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Strings and the Compiler

The compiler uses the StringBuilder class behind the scenes to handle literal strings and concatenation. As you know, you specify literal strings between double quotes:

"Hello World!"

You can use literal strings anywhere you would use a String object. For example, System.out.println accepts a string argument, so you could use a literal string there:

System.out.println("Might I add that you look lovely today.");

You can also use String methods directly from a literal string:

int len = "Goodbye Cruel World".length();

Because the compiler automatically creates a new string object for every literal string it encounters, you can use a literal string to initialize a string:

String s = "Hola Mundo";

The preceding construct is equivalent to, but more efficient than, this one, which ends up creating two identical strings:

String s = new String("Hola Mundo"); //don't do this

You can use + to concatenate strings:

String cat = "cat";
System.out.println("con" + cat + "enation");

Behind the scenes, the compiler uses string buffers to implement concatenation. The preceding example compiles to something equivalent to:

String cat = "cat";
System.out.println(new StringBuffer().append("con").
append(cat).append("enation").toString());

You can also use the + operator to append to a string values that are not themselves strings:

int one = 1;
System.out.println("You're number " + one);

The compiler implicitly converts the nonstring value (the integer 1 in the example) to a string object before performing the concatenation operation.

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