equal

[Jerry]

Does o1.equals(o2) imply o1==o2?

 

[Bob]

Does o1.equals(o2) imply o1==o2?

No, not necessarily.

a.equals(b) is a test for meaningful equivalence.

a == b is a test for the memory address of a against the memory address
of b. I.e. are a and b one object in memory?

 

[Ross Bamford]

Does o1.equals(o2) imply o1==o2?

Try it:

public static void main(String[] args) {
String s1 = new String("A string");
String s2 = new String("A string");
System.out.println("equals : "+s1.equals(s2)); // prints 'true'
System.out.println("identity: "+(s1 == s2)); // prints 'false'
}

So, no.

As an aside, if you use string literals for this then you will get see
true for both println statements, which demonstrates the string pooling
used by the JVM. You can see the same effect by 'internalising' the
strings as you create them.

String s1 = new String("A string").intern();
String s2 = new String("A string").intern();

s1 and s2 will reference the same object.

 

[Harald]

Does o1.equals(o2) imply o1==o2?

No, not at all: just because two things looks the same (equals()) they
need not be identical (==).

The other way round should better be true, however. Buggy
implementations of equals() may exist though.

Harald.