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I know there's loads of these out there but I thought I'd give it a shot. My mate made a calculator but he used a GUI Builder and I personally prefer typing my GUI's by hand.

I've finished my first year of university (moving on to my second year) and I'm studying BSc Artificial Intelligence and Robotics, I wanted to test my Java skills considering I finished like a month ago and wanted to see what I could remember.

I'm uploading the code here, for any advice as I'd like to type Java with the correct rules, regulations and 'good habits'.

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;
import javax.swing.JFrame;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Image;
import javax.swing.ImageIcon;
public class Main extends JFrame
{
 private Interface anInterface = new Interface();
 private ImagePanel imagePanel = new ImagePanel();
 private String request = "";
 public Main()
 {
 imagePanel.add(anInterface);
 add(imagePanel);
 actions();
 pack();
 setVisible(true);
 setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 setLocationRelativeTo(null);
 setSize(225, 300);
 setTitle("Calculator");
 setResizable(false);
 }
 public void actions()
 {
 anInterface.calculatorButtons.zero.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 String text = anInterface.calculatorScreen.results.getText();
 request += 0;
 anInterface.calculatorScreen.results.setText(text + 0);
 }
 });
 anInterface.calculatorButtons.one.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 String text = anInterface.calculatorScreen.results.getText();
 request += 1;
 anInterface.calculatorScreen.results.setText(text + 1);
 }
 });
 anInterface.calculatorButtons.two.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 String text = anInterface.calculatorScreen.results.getText();
 request += 2;
 anInterface.calculatorScreen.results.setText(text + 2);
 }
 });
 anInterface.calculatorButtons.three.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 String text = anInterface.calculatorScreen.results.getText();
 request += 3;
 anInterface.calculatorScreen.results.setText(text + 3);
 }
 });
 anInterface.calculatorButtons.four.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 String text = anInterface.calculatorScreen.results.getText();
 request += 4;
 anInterface.calculatorScreen.results.setText(text + 4);
 }
 });
 anInterface.calculatorButtons.five.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 String text = anInterface.calculatorScreen.results.getText();
 request += 5;
 anInterface.calculatorScreen.results.setText(text + 5);
 }
 });
 anInterface.calculatorButtons.six.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 String text = anInterface.calculatorScreen.results.getText();
 request += 6;
 anInterface.calculatorScreen.results.setText(text + 6);
 }
 });
 anInterface.calculatorButtons.seven.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 String text = anInterface.calculatorScreen.results.getText();
 request += 7;
 anInterface.calculatorScreen.results.setText(text + 7);
 }
 });
 anInterface.calculatorButtons.eight.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 String text = anInterface.calculatorScreen.results.getText();
 request += 8;
 anInterface.calculatorScreen.results.setText(text + 8);
 }
 });
 anInterface.calculatorButtons.nine.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 String text = anInterface.calculatorScreen.results.getText();
 request += 9;
 anInterface.calculatorScreen.results.setText(text + 9);
 }
 });
 anInterface.calculatorButtons.dot.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 String text = anInterface.calculatorScreen.results.getText();
 request += ".";
 anInterface.calculatorScreen.results.setText(text + ".");
 }
 });
 anInterface.calculatorButtons.plus.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 String text = anInterface.calculatorScreen.results.getText();
 request += "+";
 anInterface.calculatorScreen.results.setText(text + "+");
 }
 });
 anInterface.calculatorButtons.divide.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 String text = anInterface.calculatorScreen.results.getText();
 request += "/";
 anInterface.calculatorScreen.results.setText(text + "÷");
 }
 });
 anInterface.calculatorButtons.multiply.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 String text = anInterface.calculatorScreen.results.getText();
 request += "*";
 anInterface.calculatorScreen.results.setText(text + ×ばつ");
 }
 });
 anInterface.calculatorButtons.minus.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 String text = anInterface.calculatorScreen.results.getText();
 request += "-";
 anInterface.calculatorScreen.results.setText(text + "-");
 }
 });
 anInterface.calculatorButtons.ac.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 request = "";
 anInterface.calculatorScreen.results.setText("");
 }
 });
 anInterface.clearButton.equals.addActionListener(new ActionListener()
 {
