So I'm making a Java Calculator and walking into some errors upon clicking the function buttons (it compiles perfectly fine though). The error on the 1st line in my CMD was a NumberFormat Exception. After some searching I figured out that somewhere in my code I was trying to get a double out of an empty string (basically what I'm trying to do is parse a double from the label text). I'm guessing it's this part:
// if statement that puts the labels text into the first or second number
if(firstNumber)
{
number1 = Double.parseDouble(label.getText().trim());
} else {
number2 = Double.parseDouble(label.getText().trim());
}
Basically the problems are when i push the / * + or - button i get a NumberFormatExeption: For input string "/" etc. I can't quite figure out how i have to fix this error (I'm still (somewhat) a beginner in Java). Further down the line of errors (there were quite alot) were a whole lot of errors I didn't understand such as EventDispatchThread, EventQueue and many others. I couldn't find an explanation on my level of experience either so I'm asking for help here.
The numeric buttons all work fine.
At run: [http://gyazo.com/71cb4dde449ccf7ece44017388a71a0f]
Putting in numbers: [http://gyazo.com/5c7ab6c54ac6da180845c66866d66f8f]
All other buttons give errors in my CMD.
Here's my code (the spacing might be messed up in some parts):
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
// import for Nimbus look
import javax.swing.UIManager.*;
public class Calculator extends JFrame implements ActionListener
{
private JPanel bottom = new JPanel(); private JPanel top = new JPanel();
private JLabel label = new JLabel(" ");
private JButton[] buttons = new JButton[16];
// booleans for calculator functions
boolean add = false, substract = false, devide = false, multiply = false, firstNumber = true;
// numbers that will be calculated
double number1, number2;
public Calculator()
{
setLayout(new BoxLayout(getContentPane(), BoxLayout.PAGE_AXIS));
// bottom panel
bottom.setPreferredSize(new Dimension(100,100));
bottom.setLayout(new BorderLayout());
//add bottom panel to frame
add(bottom);
// top panel
top.setPreferredSize(new Dimension(300,400));
top.setLayout(new GridLayout(4,4,3,3));
top.setBackground(Color.BLACK);
//dont add top panel to frame: you want top to be on bottom
// add top panel to bottom panel
bottom.add(top);
// label
label.setFont(new Font("Courier", Font.PLAIN, 20));
label.setBackground(Color.BLACK);
label.setForeground(Color.WHITE);
label.setHorizontalAlignment(SwingConstants.RIGHT); // text is right-aligned
label.setOpaque(true);
// add the label to the bottom panel
bottom.add(label, BorderLayout.NORTH);
// creating buttons
for(int i = 0; i < buttons.length; i++)
{
buttons[i] = new JButton("789/456*123+c0=-".substring(i, i+1));
buttons[i].addActionListener(this);
// add them to the top panel
top.add(buttons[i]);
}
// Nimbus look
try {
for (LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) {
if ("Nimbus".equals(info.getName())) {
UIManager.setLookAndFeel(info.getClassName());
break;
}
}
} catch (Exception e) {
// If Nimbus is not available, you can set the GUI to another look and feel.
