reverse analysis - One New Object per Character

With the input "Hello" six Strings are constructed (including the first, empty String) because each time the following statement executes, a new String is created:

rev += data.charAt(j);

As the statement starts to execute, rev refers to a String. The concatenation operator + creates a new String, a copy of the old one but with one more character on the end. The new String reference is assigned to rev. The old String is now garbage.
This is fine for programs that do a moderate amount of character manipulation. But such abundant construction of objects will slow down a program that does a great deal of character manipulation. Examples of such programs include word processors, compilers, assemblers, data base management systems, and many others.