static String intern(String str) 
{
                                                         
    synchronized (internTable)
      {
        WeakReference ref = (WeakReference) internTable.get(str);
        if (ref != null)
          {
            String s = (String) ref.get();
            // If s is null, then no strong references exist to the String;
            // the weak hash map will soon delete the key.
            if (s != null)
              return s;
          }
        internTable.put(str, new WeakReference(str));
      }
    return str;
}

Fetches this String from the intern hashtable. If two Strings are considered equal, by the equals() method, then intern() will return the same String instance. ie. if (s1.equals(s2)) then (s1.intern() == s2.intern()). All string literals and string-valued constant expressions are already interned.