public static String reverse( String data )
  {
    String rev = new String();

    for ( int j=data.length()-1; j >= 0; j-- )
      rev += data.charAt(j);

    return rev;
  }

How many objects does reverse() construct in this example?

A good answer might be:

The length of the input String, plus one.

One New Object per Character

When the input is "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 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. Such programs are word processors, compilers, assemblers, data base programs, and many others.

QUESTION 4:

Could an array of char be used to speed up this program?