awesome program

package my.pack;

import java.awt.AWTException;
import java.awt.Robot;
import java.awt.event.KeyEvent;
import java.util.function.Consumer;

import org.jnativehook.GlobalScreen;
import org.jnativehook.NativeHookException;
import org.jnativehook.keyboard.NativeKeyEvent;
import org.jnativehook.keyboard.NativeKeyListener;

public class PrintOut {

    static volatile boolean stop = false;

    static volatile String key;

    public static void main(String[] args) {
        try {
            GlobalScreen.registerNativeHook();
        } catch (NativeHookException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        NativeKeyListener listener = new NativeKeyListener() {

            @Override
            public void nativeKeyTyped(NativeKeyEvent arg0) {
            }

            @Override
            public void nativeKeyReleased(NativeKeyEvent arg0) {
            }

            @Override
            public void nativeKeyPressed(NativeKeyEvent arg0) {
                if (arg0.getKeyCode() == 3658) {
                    stop = true;

                    try {
                        Robot robot = new Robot();
                        robot.setAutoDelay(1);
                        System.out.println(KeyEvent.VK_0);

                        Consumer<Integer> press = x -> {
                            robot.keyPress(0x30 + x);
                            robot.keyRelease(0x30 + x);
                        };

                        // a b c d
                        for (int a = 0; a <= 0; a++) {
                            for (int b = 0; b <= 9; b++) {
                                for (int c = 0; c <= 9; c++) {
                                    for (int d = 0; d <= 9; d++) {
                                        if (a == 0) {
                                            if (b == 0) {
                                                if (c == 0) {
                                                    press.accept(d);
                                                }
                                                else {
                                                    press.accept(c);
                                                    press.accept(d);
                                                }
                                            }
                                            else {
                                                press.accept(b);
                                                press.accept(c);
                                                press.accept(d);
                                            }
                                        }
                                        else {
                                            press.accept(a);
                                            press.accept(b);
                                            press.accept(c);
                                            press.accept(d);
                                        }

                                        press.accept(KeyEvent.VK_ENTER - 0x30);
                                    }
                                }
                            }
                        }

                        System.exit(0);
                    } catch (AWTException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            }
        };

        GlobalScreen.addNativeKeyListener(listener);

    }
}