Page 2 - Java basic program guidance

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#16

November 15th, 2005, 01:56 PM

crownjewel82

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Be proud of yourself it looks good so far.

To answer your question:
You want your end loop condition to be what you're using to see if it's right. So the loop ends when the input is right.

Code:

boolean right = false;
while (right) {
  //enter word1:
  if (word1.length() <= 37) right = true;
}

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#17

November 15th, 2005, 01:56 PM

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Quote:

Originally Posted by mvantuyl

Actually, 'while' is a reserved word, but 'While' isn't. (But it still isn't a good idea to use 'While' as a class name)

True, I didn't catch that. Sorry for the mistake.

#18

November 15th, 2005, 01:59 PM

crownjewel82

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Something else I noticed:
You've got a stray while statement at the end there. Were you going for a do while loop? If so it's really not necessary.

#19

November 15th, 2005, 03:06 PM

Yawmark

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Quote:

You want your end loop condition to be what you're using to see if it's right. So the loop ends when the input is right.

It's never too soon to talk about design and/or refactoring. I generally like to break methods up into fairly atomic units of work. Again, once you have a decent algorithm, the code practically writes itself. Here's an example:

Pseudocode:
1) Ask the user for a word
2) Ask the user for another word
3) Display the words

That's the basic idea of the program. We'll see that each step has its own set of requirements, but let's just start with this algorithm of program flow.

Java Code:

Original - Java Code
public class Foo { private Foo() { } // prevent instantiation public static void main(String[] args) throws Exception { new Foo().go(); } void go() { String firstWord = getWordFromUser(); String secondWord = getWordFromUser(); displayWords(firstWord, secondWord); } }

public class Foo {    
    
    private Foo() { } // prevent instantiation
 
    public static void main(String[] args) throws Exception {
        new Foo().go();        
    }
    
    void go() {
        String firstWord  = getWordFromUser();
        String secondWord = getWordFromUser();
        displayWords(firstWord, secondWord);
    }
 
}

Okay, this obviously won't compile (the methods aren't defined), but I'm not too worried about it. This pretty much covers the main program, right? Now, we just need to define those methods. We'll write some basic methods as "stubs", just to get a working program...

Java Code:

Original - Java Code
private String getWordFromUser() { return "something"; } private void displayWords(String first, String second) { System.out.println("first: " + first + "\nsecond: " + second); }

 
    private String getWordFromUser() {
        return "something"; 
    }
    
    private void displayWords(String first, String second) {
        System.out.println("first: " + first + "\nsecond: " + second);
    }

Okay, this compiles and runs, so we can see that we've got a working skeleton. Let's tackle the next small piece: user input. Once again, let's write up our algorithm in pseudocode:

1) Get some input from the user
2) While the input is invalid
2a) Notify user of the error
2b) Try to get good input

Translated to Java, we get the following for our getWordFromUser() method:

Java Code:

Original - Java Code
private String getWordFromUser() { String input = getStringInput(); while(isTooLong(input)) { notifyUserStringTooLong(); input = getStringInput(); } return input; }

    private String getWordFromUser() {
        String input = getStringInput();
        while(isTooLong(input)) {
            notifyUserStringTooLong();
            input = getStringInput();
        }
        return input;
    }

Again, we've got more undefined methods, so let's stub it out...

Java Code:

Original - Java Code
private String getStringInput() { return "foo"; } private boolean isTooLong(String input) { return false; } private void notifyUserStringTooLong() { //... } private void quit() { System.exit(0); }

    private String getStringInput() {
        return "foo";
    }
    
    private boolean isTooLong(String input) {
        return false;
    }
    
    private void notifyUserStringTooLong() {
        //...
    }
            
    private void quit() {
        System.exit(0);
    }

So now, we've got a compiling and running program...

Java Code:

Original - Java Code

public class Foo {    
    
    private Foo() { } // prevent instantiation
 
    public static void main(String[] args) throws Exception {
        new Foo().go();        
    }
    
    void go() {
        String firstWord  = getWordFromUser();
        String secondWord = getWordFromUser();
        displayWords(firstWord, secondWord);
    }
    
    private String getWordFromUser() {
        String input = getStringInput();
        while(isTooLong(input)) {
            notifyUserStringTooLong();
            input = getStringInput();
        }
        return input;
    }       
    
    private String getStringInput() {
        return "foo";
    }
    
    private boolean isTooLong(String input) {
        return false;
    }
    
    private void notifyUserStringTooLong() {
        //...
    }
            
    private void quit() {
        System.exit(0);
    }
    
    private void displayWords(String first, String second) {
        System.out.println("first:  " + first + "\nsecond: " + second);
    }
 
}

So now, we can go in and handle each small stub...

Java Code:

Original - Java Code

    private String getStringInput() {
        String input = JOptionPane.showInputDialog("Please enter a word");
        if (input == null) quit();
        return input;
    }
    
    private boolean isTooLong(String input) {
        return input.length() > MAX_INPUT_LENGTH;
    }
    
    private void notifyUserStringTooLong() {
        JOptionPane.showMessageDialog(null,
            "Input can't be longer than " + MAX_INPUT_LENGTH + " characters");
    }
           
    private void quit() {
        System.exit(0);
    }

You'll notice the MAX_INPUT_LENGTH variable. It's a constant I chose to define because I loathe Magic Numbers. So once I define all that, I've got another compilable, runnable class I can test....

Java Code:

Original - Java Code

import javax.swing.JOptionPane;
 
public class Foo {  
    
    private final int MAX_INPUT_LENGTH = 37;
    
    private Foo() { } // prevent instantiation
 
    public static void main(String[] args) throws Exception {
        new Foo().go();        
    }
    
    void go() {