Question about the java doc of String.intern() method

Question

hi all, my native language is not english, and i have a problem when reading the java doc of String.intern() method. the following text is extract from the documentation:
When the intern method is invoked, if the pool already contains a string equal to this String object as determined by the equals(Object) method, then the string from the pool is returned. Otherwise, this String object is added to the pool and a reference to this String object is returned.
i just don't know the "a reference to this String object is returned" part, does the "the reference to this String" means the string that the java keyword "this" represents or the string newly add to the string pool?
eg,
String s=new String("abc");  //create a string
s.intern();  //add s to the string pool, and return what? s itself or the string just added to string pool?greate thanks!

Answer 1

Except for primitives (byte, char, short, int, long, float, double, boolean), every value that you store in a variable, pass as a method parameter, return from a method, etc., is always a reference, never an object.
String s  = "abc"; // s hold a reference to a String object containing chars "abc"
foo(s); // we copy the reference in variable s and pass it to the foo() method.
String foo(String s) {
  return s + "zzz"; // create a new String and return a reference that points to it.
s.intern(); //add s to the string pool, and return what? s itself or the string just added to string pool?intern returns a reference to the String object that's held in the pool. It's not clear whether the String object is copied, or if it's just a reference to the original String object. It's also not relevant.