The offset/count fields are somewhat orthogonal to the pooling/intern() issues. Offset and count come when you have something like:

String substring = myString.substring(5);

One way to implement this method would be something like:

• allocate a new char[] with myString.length() - 5 elements
• copy all of the elements from index index 5 to myString.length() from myString to the new char[]
• substring is constructed with this new char[]
  • substring.charAt(i) goes directly to chars[i]
  • substring.length() goes directly to chars.length

As you san see, this approach is O(N) -- where N is the new string's length -- and requires two allocations: the new String, and the new char[]. So instead, substring works by resusing the original char[] but with an offset:

• substring.offset = myString.offset + newOffset
• substring.count = myString.count - newOffset
• use myString.chars as the chars array for substring
  • substring.charAt(i) goes to chars[i+substring.offset]
  • substring.length() goes to substring.count

Note that we didn't need to create a new char[], and more importantly, we didn't need to copy the chars from the old char[] to the new one (since there is no new one). So this operation is just O(1) and requires only one allocation, that of the new String.