String is interned.

[Ashu Jain]

As we know that string in hava is interned.
that is
String a1 = "hello friend";
String a3 = "hello" + "friend"

This will create 1 object and a3 will use existing string from pool.

I have two queries

(A) If we say System.out.println("My Problem is" + a3);
Does this creates another object "My Problem is" in string pool Or is this pooling applicable on only compile time constants.

(B) K&B says
String can2 = "7Up"
String word = "Up"
String can4 = "7" + word // This is not compile time constant

Since can4 is not compile time constant therefore it will use new string object rather than 7Up. Does that mean strings constants at compile time only use string pool.

Just confused

[Ashu Jain]

Any updates on this.

[Eric Daly]

From my understanding, a new object is created for every string literal, and added to the string pool. These are the compile-time constants. Every time you type a string in quotes, that is considered a string literal, and if it doesn't match a string already in the string pool when you compile, it is added. So, first of all, based on this understanding,

String a1 = "hello friend";
String a3 = "hello" + "friend"

creates FOUR objects (not just one as you had claimed). The three string literals, "hello friend", "hello", and "friend" are added to the pool during compilation. The fourth object, created and referenced by a3, is the string "hellofriend" which is not in the string pool, because it's created at runtime. Let's say you meant to say

String a3 = "hello " + "friend"

(which is what I'm guessing), then there would still be FOUR objects created, because the assignment

String a3 = "hello " + "friend"

is at runtime, so the compiler will not check the string pool for any matches.
Correct me if I'm wrong, but this is my understanding, from the K&B book.