The return of String.intern() explained

Question

Consider:

String s1 = new StringBuilder(\"Cattie\").append(\" & Doggie\").toString();
System.out.println(s1.intern() == s1); // true why?
System.out.prin         


        

Answer 1

s2.intern() would return the instance referenced by s2 only if the String pool didn't contain a String whose value is "java" prior to that call. The JDK classes intern some Strings before your code is executed. "java" must be one of them. Therefore, s2.intern() returns the previously interned instance instead of s2.

On the other hand, the JDK classes did not intern any String whose value is equal to "Cattie & Doggie", so s1.intern() returns s1.

I am not aware of any list of pre-interned Strings. Such a list will most likely be considered an implementation detail, which may vary on different JDK implementations and JDK versions, and should not be relied on.