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

Hopefully you're getting the idea here. Solve your problems by tackling one small thing at a time. Think of the algorithm first, then write code in a stepwise fashion. Test each little bit as you go. Hopefully this simple example will start you well on your way toward completing your program.

Good luck!

Comments on this post

Guelphdad agrees: In depth answers like this are why I love Dev Shed! Wonderful.

LynxLee agrees: Wow, I agree with Guelphdad.. and you too. :P

canadiancreed agrees: Very nice

tcjohans agrees: great

#20

November 15th, 2005, 03:20 PM

mvantuyl

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WOW!

That post should be stickied and made required reading for anybody learning programming.

#21

November 15th, 2005, 03:32 PM

crownjewel82

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If I ever get off my lazy behind and do it. I plan on having a programming tutorial site with my methodology. Might even publish it into a book. "How to Program the Right Way"

#22

November 16th, 2005, 04:41 AM

Calaen

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Ok I have tidied it up abit I think

But I still cant seem to get it to loop back to the inputs if there is an error in the length of the word. I really appreciate the help so far aswell, it has giving me a much better understanding of programming.

Code:

import javax.swing.*;
 
 class Homework9 
 {
   public static void main (String args[]) 
	{
	  int length1, length2;
	  //input a word  
	  String input1 = JOptionPane.showInputDialog("Enter first word");
      length1 = input1.length();
	  if (input1.length() > 37)
	  
	  //prints an error message if the length of word 1 exceeds 37 characters	    		    
	  JOptionPane.showMessageDialog(null,"Error",
      "Error word length exceeds 37", JOptionPane.ERROR_MESSAGE);
      
      //input a second word      
      String input2 = JOptionPane.showInputDialog("Enter second word");
	  length2 = input2.length();
	  if (input2.length() > (38-length1))	    		    
		    
	  //prints an error message if the length of word 1 and word 2 exceeds 38 characters    
	  JOptionPane.showMessageDialog(null,"Error total length of words exceeds 38 characters",
      "Error", JOptionPane.ERROR_MESSAGE);
            
      //how long is input1
	  int i = input1.length();
	  //print input 1
	  System.out.print(input1);
      //keep printing dots till there is only room left for input 2
	  while (i < (40 - input2.length())) 
	  {
	    System.out.print(".");
		i++;
             
      }
		//print input 2
	    System.out.println(input2);
		 
		
		
	}
}

Cheers.

#23

November 16th, 2005, 07:21 AM

Yawmark

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Quote:

Ok I have tidied it up abit I think

Everything is still piled into the main method, and begs to be refactored. Each method should do one thing, and do it well. Don't make your main method work so hard...

Quote:

But I still cant seem to get it to loop back to the inputs if there is an error in the length of the word.

Either you haven't yet developed an understanding of what the algorithm for such an action should be, or you don't understand how to translate that algorithm to Java. Either way, you haven't written your program to "loop back to the inputs"; you must tell the computer what you want it to do, and there's nothing in your example that says "keep trying to get input if it isn't correct". Please study the code I posted, especially the getWordFromUser() method.

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class Sig{public static void main(String...args){\u0066or(int
\u0020$:"vÌÈÊ\"¤¾ÀÊ²¬Æ\"v¤Î¤\"²¤¨¸¬Æ".to\u0043h\u0061rArray()
)System./*goto/*$/%\u0126//^\u002A\u002Fout.print((char)(($>>
+(~'"'&'#'))+('<'>>('\\'/'.')/\u002Array.const(~1)\*\u002F)));}}

Last edited by Yawmark : November 16th, 2005 at 07:24 AM.

#24

November 16th, 2005, 08:47 AM

Calaen

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Sorted it, I was using if's instead of whiles and I have broken it down some. Thanks alot for the input guys, I like how you didnt just drop an answer to my question without trying to make me understand what it was I was trying to achieve. I will no doubt have many more questions as I try and gain a wider understanding of Java.

Thanks again.

Stephen

Comments on this post

crownjewel82 agrees: Thanks for not being lazy and wanting help not handouts.

Yawmark agrees: Glad you're working on it. Your success is due, no doubt, to your regal first name...

gimp agrees!

#25

December 14th, 2005, 05:01 PM

bobber205

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This topic is great!

I acutally read the whole thing.

I'm really getting into Java not with as much difficulty just because I have programmed before. I'm not so sure Java is the best language to start with.

Years ago I used "Learn To Program Basic". Fun stuff.

Then I went straight into REALbasic, now Java.

Good luck.

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