Added files

src/calculator/Calc.java

@@ -0,0 +1,32 @@
+package calculator;
+
+import java.util.function.BiFunction;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class Calc {
+
+	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 ADD = Pattern.compile("([0-9]+)\\+([0-9]+)");
+	private static final Pattern SUBTRACT = Pattern.compile("([0-9]+)\\-([0-9]+)");
+
+	public static int 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());
+	}
+
+	private static void replace(StringBuffer buf, Pattern pattern, BiFunction<Integer, Integer, Integer> doit) {
+		while (true) {
+			Matcher matcher = pattern.matcher(buf.toString());
+			if (!matcher.find())
+				break;
+			buf.replace(matcher.start(), matcher.end(), Integer
+					.toString(doit.apply(Integer.parseInt(matcher.group(1)), Integer.parseInt(matcher.group(2)))));
+		}
+	}
+}

src/calculator/Gui.java

@@ -0,0 +1,84 @@
+package calculator;
+
+import java.awt.BorderLayout;
+import java.awt.Dimension;
+import java.awt.GridLayout;
+import java.awt.event.ActionEvent;
+import java.awt.event.ActionListener;
+
+import javax.swing.JButton;
+import javax.swing.JFrame;
+import javax.swing.JPanel;
+import javax.swing.JTextField;
+import javax.swing.UIManager;
+import javax.swing.UnsupportedLookAndFeelException;
+
+public class Gui {
+	private JFrame frame;
+	private JPanel panel;
+	private JTextField tf;
+
+	public Gui() throws Exception {
+		frame = new JFrame();
+		frame.setMinimumSize(new Dimension(200, 400));
+		frame.setTitle("Calculator");
+		frame.setLayout(new BorderLayout(10, 10));
+		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
+		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));
+		String str = addNumbers();
+		str += "+0-*/";
+		addAppendButtons(str);
+		addButton('=').addActionListener(new ActionListener() {
+
+			@Override
+			public void actionPerformed(ActionEvent e) {
+				tf.setText(Integer.toString(Calc.calculate(tf.getText())));
+			}
+		});
+	}
+
+	public void show() {
+		frame.setVisible(true);
+	}
+
+	public void close() {
+		frame.dispose();
+	}
+
+	private String addNumbers() {
+		String str = "";
+		for (int i = 1; i < 10; i++) {
+			str += i;
+		}
+		return str;
+	}
+
+	private void addAppendButtons(String btns) {
+		for (int i = 0; i < btns.length(); i++) {
+			Character c = btns.charAt(i);
+			JButton num = addButton(c);
+			final Character number = c;
+			num.addActionListener(new ActionListener() {
+
+				@Override
+				public void actionPerformed(ActionEvent e) {
+					tf.setText(tf.getText() + number);
+				}
+			});
+		}
+	}
+
+	private JButton addButton(Character c) {
+		JButton num = new JButton();
+		num.setText(Character.toString(c));
+		num.setFocusable(false);
+		panel.add(num);
+		return num;
+	}
+}

src/calculator/Main.java

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+package calculator;
+
+public class Main {
+	public static void main(String[] args) throws Exception {
+		Gui gui = new Gui();
+		gui.show();
+	}
+}