Calculator without a decimal point

[TexasNewbie]

This was originally just a calculator without a decimal point. After I added the decimal, it now tells me invalid second number.

//GUI Calculator Program
 
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
        {
            int num1 = Integer.parseInt(numStr1);
            int num2 = Integer.parseInt(numStr2);
            int 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();
    }
}

Please Help

[r035198x]

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.

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]

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]

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]

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]

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:

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

[r035198x]

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]

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]

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!

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

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

[TexasNewbie]

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();
}
}