 @Override
 public void actionPerformed(ActionEvent e)
 {
 try
 {
 ScriptEngineManager mgr = new ScriptEngineManager();
 ScriptEngine engine = mgr.getEngineByName("JavaScript");
 String answer = engine.eval(request).toString();
 anInterface.calculatorScreen.results.setText("" + answer);
 request = answer;
 }
 catch(ScriptException | NullPointerException e1)
 {
 anInterface.calculatorScreen.results.setText("ERROR");
 }
 }
 });
 }
 public static void main(String[] args)
 {
 Main itf = new Main();
 }
}
class CalculatorButtons extends JPanel
{
 protected JButton zero;
 protected JButton one;
 protected JButton two;
 protected JButton three;
 protected JButton four;
 protected JButton five;
 protected JButton six;
 protected JButton seven;
 protected JButton eight;
 protected JButton nine;
 protected JButton dot;
 protected JButton plus;
 protected JButton divide;
 protected JButton multiply;
 protected JButton minus;
 protected JButton ac;
 public CalculatorButtons()
 {
 setOpaque(false);
 setLayout(new GridBagLayout());
 zero = new JButton("0");
 one = new JButton("1");
 two = new JButton("2");
 three = new JButton("3");
 four = new JButton("4");
 five = new JButton("5");
 six = new JButton("6");
 seven = new JButton("7");
 eight = new JButton("8");
 nine = new JButton("9");
 dot = new JButton(".");
 plus = new JButton("+");
 divide = new JButton("÷");
 multiply = new JButton(×ばつ");
 minus = new JButton("-");
 ac = new JButton("AC");
 JLabel space = new JLabel(" ");
 GridBagConstraints gbc = new GridBagConstraints();
 gbc.ipadx = -20;
 gbc.gridx = 0;
 gbc.gridy = 4;
 gbc.anchor = GridBagConstraints.WEST;
 add(zero, gbc);
 gbc.anchor = GridBagConstraints.CENTER;
 add(dot, gbc);
 gbc.anchor = GridBagConstraints.EAST;
 add(ac, gbc);
 gbc.gridx = 0;
 gbc.gridy = 3;
 gbc.anchor = GridBagConstraints.WEST;
 add(one, gbc);
 gbc.anchor = GridBagConstraints.CENTER;
 add(two, gbc);
 gbc.anchor = GridBagConstraints.EAST;
 add(three, gbc);
 gbc.gridx = 0;
 gbc.gridy = 2;
 gbc.anchor = GridBagConstraints.WEST;
 add(four, gbc);
 gbc.anchor = GridBagConstraints.CENTER;
 add(five, gbc);
 gbc.anchor = GridBagConstraints.EAST;
 add(six, gbc);
 gbc.gridx = 0;
 gbc.gridy = 1;
 gbc.anchor = GridBagConstraints.WEST;
 add(seven, gbc);
 gbc.anchor = GridBagConstraints.CENTER;
 add(eight, gbc);
 gbc.anchor = GridBagConstraints.EAST;
 add(nine, gbc);
 gbc.gridx = 1;
 gbc.gridy = 1;
 add(plus, gbc);
 gbc.gridx = 1;
 gbc.gridy = 2;
 add(divide, gbc);
 gbc.gridx = 1;
 gbc.gridy = 3;
 add(multiply, gbc);
 gbc.gridx = 1;
 gbc.gridy = 4;
 add(minus, gbc);
 gbc.gridx = 0;
 gbc.gridy = 5;
 add(space);
 }
}
class CalculatorScreen extends JPanel
{
 protected JTextArea results;
 protected JScrollPane scrollPane;
 public CalculatorScreen()
 {
 setOpaque(false);
 results = new JTextArea(5, 16);
 results.setEditable(false);
 results.setLineWrap(true);
 scrollPane = new JScrollPane(results);
 GridBagConstraints gbc = new GridBagConstraints();
 gbc.gridx = 0;
 gbc.gridy = 0;
 add(scrollPane, gbc);
 }
}
class ClearButton extends JPanel
{
 protected JButton equals;
 public ClearButton()
 {
 setOpaque(false);
 setLayout(new GridBagLayout());
 equals = new JButton("=");
 GridBagConstraints gbc = new GridBagConstraints();
 gbc.gridx = 0;
 gbc.gridy = 0;
 gbc.ipadx = 124;
 add(equals, gbc);
 }
}
class ImagePanel extends JPanel
{
 protected Image loginImage;
 public ImagePanel()
 {
 this.loginImage =
 new ImageIcon(getClass().getResource("Pics/CalcBackground.jpg")).getImage();
 Dimension size = new Dimension(loginImage.getWidth(null), loginImage.getHeight(null));
 setPreferredSize(size);
 setMinimumSize(size);
 setMaximumSize(size);
 setSize(size);
 setLayout(new GridBagLayout());
 }
 protected void paintComponent(Graphics g) {
 g.drawImage(loginImage, 0, 0, null);
 }
}
class Interface extends JPanel
{
 protected CalculatorScreen calculatorScreen = new CalculatorScreen();
 protected CalculatorButtons calculatorButtons = new CalculatorButtons();
 protected ClearButton clearButton = new ClearButton();
 Interface()
 {
 setOpaque(false);
 setLayout(new GridBagLayout());
 GridBagConstraints gbc = new GridBagConstraints();
 gbc.gridx = 0;
 gbc.gridy = 0;
 add(calculatorScreen, gbc);
 gbc.ipady = 0;
 gbc.gridx = 0;
 gbc.gridy = 1;
 add(calculatorButtons, gbc);
 gbc.gridx = 0;
 gbc.gridy = 2;
 add(clearButton, gbc);
 }
}

Image of the Calculator

The link for the background image of the calculator: http://imgur.com/zZehZlX

So, I'm not sure if I'm a beginner? I class my self as a beginner as I have no idea what level of skill you stop being a beginner at. The code itself is in 6 different separate classes, I've been told previously on StackOverflow to submit my code in one file, so that's what I've done here.

I realise that I have a lot of actions for buttons when I could try to limit those and make it more reusable just not sure how.

Any help on improving my style of typing code would be helpful, and I appreciate every bit.

Thanks.