java string concatenation and interning

Question

Question 1

String a1 = \"I Love\" + \" Java\";
String a2 = \"I Love \" + \"Java\";
System.out.println( a1 == a2 ); // true

String b1 = \"I Love\";
b1 += \"          


        

Answer 1

The first part of your question is simple: Java compiler treats concatenation of multiple string literals as a single string literal, i.e.

"I Love" + " Java"

and

"I Love Java"

are two identical string literals, which get properly interned.

The same interning behavior does not apply to += operation on strings, so b1 and b2 are actually constructed at run-time.

The second part is trickier. Recall that b1.intern() may return b1 or some other String object that is equal to it. When you keep a1 and a2, you get a1 back from the call to b1.intern(). When you comment out a1 and a2, there is no existing copy to be returned, so b1.intern() gives you back b1 itself.