Java: Example - Replace word

Problem:

Write a method to replaces all occurences a word in a string with another word. Assume the method signature is

   static String replaceWord(String original, 
          String find, 
          String replacement)

Note that Strings are immutable, so we must create a new String. The word "replace" is probably misleading. Also, the method is static because it doesn't reference instance variables. This allows some optimizations by the compiler.

A simple, but incorrect, solution

This first attempt only replaces one word, but we could fix that up later with a loop -- but it's not worth the effort because it's wrong anyway.

//--------------------------------------------- replaceWord() 
// BAD BAD BAD BAD BAD  
static String replaceWord(String original, String find, String replacement) {
    int i = original.indexOf(find);
    if (i < 0) {
        return original;  // return original if 'find' is not in it.
    }
  
    String partBefore = original.substring(0, i);
    String partAfter  = original.substring(i + find.length());
  
    return partBefore + replacement + partAfter;
}

This example method replaces the first occurrence of a one string with another. If we execute the following code,

   t = "A great man";
   s = replaceWord(t, "man", "woman"); 

the value in s will be "A great woman". Ok, but what if we changed the orginal string to contain the word "human", or anything else that contained a substring, but not a separate word, that has "man" in it.

   t = "A great human";
   s = replaceWord(t, "man", "woman");

Now s will contain "A great huwoman". Not what was intended.

The solution is to know about "words"

Simply finding a substring isn't sufficient. There are several ways to solve the problem.

• Check the character preceding and following the string to see if they are delimiters, and can't be part of a w