Calculator Program Using Java AWT and Swing

In this piece, let's build a simple GUI calculator application using Java AWT and Swing.

Java AWT is a toolkit that helps us build a GUI for a Java program. Swing provides a more sophisticated set of components, and can be seen as an upgrade to AWT.

The application we are building will support addition, subtraction, multiplication, and division operations. It will provide the user with ten digits -- 0 through 9 -- to perform the operations on.

Additionally, the user can clear the display box with a Clear button provided.

Now lets begin coding!

First, we import the necessary packages for AWT, Swing, and AWT's event handling mechanism.

Then, we enumerate the available operators.

	import java.awt.*;
	import javax.swing.*;
	import java.awt.event.*;
	enum Operator {
	PLUS,
	MINUS,
	TIMES,
	DIVIDE
	}

view raw ImportCalculator.java hosted with ❤ by GitHub

Then, we create the Calculator class. We will need to handle the button-press events, so the class should implement the ActionListener interface.

public class Calculator implements ActionListener {}

view raw CalculatorStructure.java hosted with ❤ by GitHub

Next, we define and initialize several instance variables for the class, including the application frame, result box, control button, number buttons, etc.

We also instantiate the Calculator class from the main method.

	/* Application Frame */
	JFrame frame = new JFrame("Calculator by Roshan");
	/* Result Box */
	JTextField result = new JTextField(20);
	/* Control Buttons */
	JButton addBtn = new JButton("+");
	JButton subtractBtn = new JButton("-");
	JButton multiplyBtn = new JButton("x");
	JButton divideBtn = new JButton("%");
	JButton equalBtn = new JButton("=");
	JButton clearBtn = new JButton("C");
	/* Number Buttons */
	JButton zeroBtn = new JButton("0");
	JButton oneBtn = new JButton("1");
	JButton twoBtn = new JButton("2");
	JButton threeBtn = new JButton("3");
	JButton fourBtn = new JButton("4");
	JButton fiveBtn = new JButton("5");
	JButton sixBtn = new JButton("6");
	JButton sevenBtn = new JButton("7");
	JButton eightBtn = new JButton("8");
	JButton nineBtn = new JButton("9");
	/* Other instance variables */
	int operand1 = 0, operand2 = 0, resultNum = 0;
	Operator operator;
	public static void main(String[] args) {
	new Calculator();
	}

view raw InitializeInstanceVariables.java hosted with ❤ by GitHub

You may like these posts

• Multicasting Events in Java
• Calculator Program Using Java AWT and Swing

Inside the no-arguments constructor for the class, we can set the frame properties, position the various UI elements within the frame, and finally add those elements to the frame.

Then, to react to the button presses, we attach event listeners to each of the elements. Since the Calculator class itself implements the ActionListener interface, we can attach the class itself by using the this keyword.

	public Calculator() {
	/* Set frame properties */
	frame.setVisible(true);
	frame.setSize(350, 500);
	frame.setLayout(null);
	frame.setBackground(Color.gray);
	/* Set bounds to objects in the frame */
	result.setBounds(20, 50, 300, 40);
	sevenBtn.setBounds(55, 100, 50, 50);
	eightBtn.setBounds(115, 100, 50, 50);
	nineBtn.setBounds(175, 100, 50, 50);
	clearBtn.setBounds(235, 100, 50, 50);
	fourBtn.setBounds(55, 180, 50, 50);
	fiveBtn.setBounds(115, 180, 50, 50);
	sixBtn.setBounds(175, 180, 50, 50);
	addBtn.setBounds(235, 180, 50, 50);
	oneBtn.setBounds(55, 260, 50, 50);
	twoBtn.setBounds(115, 260, 50, 50);
	threeBtn.setBounds(175, 260, 50, 50);
	subtractBtn.setBounds(235, 260, 50, 50);
	zeroBtn.setBounds(55, 340, 50, 50);
	multiplyBtn.setBounds(115, 340, 50, 50);
	divideBtn.setBounds(175, 340, 50, 50);
	equalBtn.setBounds(235, 340, 50, 50);
	/* Add objects to the frame */
	frame.add(result);
	frame.add(sevenBtn);
	frame.add(eightBtn);
	frame.add(nineBtn);
	frame.add(clearBtn);
	frame.add(fourBtn);
	frame.add(fiveBtn);
	frame.add(sixBtn);
	frame.add(addBtn);
	frame.add(oneBtn);
	frame.add(twoBtn);
	frame.add(threeBtn);
	frame.add(subtractBtn);
	frame.add(zeroBtn);
	frame.add(multiplyBtn);
	frame.add(divideBtn);
	frame.add(equalBtn);
	/* Attach event listeners */
	sevenBtn.addActionListener(this);
	eightBtn.addActionListener(this);
	nineBtn.addActionListener(this);
	fourBtn.addActionListener(this);
	fiveBtn.addActionListener(this);
	sixBtn.addActionListener(this);
	oneBtn.addActionListener(this);
	twoBtn.addActionListener(this);
	threeBtn.addActionListener(this);
	zeroBtn.addActionListener(this);
	clearBtn.addActionListener(this);
	addBtn.addActionListener(this);
	subtractBtn.addActionListener(this);
	multiplyBtn.addActionListener(this);
	divideBtn.addActionListener(this);
	equalBtn.addActionListener(this);
	}

view raw NoArgConstructor.java hosted with ❤ by GitHub

Next, we need to override the actionPerformed method.

