java me how to: input - math operation - output

**Lifer** · March 31st, 2010, 10:17 AM

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!

**ordinarypeople** · April 4th, 2010, 11:11 AM

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

**Lifer** · April 4th, 2010, 11:37 AM

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!

**Lifer** · April 7th, 2010, 05:36 PM

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 )

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

LinkBack

Thread Tools

Display

java me how to: input - math operation - output

Related threads:

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

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

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

Similar Threads

Output String Handling in Java

Simple Input/Output program Acting weird

Operation ==

Math in Java?

Redirect error and output stream using java program