Number of object created here

[Kaustubh G Sharma]

String s ="a";
s= s+"b"+"c";


question is been asked how many objects is been created here...

I said 4

They said no it's 5

Can anyone here explain me how ??

[Rob Spoor]

It's 5. Theoretically, that's because you don't have one String concatenation but two; s + "b" + "c" should be read as ((s + "b") + "c"). So the Strings:
- "a"
- "b"
- "c"
- "ab" (from s + "b")
- "abc" (from s + "b" + "c')

In practice it's also 5 but because of another reason. The compiler turns String concatenations into a StringBuilder. I've compiled and decompiled (with JAD) your example, and this is the result:

String s = "a";
s = (new StringBuilder()).append(s).append("b").append("c").toString();

That's still 5 objects:
- "a"
- "b"
- "c"
- the StringBuilder
- "abc", as a result of calling toString() on the StringBuilder

[Kaustubh G Sharma]

Thanks Rob but here we're not creating any object all we have is reference and string so where're the objects?

[Rob Spoor]

Every String literal is an object, so that's already three. I clearly see the word "new" there with the StringBuilder, so that's another one. And StringBuilder.toString() returns a new String object containing the same characters as the StringBuilder, so that's five.

[Stephan van Hulst]

And that's not even counting the objects StringBuilder is composed of!

[Kaustubh G Sharma]

got it Thanks guys