//set to default somehow o.o
}
// frame setters
setTitle("Calculator");
setSize(400,400);
setVisible(true);
setResizable(false);
setDefaultCloseOperation(EXIT_ON_CLOSE);
}
public void Clear()
{
label.setText(" ");
}
@Override
public void actionPerformed(ActionEvent e)
{
//if's for all function buttons
if(e.getSource() == buttons[3])
{
// devide
devide = true;
substract = false;
add = false;
multiply = false;
firstNumber = false;
Clear();
label.setText("/");
}
if(e.getSource() == buttons[7])
{
// multiply
multiply = true;
substract = false;
devide = false;
add = false;
firstNumber = false;
Clear();
label.setText("*");
}
if(e.getSource() == buttons[11])
{
// add
add = true;
substract = false;
devide = false;
multiply = false;
firstNumber = false;
Clear();
label.setText("+");
}
if(e.getSource() == buttons[12])
{
// clear
label.setText("0");
number1 = 0.00;
number2 = 0.00;
add = false;
substract = false;
devide = false;
multiply = false;
firstNumber = true;
Clear();
}
if(e.getSource() == buttons[15])
{
// substract
substract = true;
add = false;
devide = false;
multiply = false;
firstNumber = false;
Clear();
label.setText("-");
}
// for loops that add the numbers on the buttons to the label
for(int i = 0; i < 3; i++)
{
if(e.getSource() == buttons[i])
{
if(label.getText() == "0")
{
label.setText("");
label.setText(label.getText() + buttons[i].getText());
} else {
label.setText(label.getText() + buttons[i].getText());
}
}
}
for(int i = 4; i < 7; i++)
{
if(e.getSource() == buttons[i])
{
if(label.getText() == "0")
{
label.setText("");
label.setText(label.getText() + buttons[i].getText());
} else {
label.setText(label.getText() + buttons[i].getText());
}
}
}
for(int i = 8; i < 11; i++)
{
if(e.getSource() == buttons[i])
{
if(label.getText() == "0")
{
label.setText("");
label.setText(label.getText() + buttons[i].getText());
} else {
label.setText(label.getText() + buttons[i].getText());
}
}
}
for(int i = 13; i < 14; i++)
{
if(e.getSource() == buttons[i])
{
if(label.getText() == "0")
{
label.setText("");
label.setText(label.getText() + buttons[i].getText());
} else {
label.setText(label.getText() + buttons[i].getText());
}
}
}
// if statement that puts the labels text into the first or second number
if(firstNumber)
{
number1 = Double.parseDouble(label.getText().trim());
} else {
number2 = Double.parseDouble(label.getText().trim());
}
// calculation
if(e.getSource() == buttons[14])
{
// calculate
if(devide){number1 = ((double)(number1) / (double)(number2)); }
if(multiply){number1 = ((double)(number1) * (double)(number2)); }
if(add){number1 = ((double)(number1) + (double)(number2)); }
if(substract){number1 = ((double)(number1) - (double)(number2)); }
label.setText(Double.toString(number1));
}
}
public static void main(String[] args)
{
new Calculator();
}
}
Lastly, the calculations made by the calculator are incorrect. I also can't wrap my head around what's causing that. Please bear in mind that I'm a beginner at Java and this is my first question on stackoverflow. Thanks in advance for helping me, whoever will :)
UPDATE: i fixed the errors by putting my code as follows:
if(e.getSource() == buttons[15])
{
// substract
substract = true;
add = false;
devide = false;
multiply = false;
firstNumber = false;
isNumberKey = false;
if(isNumberKey)
{
if(firstNumber)
{
label.setText(label.getText().replace("/",""));
label.setText(label.getText().replace("*",""));
label.setText(label.getText().replace("+",""));
label.setText(label.getText().replace("-",""));
number1 = Double.parseDouble(label.getText().trim());
} else {
label.setText(label.getText().replace("/",""));
label.setText(label.getText().replace("*",""));
label.setText(label.getText().replace("+",""));
label.setText(label.getText().replace("-",""));
number2 = Double.parseDouble(label.getText().trim());
}
}
Clear();
label.setText("-");
}
All i need to do now is fix the calculations... Thanks for the help everyone!
Cannot delve totaly into your logic there, but here's some hints:
First, you don't have to guess where the error is. In case of uncaught exception like here, thread that produced it will print it's stack trace to console. It looks like this:
Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: "/"
at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:1222)
at java.lang.Double.parseDouble(Double.java:510)
at mypackage.Calculator.actionPerformed(Calculator.java:229)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6297)
From here you see that exception happened in thread named AWT-EventQueue-0, which is swing's standard event dispatching thread (all GUI applications handles events in single thread). Another thing you search in stack trace is to find what line in your code thrown it. Here it's the line:
at mypackage.Calculator.actionPerformed(Calculator.java:229)
In source, it is line:
number2 = Double.parseDouble(label.getText().trim());
, so you guessed right. What you can do is add another boolean there which will be set only if number button is hit, and then change that part of code to something like:
if( isNumber){
if(firstNumber)
{
number1 = Double.parseDouble(label.getText().trim());
} else {
number2 = Double.parseDouble(label.getText().trim());
}
}Apart from that, instead of using multiple boolean flags for operation, use Java enum type
enum Operation {devide, substract, add, multiply};
your code will be more readable and "java" styled. Good starting point, just go ahead!