Counting String objects created by Java code

Question

How many String objects are created by the following code?

String x = new String(\"xyz\");
String y = \"abc\";
x = x + y;

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Answer 1

The answer is 4.

As you have used the new keyword, Java will create a new String object in normal (non pool) memory and x will refer to it. In addition to this, the literal "xyz" will be placed in the string pool which is again another string object.

So, the 4 string objects are:

1. "xyz" (in non-pool memory)
2. "xyz" (in pool memory)
3. "abc" (in pool memory)
4. "xyzabc" (in non-pool memory)

If your code had been like this:

String x = "xyz";
String y = "abc";
x = x + y;

then the answer would be 3.

Note: String #4 is in non-pool memory because String literals and the strings produced by evaluating constant expressions (see JLS §15.28) are the only strings that are implicitly interned.

Source: SCJP Sun Certified Programmer for Java 6 (Page:434, Chapter 6)