I've made an IDE in Java, using swing. It uses a couple of resources (prefs.json and help.txt) and some imported jar files for reading the json. I know the code's quite long, but the answer doesn't have to be a very detailed one. Anyway, here's the code:

package io.j4cobgarby.github;

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Paths;

import javax.swing.AbstractAction;
import javax.swing.Box;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JPopupMenu;
import javax.swing.JScrollBar;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.JToolBar;
import javax.swing.SwingConstants;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.CaretEvent;
import javax.swing.event.CaretListener;

import org.json.JSONException;
import org.json.JSONObject;

public class Main {

    private JFrame frame;
    private JTextField textField;

    public static String currentFile = null;
    private static java.util.Scanner scanner;
    private JTextField cmd2Run;

    JSONObject prefs = null;

    String osType = "Unknown";

    static JTextArea area = new JTextArea();

    static JLabel filenameLabel = new JLabel("");
    private JTextField status;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    Main window = new Main();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     * 
     * @throws IOException
     * @throws JSONException
     */
    public Main() throws IOException, JSONException {
        initialize();

        String prefsText = convertStreamToString(Main.class.getResourceAsStream("prefs.json"));

        osType = (System.getProperty("os.name").startsWith("Windows") ? "win" : "unix");
        System.out.println(osType);

        try {
            prefs = new JSONObject(prefsText);
        } catch (JSONException e) {
            e.printStackTrace();
        }

        String pyCommandWin = (String) prefs.get("pyCommandWin");
        String pyCommandUnix = (String) prefs.get("pyCommandUnix");
        String lastFile = (String) prefs.get("lastFile");
        int tabSize = prefs.getInt("tabSize");
        area.setTabSize(tabSize);

        area.addCaretListener(new CaretListener() {
            public void caretUpdate(CaretEvent e) {
                JTextArea editArea = (JTextArea) e.getSource();

                int linenum = 1;
                int columnnum = 1;

                try {
                    int caretpos = editArea.getCaretPosition();
                    linenum = editArea.getLineOfOffset(caretpos);

                    columnnum = caretpos - editArea.getLineStartOffset(linenum);

                    linenum += 1;
                } catch (Exception ex) {
                }

                updateStatus(linenum, columnnum);
            }
        });

        frame.getContentPane().add(area, BorderLayout.CENTER);

        status = new JTextField();
        frame.getContentPane().add(status, BorderLayout.SOUTH);

        updateStatus(1, 1);

        System.out.println(System.getProperty("os.name") + " is " + osType);

        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (ClassNotFoundException e2) {
            e2.printStackTrace();
        } catch (InstantiationException e2) {
            e2.printStackTrace();
        } catch (IllegalAccessException e2) {
            e2.printStackTrace();
        } catch (UnsupportedLookAndFeelException e2) {
            e2.printStackTrace();
        }
        frame.setTitle("Python IDE");
        JToolBar toolBar = new JToolBar();
        toolBar.setFloatable(false);
        frame.getContentPane().add(toolBar, BorderLayout.NORTH);

        Component horizontalStrut_2 = Box.createHorizontalStrut(20);
        toolBar.add(horizontalStrut_2);

        area.setFont(new Font("Courier New", Font.PLAIN, 12));
        // area.setText(convertStreamToString(Main.class.getResourceAsStream("help.txt")));
        area.setText((lastFile.isEmpty()) ? convertStreamToString(Main.class.getResourceAsStream("help.txt"))
                : readFile(lastFile, Charset.defaultCharset()));
        frame.getContentPane().add(area, BorderLayout.CENTER);

        filenameLabel.setFont(new Font("Tahoma", Font.PLAIN, 11));
        filenameLabel.setToolTipText("File name");
        toolBar.add(filenameLabel);
        filenameLabel.setText("Untitled");

        Component horizontalStrut_6 = Box.createHorizontalStrut(20);
        toolBar.add(horizontalStrut_6);

        JButton btnRun = new JButton("Run in python");
        btnRun.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                // cmd2Run.setText(pyCommandWin + " " + currentFile);
                runPython((osType == "win") ? pyCommandWin : pyCommandUnix);
            }
        });
        toolBar.add(btnRun);

        Component horizontalStrut_1 = Box.createHorizontalStrut(20);
        toolBar.add(horizontalStrut_1);

