Calculator without a decimal point

**r035198x** · Jan 23 '07, 06:06 AM

Sorry Texas for the late reply. You were previously dealing with integers(withou t the decimal point).
To capture integers Integer.parseIn t was used which was adequate. When you added the decimal point, Integer.parseIn t was no longer sufficient. You now need Double.parseDou ble and change your variables from int type to double type. I have made these changes below.

Code:

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;

public class Calculator extends JFrame implements ActionListener {
	private JTextField displayText = new JTextField(30);
    private JButton[] button = new JButton[20];
    private String[] keys = {"7", "8", "9", "/",
                            "4", "5", "6", "*",
                            "1", "2", "3", "-",
                            "0", "C", "=", "+",
			    ".", " ", " ", " "};
    private String numStr1 = "";
    private String numStr2 = "";
    private char op;
    private boolean firstInput = true;
    public Calculator() {
		setTitle("My Calculator");
        setSize(230, 250);
        Container pane = getContentPane();
        pane.setLayout(null);
        displayText.setSize(200, 30);
        displayText.setLocation(10, 10);
        pane.add(displayText);
        int x, y;
        x = 10;
        y = 40;
        for (int ind = 0; ind < 20; ind++) {
			button[ind] = new JButton(keys[ind]);
            button[ind].addActionListener(this);
            button[ind].setSize(50, 30);
            button[ind].setLocation(x, y);
            pane.add(button[ind]);
            x = x + 50;
            if((ind + 1) % 4 == 0) {
                x = 10;
                y = y + 30;
            }
        }

        this.addWindowListener(new WindowAdapter() {
			public void windowClosing(WindowEvent e) {
				System.exit(0);
            }
        });

        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

    public void actionPerformed(ActionEvent e) {
        String resultStr;                                   //Step 1
        String str = String.valueOf(e.getActionCommand());  //Steps 1 and 2
        char ch = str.charAt(0);                            //Steps 1 and 3
        switch (ch)                                          //Step 4
        {
        case '0': case '1': case '2':                       //Step 4a
        case '3': case '4': case '5':
        case '6': case '7': case '8':
        case '9': case '.':if (firstInput)
                  {
                     numStr1 = numStr1 + ch;
                     displayText.setText(numStr1);
                  }
                  else
                  {
                      numStr2 = numStr2 + ch;
                      displayText.setText(numStr2);
                  }
                  break;
        case '+': case '-': case '*':                       //Step 4b
        case '/': op = ch;
                  firstInput = false;
                  break;
        case '=': resultStr = evaluate();                   //Step 4c
                  displayText.setText(resultStr);
                  numStr1 = resultStr;
                  numStr2 = "";
                  firstInput = false;
                  break;
        case 'C': displayText.setText("");                  //Step 4c
                  numStr1 = "";
                  numStr2 = "";
                  firstInput = true;
        }
    }

    private String evaluate()
    {
        final char beep = '\u0007';

        try
        {
            double num1 = Double.parseDouble(numStr1);// Changed here
            double num2 = Double.parseDouble(numStr2);//
            double result = 0;

            switch (op)
            {
            case '+': result = num1 + num2;
                      break;
            case '-': result = num1 - num2;
                      break;
            case '*': result = num1 * num2;
                      break;
            case '/': result = num1 / num2;
            }

            return String.valueOf(result);
        }
        catch(ArithmeticException e)
        {
            System.out.print(beep);
            return "E R R O R: " + e.getMessage();
        }
        catch(NumberFormatException e)
        {
            System.out.print(beep);
            if (numStr1.equals(""))
               return "E R R O R: Invalid First Number" ;
            else
               return "E R R O R: Invalid Second Number" ;
        }
        catch(Exception e)
        {
            System.out.print(beep);
            return "E R R O R";
        }
    }

    public static void main(String[] args)
    {
        Calculator C = new Calculator();
    }
}

**TexasNewbie** · Jan 23 '07, 03:30 PM

I cant believe that it was something that I overlooked. A special thanks to r035198x, for not only looking over the code, but for helping me out.

**r035198x** · Jan 23 '07, 03:37 PM

Originally posted by TexasNewbie

I cant believe that it was something that I overlooked. A special thanks to r035198x, for not only looking over the code, but for helping me out.

Just post any Java problems you get anytime. The guys here are always willing to help.

**TexasNewbie** · Jan 24 '07, 07:43 PM

further problem now I am getting infinity if I divide by zero. The exception should have caught it and given it an error : / by zero. Now, what have I forgotten?

