Java Programming - Java.lang Class - Discussion

Correct answer is B.

Because object class equals method compares address whereas in String class its overridden to compare the content.

So o.equals (s) will be false.

I have 2 comments:

1.A super class that is casted to a sub class is not fully "equals" because the static members remain of the super class. So if the static members of the subclass are needed, its not enough to check equals (or == operator).

2.The output is the same even when comparing with another string that only its value is the same (but in such a case operaton == returns false), since o object points now to the equals method of the instance of String that doesn't care about addresses difference :

String s1 = new String("foo");
String s2 = new String("foo");
Object o = (Object)s1;
if (s2.equals(o))
{
System.out.print("AAA");
}
else
{
System.out.print("BBB");
}
if (o.equals(s2))
{
System.out.print("CCC");
}
else
{
System.out.print("DDD");
}

Yes, I too got the same output, i.e AAACCC.

At o.equals(s) Object class equals method is executed & inside this equals method if both references i.e o[default "this" inside non static equals() method] & s refer to same object then 'true' is returned. thus;

sop("CCC") is executed.

At s.equals(o) , String class equals() method is executed, inside this equals method 1st code checks whether both references refer to same object see(https://dzone.com/articles/how-string-equals-method-works), hence true is returned & sop("AAA") is executed.

Its is obvious that both s and o's reference are same. In If conditions, it is given s.equals(o) which means to check whether both are referring to the same object. Since this condition is true it prints "AAA" and same way with the o.equals(s) so it prints "CCC".

Very interesting and motivation questions for Java programming.

String "s" is converted into an object O in which assign same value of String i.e. "fOO" that's why (s.equals(o) or o.equals(s)).

When you use == sign between two things, this is compare to the reference address equal or not. It means both variables having same data with same.

Reference address. If you use equals, it compare data values equal or not. In the above both are true. If == is true then equal is also equal data.

AS it is property of "equals" method that when two object to be compared using "equals" then.

1. If the two object are same type then, (in case of "string" class and "wrapper" class) it check the content. If content are same then it return "true" otherwise return "false".

2. If the two object are different then it try "cast" the two object in same type. If then can't be cast in same type then return "false" if the can be cast then check the content. If content is same then return "true" otherwise return "false".

Now,

if(s.equals (o))
Here jvm cast object "s" and "o" in same type and then check the content which is true.

Equals (-) method checking only the content of specified object is same as the passed parameter (or) not,

So that out put is AAACCC.