        Component horizontalStrut_7 = Box.createHorizontalStrut(2);
        toolBar.add(horizontalStrut_7);

        JButton btnRunThisCommand = new JButton("Run this command");
        btnRunThisCommand
                .setToolTipText("Use this for running a script in a different language, or for command line args.");
        btnRunThisCommand.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                // format command so that text within braces is checked

                Runtime rt = Runtime.getRuntime();
                try {
                    rt.exec("cmd.exe /c start cmd.exe /k \"" + cmd2Run.getText() + "\"");
                } catch (IOException e1) {
                    e1.printStackTrace();
                }
            }
        });
        toolBar.add(btnRunThisCommand);

        cmd2Run = new JTextField();
        cmd2Run.setToolTipText("Use this for running a script in a different language, or for command line args.");
        cmd2Run.setHorizontalAlignment(SwingConstants.LEFT);
        cmd2Run.setFont(new Font("Courier New", Font.PLAIN, 11));
        toolBar.add(cmd2Run);
        cmd2Run.setColumns(5);

        Component horizontalStrut = Box.createHorizontalStrut(300);
        toolBar.add(horizontalStrut);

        textField = new JTextField();
        textField.setHorizontalAlignment(SwingConstants.RIGHT);
        textField.setText(new File(System.getProperty("user.home")).toString());
        toolBar.add(textField);
        textField.setColumns(10);

        JButton btnLoadFile = new JButton("Load file");
        btnLoadFile.setHorizontalAlignment(SwingConstants.RIGHT);
        btnLoadFile.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                loadFile(textField.getText());
            }

        });
        toolBar.add(btnLoadFile);

        JToolBar toolBar_1 = new JToolBar();
        toolBar_1.setFloatable(false);
        frame.getContentPane().add(toolBar_1, BorderLayout.SOUTH);

        status = new JTextField();
        status.setEditable(false);
        toolBar_1.add(status);
        status.setColumns(10);

        JButton btnSettings = new JButton("Settings");
        btnSettings.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                File file = new File("src/io/j4cobgarby/github/prefs.json");
                loadFile(file.getAbsolutePath());
            }
        });
        toolBar_1.add(btnSettings);

        JScrollPane scrollPane = new JScrollPane(area);
        frame.getContentPane().add(scrollPane, BorderLayout.CENTER);

        JMenuBar menuBar = new JMenuBar();
        frame.setJMenuBar(menuBar);

        JMenu mnFile = new JMenu("File");
        menuBar.add(mnFile);

        JMenuItem mntmSaveCurrentFile = new JMenuItem(new AbstractAction("Save file") {
            public void actionPerformed(ActionEvent e) {
                saveFile(currentFile);
            }
        });
        mntmSaveCurrentFile.setText("Save current file");
        mnFile.add(mntmSaveCurrentFile);

        JMenuItem mntmSaveUnderDifferent = new JMenuItem(new AbstractAction("Save file as..") {
            public void actionPerformed(ActionEvent e) {
                JTextField saveFileName = new JTextField(System.getProperty("user.home"));
                JPanel panel = new JPanel(new GridLayout(0, 1));
                panel.add(new JLabel("What would you like to save this file as?"));
                panel.add(saveFileName);
                int result = JOptionPane.showConfirmDialog(null, panel, "Save as..", JOptionPane.OK_CANCEL_OPTION,
                        JOptionPane.PLAIN_MESSAGE);
                if (result == JOptionPane.OK_OPTION) {
                    // On OK
                    saveFile(saveFileName.getText());
                } else {
                    System.out.println("Cancelled");
                }
            }
        });
        mntmSaveUnderDifferent.setText("Save as..");
        mnFile.add(mntmSaveUnderDifferent);

