Are Strings also static: String creation within Methods

Question

I know that at compile time when a String is created, that String will be THE string used by any objects of that particular signature.

String s = "foo"; <--Any other identical strings will simply be references to this object.

Does this hold for strings created during methods at runtime? I have some code where an object holds a piece of string data. The original code is something like

for(datum :data){
    String a = datum.getD();  //getD is not doing anything but returning a field

    StringBuffer toAppend = new StringBuffer(a).append(stuff).toString();

    someData = someObject.getMethod(a);
    //do stuff

}

Since the String was already created in data, it seems better to just call datum.getD() instead of creating a string on every iteration of the loop.

Unless there's something I'm missing?

Answer 1

String instances are shared when they are the result of a compile-time constant expression. As a result, in the example below a and c will point to the same instance, but b will be a different instance, even though they all represent the same value:

String a = "hello";
String b = hell() + o();
String c = "hell" + "o";

public String hell() {
   return "hell";
}

public String o() {
   return "o";
}

You can explicitly intern the String however:

String b = (hell() + o()).intern();

In which case they'll all point to the same object.

Answer 2

The line

 String a = datum.getD();

means, assign the result of evaluating datum.getD() to the reference a . It doesn't create a new String.