**DeMan** · Jan 24 '07, 08:53 PM

In your evaluate() method, if the op is division, you should check that num2 != 0.0 (the program does not do this check for you because it is not an invalid number on parsing). you can do something like:

Code:

if(num2 == 0.0)
{
  throw new ArithmeticException("Can't Divide by 0");
}

**r035198x** · Jan 25 '07, 05:28 AM

Originally posted by TexasNewbie

further problem now I am getting infinity if I divide by zero. The exception should have caught it and given it an error : / by zero. Now, what have I forgotten?

Tricky one for you this.

Now dividing by (double) 0.0 does not cause an exception. The result is simply Infinity. This is because double are approximations and not exact values so 0.0 is a number as close to zero as possible....

Dividing by (int) 0 is the one that throws the / by zero exception.

**TexasNewbie** · Jan 25 '07, 03:24 PM

Originally posted by r035198x

Tricky one for you this.

Now dividing by (double) 0.0 does not cause an exception. The result is simply Infinity. This is because double are approximations and not exact values so 0.0 is a number as close to zero as possible....

Dividing by (int) 0 is the one that throws the / by zero exception.

Now I'm really confused as to were I would insert the Dividing by (int) 0 or were I would put the throw exception to make this happen? I have tried install it in several places in the code and all I get is error after error. I'm really lost here!

**r035198x** · Jan 25 '07, 03:41 PM

Originally posted by TexasNewbie

Now I'm really confused as to were I would insert the Dividing by (int) 0 or were I would put the throw exception to make this happen? I have tried install it in several places in the code and all I get is error after error. I'm really lost here!

Code:

double num1 = Double.parseDouble(numStr1);// Changed here
double num2 = Double.parseDouble(numStr2);//
double result = 0;

These lines of code guarantee that you are never going to get a / by zero exception because you are now operating on doubles which give Infinity on / by zero rather than on ints which give that exception.

If you want to stop the program from getting infinity as a result then test the result with

Code:

if((result == Double.POSITIVE_INFINITY) || (result == Double.NEGATIVE_INFINITY)) {
        System.out.println("error");
e.t.c
}

**TexasNewbie** · Jan 25 '07, 06:09 PM

Okay, I put the statement were thought it should go but it still comes up infinity, any other hints clues suggestions? Or am I just an idiot? See below

import javax.swing.*;
import java.awt.*;
import java.awt.event. *;
import java.io.*;

public class Calculator extends JFrame implements ActionListener {
private JTextField displayText = new JTextField(30);
private JButton[] button = new JButton[20];
private String[] keys = {"7", "8", "9", "/",
"4", "5", "6", "*",
"1", "2", "3", "-",
"0", "C", "=", "+",
".", " ", " ", " "};
private String numStr1 = "";
private String numStr2 = "";
private char op;
private boolean firstInput = true;
public Calculator() {
setTitle("My Calculator");
setSize(230, 250);
Container pane = getContentPane( );
pane.setLayout( null);
displayText.set Size(200, 30);
displayText.set Location(10, 10);
pane.add(displa yText);
int x, y;
x = 10;
y = 40;
for (int ind = 0; ind < 20; ind++) {
button[ind] = new JButton(keys[ind]);
button[ind].addActionListe ner(this);
button[ind].setSize(50, 30);
button[ind].setLocation(x, y);
pane.add(button[ind]);
x = x + 50;
if((ind + 1) % 4 == 0) {
x = 10;
y = y + 30;
}
}

this.addWindowL istener(new WindowAdapter() {
public void windowClosing(W indowEvent e) {
System.exit(0);
}
});

setVisible(true );
setDefaultClose Operation(EXIT_ ON_CLOSE);
}

public void actionPerformed (ActionEvent e) {
String resultStr; //Step 1
String str = String.valueOf( e.getActionComm and()); //Steps 1 and 2
char ch = str.charAt(0); //Steps 1 and 3
switch (ch) //Step 4
{
case '0': case '1': case '2': //Step 4a
case '3': case '4': case '5':
case '6': case '7': case '8':
case '9': case '.':if (firstInput)
{
numStr1 = numStr1 + ch;
displayText.set Text(numStr1);
}
else
{
numStr2 = numStr2 + ch;
displayText.set Text(numStr2);
}
break;
case '+': case '-': case '*': //Step 4b
case '/': op = ch;
firstInput = false;
break;
case '=': resultStr = evaluate(); //Step 4c
displayText.set Text(resultStr) ;
numStr1 = resultStr;
numStr2 = "";
firstInput = false;
break;
case 'C': displayText.set Text(""); //Step 4c
numStr1 = "";
numStr2 = "";
firstInput = true;
}
}

