Added support for decimal numbers

src/calculator/Calc.java

@@ -6,27 +6,31 @@ import java.util.regex.Pattern;
 
 public class Calc {
 
-	private static final Pattern MULTIPLY = Pattern.compile("([0-9]+)\\*([0-9]+)");
+	private static final Pattern MULTIPLY = Pattern.compile("([0-9\\.]+)\\*([0-9\\.]+)");
-	private static final Pattern DIVIDE = Pattern.compile("([0-9]+)\\/([0-9]+)");
+	private static final Pattern DIVIDE = Pattern.compile("([0-9\\.]+)\\/([0-9\\.]+)");
-	private static final Pattern ADD = Pattern.compile("([0-9]+)\\+([0-9]+)");
+	private static final Pattern ADD = Pattern.compile("([0-9\\.]+)\\+([0-9\\.]+)");
-	private static final Pattern SUBTRACT = Pattern.compile("([0-9]+)\\-([0-9]+)");
+	private static final Pattern SUBTRACT = Pattern.compile("([0-9\\.]+)\\-([0-9\\.]+)");
 
-	public static int calculate(String text) {
+	public static Double calculate(String text) {
 		StringBuffer buf = new StringBuffer(text);
 		replace(buf, MULTIPLY, (a, b) -> a * b);
 		replace(buf, DIVIDE, (a, b) -> a / b);
 		replace(buf, ADD, (a, b) -> a + b);
 		replace(buf, SUBTRACT, (a, b) -> a - b);
-		return Integer.parseInt(buf.toString());
+		try {
+			return Double.parseDouble(buf.toString());
+		} catch (Exception e) {
+			return null;
+		}
 	}
 
-	private static void replace(StringBuffer buf, Pattern pattern, BiFunction<Integer, Integer, Integer> doit) {
+	private static void replace(StringBuffer buf, Pattern pattern, BiFunction<Double, Double, Double> doit) {
 		while (true) {
 			Matcher matcher = pattern.matcher(buf.toString());
 			if (!matcher.find())
 				break;
-			buf.replace(matcher.start(), matcher.end(), Integer
+			buf.replace(matcher.start(), matcher.end(), Double
-					.toString(doit.apply(Integer.parseInt(matcher.group(1)), Integer.parseInt(matcher.group(2)))));
+					.toString(doit.apply(Double.parseDouble(matcher.group(1)), Double.parseDouble(matcher.group(2)))));
 		}
 	}
 }

src/calculator/Gui.java

@@ -5,9 +5,13 @@ import java.awt.Dimension;
 import java.awt.GridLayout;
 import java.awt.event.ActionEvent;
 import java.awt.event.ActionListener;
+import java.awt.event.KeyEvent;
+import java.awt.event.KeyListener;
 
 import javax.swing.JButton;
+import javax.swing.JDialog;
 import javax.swing.JFrame;
+import javax.swing.JOptionPane;
 import javax.swing.JPanel;
 import javax.swing.JTextField;
 import javax.swing.UIManager;
@@ -20,27 +24,58 @@ public class Gui {
 
 	public Gui() throws Exception {
 		frame = new JFrame();
-		frame.setMinimumSize(new Dimension(200, 400));
+		frame.setMinimumSize(new Dimension(300, 400));
 		frame.setTitle("Calculator");
 		frame.setLayout(new BorderLayout(10, 10));
 		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
+		frame.addKeyListener(new KeyListener() {
+
+			@Override
+			public void keyTyped(KeyEvent e) {
+				if (e.getKeyChar() == '+')
+					tf.setText(tf.getText() + '+');
+				else if (e.getKeyChar() == '-')
+					tf.setText(tf.getText() + "-");
+				else if (e.getKeyChar() == '*')
+					tf.setText(tf.getText() + "*");
+				else if (e.getKeyChar() == '/')
+					tf.setText(tf.getText() + "/");
+				else if (e.getKeyChar() == '.')
+					tf.setText(tf.getText() + ".");
+				else if (e.getKeyChar() == '\n') {
+					calc();
+				} else if (e.getKeyChar() == '\b' && tf.getText().length() > 0)
+					tf.setText(tf.getText().substring(0, tf.getText().length() - 1));
+				else if (e.getKeyChar() >= '0' && e.getKeyChar() <= '9')
+					tf.setText(tf.getText() + e.getKeyChar());
+			}
+
+			@Override
+			public void keyReleased(KeyEvent e) {
+			}
+
+			@Override
+			public void keyPressed(KeyEvent e) {
+			}
+		});
 		UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
 		tf = new JTextField();
 		tf.setFocusable(false);
 		frame.add(tf, BorderLayout.NORTH);
 		panel = new JPanel();
 		frame.add(panel, BorderLayout.CENTER);
-		panel.setLayout(new GridLayout(5, 3));
+		panel.setLayout(new GridLayout(4, 4));
-		String str = addNumbers();
+		String str = addNumbers("+-*");
-		str += "+0-*/";
+		str += ".0";
 		addAppendButtons(str);
 		addButton('=').addActionListener(new ActionListener() {
 
 			@Override
 			public void actionPerformed(ActionEvent e) {
-				tf.setText(Integer.toString(Calc.calculate(tf.getText())));
+				calc();
 			}
 		});
+		addAppendButtons("/");
 	}
 
 	public void show() {
@@ -51,10 +86,13 @@ public class Gui {
 		frame.dispose();
 	}
 
-	private String addNumbers() {
+	private String addNumbers(String rowend) {
 		String str = "";
+		int x = 0;
 		for (int i = 1; i < 10; i++) {
 			str += i;
+			if (i % 3 == 0)
+				str += rowend.charAt(x++);
 		}
 		return str;
 	}
@@ -81,4 +119,24 @@ public class Gui {
 		panel.add(num);
 		return num;
 	}
+
+	private void calc() {
+		try {
+			Double ret = Calc.calculate(tf.getText());
+			if (ret == null)
+				JOptionPane.showMessageDialog(frame, "Unable to convert result to number!", "Error!",
+						JOptionPane.WARNING_MESSAGE);
+			else
+				tf.setText(Double.toString(ret));
+		} catch (ArithmeticException e) {
+			JOptionPane.showMessageDialog(frame, "Arithmetic error: " + e.getMessage(), "Error!",
+					JOptionPane.WARNING_MESSAGE);
+		} catch (NumberFormatException e) {
+			JOptionPane.showMessageDialog(frame,
+					"Number format error: " + e.getMessage() + "\n\nThe number may be too large.", "Error!",
+					JOptionPane.WARNING_MESSAGE);
+		} catch (Exception e) {
+			JOptionPane.showMessageDialog(frame, "Unknown error!\n" + e, "Error!", JOptionPane.WARNING_MESSAGE);
+		}
+	}
 }