Need an explanation

Question

public class Program
{
public static void main(String[] args) {
String a = "a";
String b = "b";
String c = a + b;
String d = "ab";
if (c==d) {
System.out.println(1);
} else {
System.out.println(0);
}
}
}
Output: 0
Why?

Answer 1

Operator == in Java compares objects, but you need to compare just values of this objects. So to get correct result use .equals() method of String.

Answer 2

== is used in java for reference comparsion. c and d in your code are different references.

Answer 3

you need to compare strings using .equals()