Since the Calculator class is assigned as the action listener for each of the buttons, whenever an action event occurs, the actionPerfomed method is invoked.

Inside the actionPerformed method, we find the source of the event, cast it to a JButton instance, and respond accordingly.

For example, if the button was the addBtn button for addition, we initialize the operator instance variable and set it as Operator.PLUS.

If the button was the equalBtn for computing the result, we calculate the result number depending on the value of the operator variable set prior, and display the number on the result box.

	@Override
	public void actionPerformed(ActionEvent event) {
	JButton eventSourceBtn = (JButton) event.getSource();
	if (eventSourceBtn == addBtn) {
	operand1 = Integer.parseInt(result.getText());
	operator = Operator.PLUS;
	result.setText("");
	} else if (eventSourceBtn == subtractBtn) {
	operand1 = Integer.parseInt(result.getText());
	operator = Operator.MINUS;
	result.setText("");
	} else if (eventSourceBtn == multiplyBtn) {
	operand1 = Integer.parseInt(result.getText());
	operator = Operator.TIMES;
	result.setText("");
	} else if (eventSourceBtn == divideBtn) {
	operand1 = Integer.parseInt(result.getText());
	operator = Operator.DIVIDE;
	result.setText("");
	} else if (eventSourceBtn == clearBtn) {
	result.setText("0");
	} else if (eventSourceBtn == zeroBtn) {
	result.setText(result.getText() + "0");
	} else if (eventSourceBtn == oneBtn) {
	result.setText(result.getText() + "1");
	} else if (eventSourceBtn == twoBtn) {
	result.setText(result.getText() + "2");
	} else if (eventSourceBtn == threeBtn) {
	result.setText(result.getText() + "3");
	} else if (eventSourceBtn == fourBtn) {
	result.setText(result.getText() + "4");
	} else if (eventSourceBtn == fiveBtn) {
	result.setText(result.getText() + "5");
	} else if (eventSourceBtn == sixBtn) {
	result.setText(result.getText() + "6");
	} else if (eventSourceBtn == sevenBtn) {
	result.setText(result.getText() + "7");
	} else if (eventSourceBtn == eightBtn) {
	result.setText(result.getText() + "8");
	} else if (eventSourceBtn == nineBtn) {
	result.setText(result.getText() + "9");
	} else if (eventSourceBtn == equalBtn) {
	operand2 = Integer.parseInt(result.getText());
	switch (operator) {
	case PLUS:
	resultNum = operand1 + operand2;
	break;
	case MINUS:
	resultNum = operand1 - operand2;
	break;
	case TIMES:
	resultNum = operand1 * operand2;
	break;
	case DIVIDE:
	resultNum = operand1 / operand2;
	break;
	}
	result.setText(resultNum + "");
	}
	}

view raw ActionPerfomed.java hosted with ❤ by GitHub

With this, the application is complete.

The final program should look like the following.

