Mixed Up Letters - String Functions

  Download Java Code

/*******************************************
Woody Wordword likes to play Scrabble.  He wants to practice
on his own, when no other players are available.  His idea is
to have the computer choose a random word, then scramble up
the letters and display the result.  Then he tries to guess
the original word, types his guess, and the computer tells
him whether he was correct. 
********************************************/

public class MixUp
{
  String[] words = {"hopeful", "unhappy", "worried", "liberty",
    "general", "trigger", "napkins", "showing",
    "legible", "rotated", "parsing", "fiddler"
  };
  public MixUp()
  {
    String chosen = chooseWord();
    output("The mixed up letters are: \n" + mixup(chosen));
    String answer = input("Your answer");
    if(answer.equalsIgnoreCase(chosen))
    {  output("Well done"); }
    else
    {  output("No, the word was " + chosen); } 
  }
  
  public String chooseWord()
  {
    int num = (int)(Math.random()*words.length);
    return words[num];
  }
  
  public String mixup(String w)
  {
    // take individual letters and store in an array
    // swapping is much easier in an array than a String
    String[] letters = new String[w.length()];
    for(int x = 0; x < w.length(); x=x+1)
    {
      letters[x] = w.substring(x,x+1);
    }
    
    // choose two random letters and swap, repeat 10 times
    for(int x = 0; x < 10; x=x+1)
    {
      int a = (int)(Math.random()*w.length());
      int b = (int)(Math.random()*w.length());
      String temp = letters[a];
      letters[a] = letters[b];
      letters[b] = temp;
    } 
    
    // concatenate letters from array back into a String
    String result = ""; 
    for(int x = 0; x < w.length(); x = x+1)
    {
      result = result + letters[x];      
    }
    
    return result;
  }
  
  public static void main(String[] args)
  {  new MixUp();  }
  
  public String input(String prompt)
  { return javax.swing.JOptionPane.showInputDialog(null,prompt); }
  
  public void output(String message)
  {  javax.swing.JOptionPane.showMessageDialog(null,message);  }
}

Random Numbers

The program scrambles the letters of a word as follows:

• choose two letters in two random positions
  
• exchange the positions of the two letters

The RANDOM positions are chosen by the Math.random( ) function.  It works like this:

• Math.random( )   ==>  choose a random decimal between 0 and 1 (never equals 0 or 1)
• multiply by w.length( )  ==> now it's between 0 and the length of the String, for example 7
                                                 but it's a decimal, like 5.123
• cast to an int value by using (int)

Scrambling Letters

The scrambling algorithm works like this:

• use a loop to copy all the letters into an Array of Strings, e.g.
  "HOPEFUL" ==>  letters[0] = "H"  ,  letters[1] = "O" , letters[2] = "P" ..... letters[6] = "L"
• choose two random positions, like 3 and 6
• swap the two letters in positions 3 and t (do this in the array)
  
• repeat swapping lots of times
• copy all the letters back from the Array into a single String

Programming Practice

• Download the program and run it.  Try solving a few puzzles.
• Add 4 more words.  But this time, they should NOT be 7 letters long. 
  Include some shorter words and some longer ones.
  Explain why the program still works correctly,
  without changing anything else to say how many words are in the list.
• Change the mixup( ) method so that it always leaves the first letter in the first position -
  this is a hint that makes the puzzles easier.
• Change the program so that it works a bit differently.
  -  There are two lists, one with colors and one with animals,
      like ["red","green","blue"] ... and ["dog","cat","rabbit"]
  - The program chooses a random color and a random animal.
  -  It joins the two words together, like "greenrabbit".
  - Now it mixes up this double-word.
  -  The user must guess the color and the animal, so they type in two separate answers.
  -  Both answers must be correct to win the game.