        JMenuItem mntmCreateNewFile = new JMenuItem(new AbstractAction("Create new file") {
            public void actionPerformed(ActionEvent e) {
                JTextField newFilePath = new JTextField(System.getProperty("user.home"));
                JPanel panel = new JPanel(new GridLayout(0, 1));
                panel.add(new JLabel("Path for new file:"));
                panel.add(newFilePath);
                int result = JOptionPane.showConfirmDialog(null, panel, "New file", JOptionPane.OK_CANCEL_OPTION,
                        JOptionPane.PLAIN_MESSAGE);
                if (result == JOptionPane.OK_OPTION) {
                    // On OK
                    newFile(newFilePath.getText());
                } else {
                    System.out.println("Cancelled");
                }
            }
        });
        mnFile.add(mntmCreateNewFile);
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        frame = new JFrame();
        frame.setBounds(100, 100, 938, 618);
        frame.addWindowListener(new java.awt.event.WindowAdapter() {
            @Override
            public void windowClosing(java.awt.event.WindowEvent windowEvent) {
                if (JOptionPane.showConfirmDialog(frame, "Are you sure you wish to exit?", "Quit",
                        JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE) == JOptionPane.YES_OPTION) {
                    try {
                        System.out.println("Exiting");
                        System.out.println(prefs.toString(4));
                    } catch (JSONException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    System.exit(0);
                }
            }
        });
        frame.setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
    }

    /*
     * _    _      _                    __             _   _                   
     *| |  | |    | |                  / _|           | | (_)                _ 
     *| |__| | ___| |_ __   ___ _ __  | |_ _   _ _ __ | |_ _  ___  _ __  ___(_)
     *|  __  |/ _ \ | '_ \ / _ \ '__| |  _| | | | '_ \| __| |/ _ \| '_ \/ __|  
     *| |  | |  __/ | |_) |  __/ |    | | | |_| | | | | |_| | (_) | | | \__ \_ 
     *|_|  |_|\___|_| .__/ \___|_|    |_|  \__,_|_| |_|\__|_|\___/|_| |_|___(_)
     *              | |                                                        
     *              |_|                                                        
     */

    /*
     * Create a new file from a String path
     */
    private static void newFile(String path) {
        File file = new File(path);
        try {
            file.createNewFile();
            loadFile(path);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /*
     * Save a file to a String path
     */
    private static void saveFile(String saveTo) {
        FileWriter fwrite = null;
        try {
            fwrite = new FileWriter(new File(saveTo), false);
        } catch (IOException e1) {
            e1.printStackTrace();
        }

        try {
            fwrite.write(area.getText());
            fwrite.close();
        } catch (IOException e1) {
            e1.printStackTrace();
        }
        System.out.println("Saved " + currentFile);
    }

    /*
     * Used with the caret position display; the actual output
     */
    private void updateStatus(int linenumber, int columnnumber) {
        status.setText(linenumber + ":" + columnnumber);
    }

    /*
     * Loads a file to JTextArea area from a String path
     */
    static void loadFile(String filepath) {
        try {
            area.setText(readFile(filepath, Charset.defaultCharset()));
            filenameLabel.setText(new File(filepath).getName());
            currentFile = filepath;
        } catch (IOException e1) {
            e1.printStackTrace();
        }
    }

    /*
     * Reads a file from a String path with Charset encoding and returns it as a
     * String
     */
    static String readFile(String path, Charset encoding) throws IOException {
        byte[] encoded = Files.readAllBytes(Paths.get(path));
        return new String(encoded, encoding);
    }

    /*
     * Returns a string of an InputStream as a string
     */
    static String convertStreamToString(java.io.InputStream is) {
        scanner = new java.util.Scanner(is);
        java.util.Scanner s = scanner.useDelimiter("\\A");
        return s.hasNext() ? s.next() : "";
    }

    /*
     * Runs the current file as Python in cmd.
     */
    public void runPython(String cmdPrefix) {
        Runtime rt = Runtime.getRuntime();
        String pyCmd = cmdPrefix + " " + currentFile;
        System.out.println(osType);
        try {
            rt.exec("cmd.exe /c start cmd.exe /k \"" + pyCmd + "\"");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    /*
     * Shows a popup
     */
    @SuppressWarnings("unused")
    private static void addPopup(final Component component, final JPopupMenu popup) {
        component.addMouseListener(new MouseAdapter() {
            public void mousePressed(MouseEvent e) {
                if (e.isPopupTrigger()) {
                    showMenu(e);
                }
            }

            public void mouseReleased(MouseEvent e) {
                if (e.isPopupTrigger()) {
                    showMenu(e);
                }
            }

            private void showMenu(MouseEvent e) {
                popup.show(e.getComponent(), e.getX(), e.getY());
            }
        });
    }
}

If (understandably) no one wants the read all of this, I'm mainly just looking at the naming conventions and also the way I've used swing, as this is my first swing project.