Java programming trace the output?

Question

What is the output of this code?
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 is 0 why? Please solve my doubt!!
because I lost this question in SoloLearn challenge.

Answer 1

'==' is a reference comparison.
c and d has same value but different reference. So
c.equals(d) will return true
c==d will return false

Answer 2

b