Java Cookbook

Reversing a String by Word or Character

Problem

You wish to reverse a string, a character or word at a time.

Solution

You can reverse a string by character easily, using a StringBuffer. There are several ways to reverse a string a word at a time. One natural way is to use a StringTokenizer and a stack. Stack is a class (defined in java.util; see Section 7.16) that implements an easy-to-use last-in, first-out (LIFO) stack of objects.

Discussion

To reverse the characters in a string, use the StringBuffer reverse( ) method.

// StringRevChar.java
String sh = "FCGDAEB";
System.out.println(sh + " -> " + new StringBuffer(sh).reverse(  ));

The letters in this example list the order of the sharps in the key signatures of Western music; in reverse, it lists the order of flats. Alternately, of course, you could reverse the characters yourself, using character-at-a-time mode (see Section 3.5).

A popular mnemonic or memory aid for the order of sharps and flats consists of one word for each sharp instead of just one letter, so we need to reverse this one word at a time. Example 3-4 adds each one to a Stack (see Section 7.16), then process the whole lot in LIFO order, which reverses the order.

Example 3-4. StringReverse.java

String s = "Father Charles Goes Down And Ends Battle"; // Put it in the stack frontwards Stack myStack = new Stack( ); StringTokenizer st = new StringTokenizer(s); while (st.hasMoreTokens()) myStack.push(st.nextElement( )); // Print the stack backwards System.out.print('"' + s ...