i'm bit curious about the concatenated string literals with +

[Ahmed Rezk]

specifically how many strings are created in the pool in the following

String text = "tex"+"t";

is it 1,2 or 3

[Rahul Bhattacharjee]

Originally posted by Ahmed Rezk:
specifically how many strings are created in the pool in the following

String text = "tex"+"t";

is it 1,2 or 3

3 , if the pool already doesnot have object with value tex , t , text.
and all these objects would be created in the private native pool of string.

[Jim Yingst]

While a strict reading of the JLS would imply that all three should be in the pool, in reality only one is. Which is fine because nothing in the program has any need at all for the substrings "tex" and "t" by themselves. The whole thing is resolved at compile time as a single string "text", and that's what gets stored. You can see this with a test program and the javap tool.

Given

public class Test {
    String foo = "bar" + "baz";
}

then typing

$ javac Test.java
$ javap -verbose Test

gives output

Compiled from "Test.java"
public class Test extends java.lang.Object
  SourceFile: "Test.java"
  minor version: 0
  major version: 50
  Constant pool:
const #1 = Method       #5.#14; //  java/lang/Object."<init>":()V
const #2 = String       #15;    //  barbaz
const #3 = Field        #4.#16; //  Test.foo:Ljava/lang/String;
const #4 = class        #17;    //  Test
const #5 = class        #18;    //  java/lang/Object
const #6 = Asciz        foo;
const #7 = Asciz        Ljava/lang/String;;
const #8 = Asciz        <init>;
const #9 = Asciz        ()V;
const #10 = Asciz       Code;
const #11 = Asciz       LineNumberTable;
const #12 = Asciz       SourceFile;
const #13 = Asciz       Test.java;
const #14 = NameAndType #8:#9;//  "<init>":()V
const #15 = Asciz       barbaz;
const #16 = NameAndType #6:#7;//  foo:Ljava/lang/String;
const #17 = Asciz       Test;
const #18 = Asciz       java/lang/Object;
 
{
java.lang.String foo;
 
public Test();
  Code:
   Stack=2, Locals=1, Args_size=1
   0:   aload_0
   1:   invokespecial   #1; //Method java/lang/Object."<init>":()V
   4:   aload_0
   5:   ldc     #2; //String barbaz
   7:   putfield        #3; //Field foo:Ljava/lang/String;
   10:  return
  LineNumberTable:
   line 1: 0
   line 2: 4
 

}

Note that both foo and barbaz appear in the constant table, but not bar or baz individually.

Incidentally, the reason I changed

String text = "tex" + "t";

into

String foo = "bar" + "baz";

is because I wanted the variable name to be different from the content, so that we could see that both were included. If you change this to be a local variable within a method, then the name foo will not be included in the constant table. I'll leave that as an excercise for anyone who wants to try it.

[Rahul Bhattacharjee]

What is JLS ?

[Rahul Bhattacharjee]

Sorry ; I got it ...java language seecification.

[Ahmed Rezk]

Really many thanks for such engineering why of proof