Question

Possible Duplicate:
Questions about Java’s String pool

I have a doubt in java Strings object creation.

String s1 = "Hello"+"world";
String s2 = s1+"Java";

in this program how many String objects will be created and how ?please explain it.
Thanks.

Answer 1

The answer is 3

Two String objects will be created once per JVM start:

• “Helloworld”
• “Java”

Both will be interned, because they are constants (known at compile time).

They will be reused every time this code runs. A StringBuilder will be created to concatenate the two String above. References to them will be assigned to s1 and s2.

Here’s the bytecode for the code:

   0:   ldc #37; //String Helloworld
   2:   astore_1
   3:   new #39; //class java/lang/StringBuilder
   6:   dup
   7:   aload_1
   8:   invokestatic    #41; //Method java/lang/String.valueOf:(Ljava/lang/Object;)Ljava/lang/String;
   11:  invokespecial   #47; //Method java/lang/StringBuilder."<init>":(Ljava/lang/String;)V
   14:  ldc #50; //String Java
   16:  invokevirtual   #52; //Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
   19:  invokevirtual   #56; //Method java/lang/StringBuilder.toString:()Ljava/lang/String;
   22:  astore_2
   23:  return