private String evaluate()
{
final char beep = '\u0007';

try
{
double num1 = Double.parseDou ble(numStr1);
double num2 = Double.parseDou ble(numStr2);
double result = 0;
if((result == Double.POSITIVE _INFINITY) || (result == Double.NEGATIVE _INFINITY))
{
System.out.prin tln("error");

}
switch (op)
{
case '+': result = num1 + num2;
break;
case '-': result = num1 - num2;
break;
case '*': result = num1 * num2;
break;
case '/': result = num1 / num2;
}

return String.valueOf( result);
}
catch(Arithmeti cException e)
{
System.out.prin t(beep);
return "E R R O R:" + e.getMessage();
}
catch(NumberFor matException e)
{
System.out.prin t(beep);
if (numStr1.equals (""))
return "E R R O R: Invalid First Number" ;
else
return "E R R O R: Invalid Second Number" ;
}
catch(Exception e)
{
System.out.prin t(beep);
return "E R R O R";
}
}

public static void main(String[] args)
{
Calculator C = new Calculator();
}
}

**r035198x** · Jan 25 '07, 07:15 PM

Makes sense to put it after the result is calculated

Code:

switch (op)
            {
            case '+': result = num1 + num2;
                      break;
            case '-': result = num1 - num2;
                      break;
            case '*': result = num1 * num2;
                      break;
            case '/': result = num1 / num2;
            }
}
if((result == Double.POSITIVE_INFINITY) || (result == Double.NEGATIVE_INFINITY))
{
System.out.println("error");
return "E R R O R:" 
}
else {
       return String.valueOf(result);
}
        }
        catch(ArithmeticException e)
        {
            System.out.print(beep);	
            + e.getMessage();
	}

P.S Use code tags for posting code

**TexasNewbie** · Jan 25 '07, 09:06 PM

private String evaluate()
{
final char beep = '\u0007';

try
{
double num1 = Double.parseDou ble(numStr1);
double num2 = Double.parseDou ble(numStr2);
double result = 0;

switch (op)
{
case '+': result = num1 + num2;
break;
case '-': result = num1 - num2;
break;
case '*': result = num1 * num2;
break;
case '/': result = num1 / num2;
}
if ((result == Double.POSITIVE _INFINITY) || (result == Double.NEGATIVE _INFINITY))
{
System.out.prin t(beep);
return "E R R O R:";
}
else
return String.valueOf( result);
}
catch(Arithmeti cException e)
{
System.out.prin t(beep);
}
catch(NumberFor matException e)
{
System.out.prin t(beep);
if (numStr1.equals (""))
return "E R R O R: Invalid First Number" ;
else
return "E R R O R: Invalid Second Number" ;
}
catch(Exception e)
{
System.out.prin t(beep);
return "E R R O R";
}
finally
{
Calculator C = new Calculator();
}
} //line 153 this is the close for try
//line 154
} //line 155 this is te close for privat string

Okay, I am about as frustrated with this thing as I can be. I went back to the book thinking that there had to be a finally statement, but that didn't work I keep getting a missing return statement on line 153

**DeMan** · Jan 25 '07, 10:35 PM

I Don't remember exactly how exceptions work, but I think your "finally" block is incorrect - can the code ever get here? (I think the compiler expects you to return a value here, which would be a fix, but I think the code will never reach this point so you should delete it).

Basically the "finally" is executed irrespective of which exception is thrown, but all of your exceptions have a return line which will stop execution of that method before it gets to finally.....

**Ganon11** · Jan 25 '07, 10:50 PM

Originally posted by TexasNewbie

Code:

        catch(ArithmeticException e)
          {
          System.out.print(beep);	
          }

This catch() block has no return statement, so it is possible that there will not be a return - this is why you get an error. Perhaps you should add the line

Code:

return "E R R O R";

as you have in other blocks.

**TexasNewbie** · Jan 26 '07, 04:22 AM

I would like to thank everyone for thier input and let you know that I have resolved all issues with this project. New one to come soon. Expect to hear more from me. Thanks again.

Calculator without a decimal point

Calculator without a decimal point

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