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Thread: java me how to: input - math operation - output

  1. #1
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    Exclamation java me how to: input - math operation - output

    OK, I have this trouble. I want to create an app, which performs this simple task.

    - Accepts numbers as an input from the phone keyboard
    - Makes some operations
    - Shows the results as an output

    So, my question is this: How do I create input, math operations and result output for a MIDlet??

    ( for example adding 2 integers etc. )

    Details:

    I did this quite easily in Java and ran the program via PC and command prompt ( using a class, main method and no GUI! ).

    1 
    2 
    3	import java.util.Scanner; // program uses class Scanner
    4
    5	public class Addition
    6 {
    7 // main method begins execution of Java application
    8	 public static void main( String args[] )
    9 {
    10	 // create Scanner to obtain input from command window
    11	 Scanner input = new Scanner( System.in );
    12
    13	 int number1; // first number to add
    14	 int number2; // second number to add
    15	 int sum; // sum of number1 and number2
    16
    17 System.out.print( "Enter first integer: " ); // prompt
    18	 number1 = input.nextInt(); // read first number from user
    19
    20 System.out.print( "Enter second integer: " ); // prompt
    21	 number2 = input.nextInt(); // read second number from user
    22
    23	 sum = number1 + number2; // add numbers
    24 
    25	 System.out.printf( "Sum is %d\n", sum ); // display sum
    26
    27 } // end method main
    28
    29} // end class Addition

    But what about Java ME? I think that I do not avoid a typical GUI this time.

    I use Java ME platform SDK 3.0. btw when I see this environment which is very similar to the netbeans I feel a bit lost and dizzy.

    The first thing I thought is to build the simplest of programms, printing a line of a text, and attempt to modify this into my needs.

    The platform provides this source for you ( HelloMIDlet.java )
    package hello;
     
    import javax.microedition.midlet.*;
    import javax.microedition.lcdui.*;
     
    public class HelloMIDlet extends MIDlet implements CommandListener {
     
        private Command exitCommand; // The exit command
        private Display display;     // The display for this MIDlet
     
        public HelloMIDlet() {
            display = Display.getDisplay(this);
            exitCommand = new Command("Exit", Command.EXIT, 0);
        }
     
        public void startApp() {
     
            TextBox t = new TextBox("Hello", "Hello World!", 256, 0);
     
     
            t.addCommand(exitCommand);
            t.setCommandListener(this);
     
            display.setCurrent(t);
        }
     
        public void pauseApp() {
        }
     
        public void destroyApp(boolean unconditional) {
        }
     
        public void commandAction(Command c, Displayable s) {
            if (c == exitCommand) {
                destroyApp(false);
                notifyDestroyed();
            } 
        }
     
    }

    which is built and run fine in the cell phone.

    I assume that I leave the pauseApp and destroyApp methods untouched.

    So I have to modify the startApp method.

    I got the meaning of the arguments of the command
    TextBox t = new TextBox("Hello", "Hello World!", 256, 0);
    first = title of the textbox
    second = text which is printed
    third = number of chars allowed
    fourth = type constraints

    and... I stuck! I don't know what to do further.


    I would like some plain guidance as a beginning.

    Thank you in advance!


  2. #2
    Junior Member ordinarypeople's Avatar
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    Default Re: java me how to: input - math operation - output

    there are lot of tutorial of java me in the internet, just try googling it...

    at first coding with j2me, make me feel a bit dizzy too, but somehow i manage it
    its not simple n easy as java se , cmiiw

    maybe this will help u

    /*
     * To change this template, choose Tools | Templates
     * and open the template in the editor.
     */
     
    package dodol;
     
    import javax.microedition.lcdui.Command;
    import javax.microedition.lcdui.CommandListener;
    import javax.microedition.lcdui.Display;
    import javax.microedition.lcdui.Displayable;
    import javax.microedition.lcdui.Form;
    import javax.microedition.lcdui.TextField;
    import javax.microedition.midlet.*;
     
