals(((Reference)obj).name))
                                &&this.r==((Reference)obj).r;
		
	}

silly me, that wasn't the talking end...

[f. nikita thomas]

thanks Rob. how do i override hashCode() correctly?

[Campbell Ritchie]

There is an article about that in Joshua Bloch's book. Fortunately it (older edition) is available free of charge here. Note that in newer editions the instruction to multiply by 37 has changed to multiply by 31. You can also find details by googling "angelika langer hashcode java" but that only helps if you can read German.

[f. nikita thomas]

and thank you Campbell. i've been looking for something akin to this article for awhile. googling gives such " ",<insert expletive>,results that knowing what is true or correct leaves you at best concerned and at worst implementing bad practices. i'm reading the article now and it's by far the most comprehensible i've seen. again, thank you. take care.

[Harshit Rastogi]

you can go through this link also :Use of hashcode and equals

[Campbell Ritchie]

You're welcome And that article Harshit Rastogi posted looks good, too.