import java.awt.Toolkit;
import java.awt.datatransfer.Clipboard;
import java.awt.datatransfer.Transferable;
import java.util.Stack;

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

public class Test3 implements NativeKeyListener {

Clipboard sysClip = Toolkit.getDefaultToolkit().getSystemClipboard();
Stack<Transferable> clipStack = new Stack<>();

public static void main(String[] args) {
    try {
        GlobalScreen.registerNativeHook();
    } catch (NativeHookException ex) {
        System.err
                .println("There was a problem registering the native hook.");
        System.err.println(ex.getMessage());

        System.exit(1);
    }
    Test2 t2 = new Test2();
    // Construct the example object and initialze native hook.
    GlobalScreen.getInstance().addNativeKeyListener(t2);
}

@Override
public void nativeKeyPressed(NativeKeyEvent ev) {
    // Copy
    if (ev.getKeyCode() == NativeKeyEvent.VK_C
            && NativeInputEvent.getModifiersText(ev.getModifiers()).equals(
                    "Ctrl")) {
        // Clip the pop
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        clipStack.push(sysClip.getContents(null));

        System.out.println("Ctrl+C : Stack(" + clipStack.size() + ")");
    }
    // Paste
    if (ev.getKeyCode() == NativeKeyEvent.VK_V
            && NativeInputEvent.getModifiersText(ev.getModifiers()).equals(
                    "Ctrl")) {
        // Clip the pop
        try {
            Thread.sleep(100);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        if (clipStack.size() > 1) {
            sysClip.setContents(clipStack.pop(), null);
        } else
            sysClip.setContents(clipStack.peek(), null);

        System.out.println("Ctrl+V : Stack(" + clipStack.size() + ")");
    }
}

@Override
public void nativeKeyReleased(NativeKeyEvent e) {

}

@Override
public void nativeKeyTyped(NativeKeyEvent e) {

}

}