	import java.awt.*;
	import javax.swing.*;
	import java.awt.event.*;
	enum Operator {
	PLUS,
	MINUS,
	TIMES,
	DIVIDE
	}
	public class Calculator implements ActionListener {
	/* Application Frame */
	JFrame frame = new JFrame("Calculator by Roshan");
	/* Result Box */
	JTextField result = new JTextField(20);
	/* Control Buttons */
	static JButton addBtn = new JButton("+");
	static JButton subtractBtn = new JButton("-");
	static JButton multiplyBtn = new JButton("x");
	static JButton divideBtn = new JButton("%");
	static JButton equalBtn = new JButton("=");
	static JButton clearBtn = new JButton("C");
	/* Number Buttons */
	static JButton zeroBtn = new JButton("0");
	static JButton oneBtn = new JButton("1");
	static JButton twoBtn = new JButton("2");
	static JButton threeBtn = new JButton("3");
	static JButton fourBtn = new JButton("4");
	static JButton fiveBtn = new JButton("5");
	static JButton sixBtn = new JButton("6");
	static JButton sevenBtn = new JButton("7");
	static JButton eightBtn = new JButton("8");
	static JButton nineBtn = new JButton("9");
	/* Other instance variables */
	int operand1 = 0, operand2 = 0, resultNum = 0;
	Operator operator;
	public static void main(String[] args) {
	new Calculator();
	}
	public Calculator() {
	/* Set frame properties */
	frame.setVisible(true);
	frame.setSize(350, 500);
	frame.setLayout(null);
	frame.setBackground(Color.gray);
	/* Set bounds to objects in the frame */
	result.setBounds(20, 50, 300, 40);
	sevenBtn.setBounds(55, 100, 50, 50);
	eightBtn.setBounds(115, 100, 50, 50);
	nineBtn.setBounds(175, 100, 50, 50);
	clearBtn.setBounds(235, 100, 50, 50);
	fourBtn.setBounds(55, 180, 50, 50);
	fiveBtn.setBounds(115, 180, 50, 50);
	sixBtn.setBounds(175, 180, 50, 50);
	addBtn.setBounds(235, 180, 50, 50);
	oneBtn.setBounds(55, 260, 50, 50);
	twoBtn.setBounds(115, 260, 50, 50);
	threeBtn.setBounds(175, 260, 50, 50);
	subtractBtn.setBounds(235, 260, 50, 50);
	zeroBtn.setBounds(55, 340, 50, 50);
	multiplyBtn.setBounds(115, 340, 50, 50);
	divideBtn.setBounds(175, 340, 50, 50);
	equalBtn.setBounds(235, 340, 50, 50);
	/* Add objects to the frame */
	frame.add(result);
	frame.add(sevenBtn);
	frame.add(eightBtn);
	frame.add(nineBtn);
	frame.add(clearBtn);
	frame.add(fourBtn);
	frame.add(fiveBtn);
	frame.add(sixBtn);
	frame.add(addBtn);
	frame.add(oneBtn);
	frame.add(twoBtn);
	frame.add(threeBtn);
	frame.add(subtractBtn);
	frame.add(zeroBtn);
	frame.add(multiplyBtn);
	frame.add(divideBtn);
	frame.add(equalBtn);
	/* Attach event listeners */
	sevenBtn.addActionListener(this);
	eightBtn.addActionListener(this);
	nineBtn.addActionListener(this);
	fourBtn.addActionListener(this);
	fiveBtn.addActionListener(this);
	sixBtn.addActionListener(this);
	oneBtn.addActionListener(this);
	twoBtn.addActionListener(this);
	threeBtn.addActionListener(this);
	zeroBtn.addActionListener(this);
	clearBtn.addActionListener(this);
	addBtn.addActionListener(this);
	subtractBtn.addActionListener(this);
	multiplyBtn.addActionListener(this);
	divideBtn.addActionListener(this);
	equalBtn.addActionListener(this);
	}
	@Override
	public void actionPerformed(ActionEvent event) {
	JButton eventSourceBtn = (JButton) event.getSource();
	if (eventSourceBtn == addBtn) {
	operand1 = Integer.parseInt(result.getText());
	operator = Operator.PLUS;
	result.setText("");
	} else if (eventSourceBtn == subtractBtn) {
	operand1 = Integer.parseInt(result.getText());
	operator = Operator.MINUS;
	result.setText("");
	} else if (eventSourceBtn == multiplyBtn) {
	operand1 = Integer.parseInt(result.getText());
	operator = Operator.TIMES;
	result.setText("");
	} else if (eventSourceBtn == divideBtn) {
	operand1 = Integer.parseInt(result.getText());
	operator = Operator.DIVIDE;
	result.setText("");
	} else if (eventSourceBtn == clearBtn) {
	result.setText("0");
	} else if (eventSourceBtn == zeroBtn) {
	result.setText(result.getText() + "0");
	} else if (eventSourceBtn == oneBtn) {
	result.setText(result.getText() + "1");
	} else if (eventSourceBtn == twoBtn) {
	result.setText(result.getText() + "2");
	} else if (eventSourceBtn == threeBtn) {
	result.setText(result.getText() + "3");
	} else if (eventSourceBtn == fourBtn) {
	result.setText(result.getText() + "4");
	} else if (eventSourceBtn == fiveBtn) {
	result.setText(result.getText() + "5");
	} else if (eventSourceBtn == sixBtn) {
	result.setText(result.getText() + "6");
	} else if (eventSourceBtn == sevenBtn) {
	result.setText(result.getText() + "7");
	} else if (eventSourceBtn == eightBtn) {
	result.setText(result.getText() + "8");
	} else if (eventSourceBtn == nineBtn) {
	result.setText(result.getText() + "9");
	} else if (eventSourceBtn == equalBtn) {
	operand2 = Integer.parseInt(result.getText());
	switch (operator) {
	case PLUS:
	resultNum = operand1 + operand2;
	break;
	case MINUS:
	resultNum = operand1 - operand2;
	break;
	case TIMES:
	resultNum = operand1 * operand2;
	break;
	case DIVIDE:
	resultNum = operand1 / operand2;
	break;
	}
	result.setText(resultNum + "");
	}
	}
	}

view raw Calculator.java hosted with ❤ by GitHub

There you go, we have just built a functional, GUI-based calculator application using Java AWT and Swing.