    /**
     * @author OP
     */
     
    public class Midlet extends MIDlet implements CommandListener {
     
    //variable declaration
     
        public static int num1, num2, add;
        public static  Form form;
        public static TextField text1, text2;
        public static Command hitung, exit, back;
        public static Display display;
     
        public Midlet()
        {
                 display = Display.getDisplay(this); //display for displaying all output
     
        }
        public void startApp() {
            itung(); // sum function
     
        }
     
        public void pauseApp() {
        }
     
        public void destroyApp(boolean unconditional) {
        }
     
     
    public void itung()
    {
     
       //all constructor
        Midlet.form = new Form("hitung"); 
     
        Midlet.text1 = new TextField("number 1", null, 30,TextField.NUMERIC);
        Midlet.text2 = new TextField("number 2", null, 30,TextField.NUMERIC);
        Midlet.hitung = new Command("hitung", Command.OK, 2);
        Midlet.exit = new Command("exit", Command.EXIT, 1);
        Midlet.back = new Command("back", Command.OK, 1);
     
     
        Midlet.form.deleteAll(); //delete all component if exist 
        Midlet.form.append(text1);
        Midlet.form.append(text2);
     
     
        Midlet.form.addCommand(Midlet.hitung);
        Midlet.form.addCommand(Midlet.exit);
        Midlet.form.setCommandListener(this); //set command listener
        Midlet.display.setCurrent(form); //displaying output from form
    }
     
    public void komanhitung()
    {
        int a = Integer.parseInt(Midlet.text1.getString());
        int b = Integer.parseInt(Midlet.text2.getString());
     
        int temp = a + b;
        String temp2 = Integer.toString(temp);
     
        Midlet.form.deleteAll();
        Midlet.form.append("total of "+Midlet.text1.getString()+" + "+Midlet.text2.getString()+" = "+temp2);
     
        Midlet.form.addCommand(Midlet.back);
        Midlet.form.addCommand(Midlet.exit);
        Midlet.form.setCommandListener(this);
        Midlet.display.setCurrent(form);
    }
     
    //all event command in here
        public void commandAction(Command c, Displayable d) {
             if (c == exit){
                /*exit aplikasi*/
                destroyApp(true);
    	    notifyDestroyed();
             }
             else if (c == hitung)
             {
              komanhitung();
             }
             else if (c == back)
             {
             itung();
             }else
            throw new UnsupportedOperationException("Not supported yet.");
        }
     
    }
    ow sorry for my bad english
    Last edited by ordinarypeople; April 4th, 2010 at 12:47 PM.
    Uncaught exception: MYBRAIN.lang.NullPointerException 0.

  3. #3
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    Default Re: java me how to: input - math operation - output

    ordinarypeople, thanks for your post!

    I did a lot of searching over the net, but didn't find something exact for my need.

    So I decided to study java ( again ) and midlets almost from scratch! Class by class ( display, displayable, form, command etc. ) and method by method.

    The studying goes well, I managed to get comfortable with the j2me platform and the samples I create from now on usually run fine!

    I haven't solved my trouble yet, but I think I get close. I won't give way to temptation of using your code for now and I 'll keep it in mind if I stick again.

    Thanks a lot anyway!

  4. #4
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    Thumbs up Re: java me how to: input - math operation - output

    finally! I found a solution to my trouble.

