A very basic Java calculator that calculates only single digit numbers

Question

How should I incorporate a JButton array, and how do I get rid of the multitude of action listeners? I would also like to modify it so that you can do more than one operation on numbers with multiple digits.

/*
 * A one operation calculator.
 * Only handles single digits for basic arithmetic.
 * Trig operations accept values in degrees.
 * 
 * I'll make a real calculator later.
 */
public class BasicCalculator extends JFrame {
 private JPanel panel; 
 private JTextField input; 
 private JButton butt0, butt1, butt2, butt3,
 butt4, butt5, butt6, butt7,
 butt8, butt9, buttSine, buttCosine,
 buttEquals, buttClear, buttAdd,
 buttSubtract, buttMultiply, buttDivide,
 buttTangent;
 private final int WINDOW_WIDTH = 360; 
 private final int WINDOW_HEIGHT = 300;
/*
 * Constructor calls the superclass's constructor and creates the window.
 */
 public BasicCalculator() {
 super("Calculate a Simple Expression");
 setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
 setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 buildPanel();
 add(panel);
 setVisible(true);
 }
/*
 * Method to put the input box and all the buttons onto the window.
 * 
 * I know, I know, I should've used an array for the buttons.
 */
 private void buildPanel() {
 input = new JTextField(16);
 buttEquals = new JButton("=");
 buttEquals.addActionListener(new Listener1());
 buttClear = new JButton("AC");
 buttClear.addActionListener(new Listener2());
 buttAdd = new JButton("+");
 buttAdd.addActionListener(new Listener3());
 buttSubtract = new JButton("-");
 buttSubtract.addActionListener(new Listener4());
 buttMultiply = new JButton("x");
 buttMultiply.addActionListener(new Listener5());
 buttDivide = new JButton("÷");
 buttDivide.addActionListener(new Listener6());
 butt0 = new JButton("0");
 butt0.addActionListener(new Listener7());
 butt1 = new JButton("1");
 butt1.addActionListener(new Listener8());
 butt2 = new JButton("2");
 butt2.addActionListener(new Listener9());
 butt3 = new JButton("3");
 butt3.addActionListener(new Listener10());
 butt4 = new JButton("4");
 butt4.addActionListener(new Listener11());
 butt5 = new JButton("5");
 butt5.addActionListener(new Listener12());
 butt6 = new JButton("6");
 butt6.addActionListener(new Listener13());
 butt7 = new JButton("7");
 butt7.addActionListener(new Listener14());
 butt8 = new JButton("8");
 butt8.addActionListener(new Listener15());
 butt9 = new JButton("9");
 butt9.addActionListener(new Listener16());
 buttSine = new JButton("sin");
 buttSine.addActionListener(new Listener17());
 buttCosine = new JButton("cos");
 buttCosine.addActionListener(new Listener18());
 buttTangent = new JButton("tan");
 buttTangent.addActionListener(new Listener19());
 panel = new JPanel();
 panel.setLayout(new FlowLayout(FlowLayout.CENTER, 10, 30));
 panel.add(input);
 panel.add(buttEquals);
 panel.add(buttClear);
 panel.add(buttAdd);
 panel.add(buttSubtract);
 panel.add(buttMultiply);
 panel.add(buttDivide);
 panel.add(butt0);
 panel.add(butt1);
 panel.add(butt2);
 panel.add(butt3);
 panel.add(butt4);
 panel.add(butt5);
 panel.add(butt6);
 panel.add(butt7);
 panel.add(butt8);
 panel.add(butt9);
 panel.add(buttSine);
 panel.add(buttCosine);
 panel.add(buttTangent);
 }
/*
 * Action listener for the "equals" button.
 * All the calculations are done here.
 */
 private class Listener1 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 String str = input.getText();
 double num1, num2, radians, result;
 if (str.charAt(0) == 's' || str.charAt(0) == 'c' || str.charAt(0) == 't') 
 {
 radians = Math.toRadians(Double.parseDouble(str.substring(3)));
 switch (str.charAt(0)) {
 case 's':
 result = Math.sin(radians);
 break;
 case 'c':
 result = Math.cos(radians);
 break;
 case 't':
 result = Math.tan(radians);
 break;
 default:
 result = 0; 
 }
 } 
 else 
 {
 num1 = Double.parseDouble(str.substring(0, 1));
 num2 = Double.parseDouble(str.substring(4, 5));
 switch (str.charAt(2)) {
 case '+':
 result = num1 + num2;
 break;
 case '-':
 result = num1 - num2;
 break;
 case 'x':
 result = num1 * num2;
 break;
 case '÷':
 result = num1 / num2;
 break;
 default:
 result = 0;
 }
 }
 input.setText(Double.toString(result)); 
 JOptionPane.showMessageDialog(null, str + " = " + result);
 }
 }
/*
 * The rest of the action listeners print the button text to the text field.
 */
 private class Listener2 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText("");
 }
 }
 private class Listener3 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + " + ");
 }
 }
 private class Listener4 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + " - ");
 }
 }
 private class Listener5 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + " x ");
 }
 }
 private class Listener6 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + " ÷ ");
 }
 }
 private class Listener7 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + "0");
 }
 }
 private class Listener8 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + "1");
 }
 }
 private class Listener9 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + "2");
 }
 }
 private class Listener10 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + "3");
 }
 } 
 private class Listener11 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + "4");
 }
 }
 private class Listener12 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + "5");
 }
 }
 private class Listener13 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + "6");
 }
 }
 private class Listener14 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + "7");
 }
 }
 private class Listener15 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + "8");
 }
 }
 private class Listener16 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + "9");
 }
 }
 private class Listener17 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + "sin");
 }
 }
 private class Listener18 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + "cos");
 }
 }
 private class Listener19 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + "tan");
 }
 }
/*
 * main method
 */
 public static void main(String[] args) {
 new BasicCalculator();
 }
}

Answer 1

You don't need to have implementations consisting of just single line. For example, you can replace the Listener2 direclty with a lambda as :

buttClear = new JButton("AC");
buttClear.addActionListener(event -> input.setText(""));

Same goes will all one liner Listeners in your code.

There's also a bug in your code because of the way you are extracting numbers from the input field.
If you perform 4/3, you will get the result as 1.3333333, and if you continue doing more operations like 1.333333*3, your calculator returns the result as 0.0.

Answer 2

This is the power of classes: they encapsulate a common concept, so that you write them once, and reuse them multiple times. (And all in all this is the main act of programming: spot common patterns and derieve generalizations from these patterns.)

So, you have multiple classes along the lines of:

private class Listener17 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + "sin");
 }
}
private class Listener18 implements ActionListener {
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + "cos");
 }
} 

... which differ only in the text you append. Thus, make ONE class of these, and pass the text to append as a parameter:

private class AppendingTextListener implements ActionListener {
 private final String textToAppend;
 AppendingTextListener(String textToAppend) {
 this.textToAppend = textToAppend;
 }
 public void actionPerformed(ActionEvent e) {
 input.setText(input.getText() + textToAppend);
 }
}

and then:

butt0.addActionListener(new AppendingTextListener("0"));
butt1.addActionListener(new AppendingTextListener("1"));
...