"Calculator"

src/Test.java

+import java.awt.*;
+import java.awt.event.ActionEvent;
+import java.awt.event.ActionListener;
+import java.awt.event.WindowEvent;
+import java.awt.event.WindowListener;
+
+public class Test implements WindowListener, ActionListener {
+    double num1, num2, ans;
+    String operand1, operand2, operator;
+    String numStr, ansStr;
+    TextField t;
+    Frame f;
+    Panel p;
+    Panel p2;
+    Button b1, b2, b3, b4, b5, b6, b7, b8, b9, b0, bPlus, bSub, bMul, bDiv, bEqual, bDot;
+
+    public Test() {
+        numStr = "";
+        f = new Frame("Easy Calculator");
+        f.setSize(400, 500);
+        f.setBackground(Color.gray);
+        f.addWindowListener(this);
+
+        p = new Panel();
+        p.setSize(200, 100);
+        p.setBackground(Color.pink);
+
+        t = new TextField();
+        t.setSize(400, 100);
+        t.setColumns(50);
+
+        p.add(t);
+
+        p2 = new Panel();
+        p2.setSize(100, 100);
+        p2.setBackground(Color.orange);
+
+        p2.setLayout(new GridLayout(4, 4));
+        b1 = new Button("1");
+        b2 = new Button("2");
+        b3 = new Button("3");
+        b4 = new Button("4");
+        b5 = new Button("5");
+        b6 = new Button("6");
+        b7 = new Button("7");
+        b8 = new Button("8");
+        b9 = new Button("9");
+        b0 = new Button("0");
+        bPlus = new Button("+");
+        bSub = new Button("-");
+        bMul = new Button("*");
+        bDiv = new Button("/");
+        bDot = new Button(".");
+        bEqual = new Button("=");
+
+        // Add listeners to buttons
+        b1.addActionListener(this);
+        b2.addActionListener(this);
+        b3.addActionListener(this);
+        b4.addActionListener(this);
+        b5.addActionListener(this);
+        b6.addActionListener(this);
+        b7.addActionListener(this);
+        b8.addActionListener(this);
+        b9.addActionListener(this);
+        b0.addActionListener(this);
+        bDot.addActionListener(this);
+        bPlus.addActionListener(this);
+        bSub.addActionListener(this);
+        bMul.addActionListener(this);
+        bDiv.addActionListener(this);
+        bEqual.addActionListener(this);
+
+        // Add buttons to panel
+        p2.add(b7);
+        p2.add(b8);
+        p2.add(b9);
+        p2.add(bPlus);
+        p2.add(b4);
+        p2.add(b5);
+        p2.add(b6);
+        p2.add(bSub);
+        p2.add(b1);
+        p2.add(b2);
+        p2.add(b3);
+        p2.add(bMul);
+        p2.add(b0);
+        p2.add(bDot);
+        p2.add(bEqual);
+        p2.add(bDiv);
+
+        f.add(p, BorderLayout.NORTH);
+        f.add(p2, BorderLayout.CENTER);
+        f.setVisible(true);
+    }
+
+    public static void main(String[] args) {
+        Test test2 = new Test();
+    }
+
+    @Override
+    public void windowActivated(WindowEvent arg0) { }
+
+    @Override
+    public void windowClosed(WindowEvent e) { }
+
+    @Override
+    public void windowClosing(WindowEvent e) {
+        System.exit(0);
+    }
+
+    @Override
+    public void windowDeactivated(WindowEvent e) { }
+
+    @Override
+    public void windowDeiconified(WindowEvent e) { }
+
+    @Override
+    public void windowIconified(WindowEvent e) { }
+
+    @Override
+    public void windowOpened(WindowEvent e) { }
+
+    @Override
+    public void actionPerformed(ActionEvent e) {
+        String cmd = e.getActionCommand();
+
+        // If a number or decimal is pressed
+        if (cmd.equals("0") || cmd.equals("1") || cmd.equals("2") || cmd.equals("3") ||
+                cmd.equals("4") || cmd.equals("5") || cmd.equals("6") || cmd.equals("7") ||
+                cmd.equals("8") || cmd.equals("9") || cmd.equals(".")) {
+            numStr = numStr + cmd;
+            t.setText(numStr);
+        }
+        // If an operator is pressed
+        else if (cmd.equals("+") || cmd.equals("-") || cmd.equals("*") || cmd.equals("/")) {
+            operand1 = numStr;
+            operator = cmd;
+            numStr = "";
+        }
+        // If equal sign is pressed
+        else if (cmd.equals("=")) {
+            operand2 = numStr;
+            num1 = Double.parseDouble(operand1);
+            num2 = Double.parseDouble(operand2);
+            switch (operator) {
+                case "+":
+                    ans = num1 + num2;
+                    break;
+                case "-":
+                    ans = num1 - num2;
+                    break;
+                case "*":
+                    ans = num1 * num2;
+                    break;
+                case "/":
+                    if (num2 != 0) {
+                        ans = num1 / num2;
+                    } else {
+                        ansStr = "Error";
+                        t.setText(ansStr);
+                        return;
+                    }
+                    break;
+            }
+            ansStr = Double.toString(ans);
+            t.setText(ansStr);
+        }
+    }
+}
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