    I provide a piece of code:

     
    // This is a sample app which deals with monetary values, money
    // so all variables are of integer type ( a basic rule to avoid the unpredictable, fatal rounding of floats' fractional part )
    //they are used in pairs  to create a price - integer part ( int ) . fractional part ( int ) --->( edit ) WRONG! *
    // * ---> It prints incorrectly the less than 10 cents. ( eg. 100 euros and 5 cents = 100.5 --> error )
    // FIX: String pointZero = numC < 10 ? ".0" : "." ; ----> 100 euros and 5 cents --> numE + pointZero + numC
     
     
    import javax.microedition.midlet.*;
    import javax.microedition.lcdui.*;
     
    /*
     * @author Lifer
     */
     
    public class TheClass extends MIDlet implements CommandListener
    {
     
    	Form theForm = new Form ( "TheClass" );	// create a Form that contains Items 
                                                                             // for entering the fund information
    									// initialize the variable at its declaration because
                                                                            // it has no dependencies from constructor parameters
     
    	// all input here
    	TextField priceE = new TextField( "Mixed Price\nEuros:", "", 7, TextField.NUMERIC );	 // numeric, no need of mixed string type
    	TextField priceC = new TextField( "Cents:", "00", 2, TextField.NUMERIC );
     
    	TextField vat = new TextField( "Value Added Tax ( 0 - 100%): ", "", 3, TextField.NUMERIC );
     
     
    		// creation of 2 buttons. one for calculation and one for exit
    		static final Command calcCommand = new Command ("Calc", Command.OK, 1 );		
    		static final Command exitCommand = new Command ("Exit", Command.EXIT, 1 );
     
    	Display display = Display.getDisplay( this );	  // addition of a variable storing the Display instance for application
     
    	public TheClass ()		// constructor. it contains all the variables created above
    	{
     
    		theForm.append ( priceE );
    		theForm.append ( priceC );
    		theForm.append ( vat );
     
    			theForm.addCommand ( calcCommand );
    			theForm.addCommand ( exitCommand );
    			theForm.setCommandListener ( this );
     
    	}
     
    	// create method calc which does all the work
    	public void calc ()
    	{
    		Alert alert = new Alert ("Calc");
     
    		int price2E = Integer.parseInt( priceE.getString() );	// for example 100 euros
    		int price2C = Integer.parseInt( priceC.getString() );	// and 50 cents
    		int price = price2E * 100 + price2C;				// stored in "price" as an integer: 10050
     
    		int vat2 = Integer.parseInt( vat.getString() );		// stores the tax, eg 21%
     
    		int tax_free = price * 100 / ( 100 + vat2 );	// instead of dividing with 21% ( 0.21 ) and messing
    										// messing with floats, I "divide" via multiply ( * 100 / 121 )
     
    		int tax_freeE = tax_free / 100;		// integer part of tax free price ( euros )
    		int tax_freeC = tax_free % 100;		// fractional part ( cents )
     
                   String tax_freeP = tax_freeC < 10 ? ".0" : "." ;   // EDIT2: fix less-than-10-cents presentation error
     
     
    				  alert.setString ( "tax free price: " + tax_freeE + tax_freeP + tax_freeC + " Euros" );	// all output here 
                             // edit1: avoid alert.setString ( "tax free price: " + tax_freeE +"." + tax_freeC ); --> false result when tax_freeC < 10
    				  alert.setTimeout ( Alert.FOREVER );	// the display alert screen stays forever, 
    				  display.setCurrent (alert);			// and not for limited time unless I press button 
     
    	}
     
     
    				// actions of our 2 buttons
    				public void commandAction (Command c, Displayable d)
    				{
    					if (c == exitCommand)
    					{
    						notifyDestroyed();
    					}
    					else if (c == calcCommand)
    					{
    						calc ();
    					}
    				}
     
    	// leave this part as it is
        public void startApp()
    	{
    		display.setCurrent ( theForm ); // only remember to add correctly the name of the Form variable
        }
     
        public void pauseApp()
            {}
     
        public void destroyApp(boolean unconditional)
    	{}
     
    }

    This is a sample code of the app i created. Nothing special for pros, yet of great value to me, as I started to become familiar with the MIDlets, their buttons, commands etc etc.

    I haven't compiled this piece, if there is sth wrong here, please comment. ( whoever might be interested )
    Last edited by Lifer; April 23rd, 2010 at 04:35 AM. Reason: to improve code

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