Task: GUI enabling_disabling of controls
C#: using System; 
using System.ComponentModel; 
using System.Windows.Forms; 

class RosettaInteractionForm : Form
{    

    
    
    class NumberModel: INotifyPropertyChanged
    {
        
        public event PropertyChangedEventHandler PropertyChanged = delegate {};

        int _value;
        public int Value
        {
            get { return _value; }
            set 
            { 
                _value = value;
                
                PropertyChanged(this, new PropertyChangedEventArgs("Value"));
            }
        }
    }

    NumberModel model = new NumberModel{ Value = 0};
    
    RosettaInteractionForm()    
    {
        
        var tbNumber = new MaskedTextBox
                        { 
                            Mask="0000",            
                            ResetOnSpace = false,   
                            Dock = DockStyle.Top    
                        };
        
        tbNumber.DataBindings.Add("Text", model, "Value");
        var enabledIfZero = new Binding("Enabled", model, "Value");
        EnableControlWhen(tbNumber, value => value == 0);

        var btIncrement = new Button{Text = "Increment", Dock = DockStyle.Bottom};
        btIncrement.Click += delegate
                        {
                            model.Value++;
                        };
        EnableControlWhen(btIncrement, value => value < 10);
        var btDecrement = new Button{Text = "Decrement", Dock = DockStyle.Bottom};
        btDecrement.Click += delegate
                        {
                            model.Value--;
                        };
        EnableControlWhen(btDecrement, value => value > 0);
        Controls.Add(tbNumber);
        Controls.Add(btIncrement);
        Controls.Add(btDecrement);
    }

    
    void EnableControlWhen(Control ctrl, Func<int, bool> predicate)
    {
        
        var enabledBinding = new Binding("Enabled", model, "Value");
        
        enabledBinding.Format += (sender, args) =>
            {
                
                if (args.DesiredType != typeof(bool)) return;
                
                args.Value = predicate((int)args.Value);
            };
        
        ctrl.DataBindings.Add(enabledBinding);
    }

    static void Main()
    {
        Application.Run(new RosettaInteractionForm());
    }
}

Java: import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

public class Interact extends JFrame{
	final JTextField numberField;
	final JButton incButton, decButton;
	
	public Interact(){
		
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
		
		numberField = new JTextField();
		incButton = new JButton("Increment");
		decButton = new JButton("Decrement");
		
		numberField.setText("0");
		decButton.setEnabled(false);
		
		
		numberField.addKeyListener(new KeyListener(){
			@Override
			public void keyTyped(KeyEvent e) {
				
				if(!Character.isDigit(e.getKeyChar())){
					
					e.consume();
				}else if(Character.isDigit(e.getKeyChar())){
					
					
					
					SwingUtilities.invokeLater(new Runnable() {
						@Override
						public void run() {
							String text = numberField.getText();
							if(text.isEmpty()){
								numberField.setText("0");
								decButton.setEnabled(false);
								incButton.setEnabled(true);
								return;
							}
							if(Long.valueOf(text) <= 0){
								decButton.setEnabled(false);
								incButton.setEnabled(true);
							}else if(Long.valueOf(text) >= 10){
								incButton.setEnabled(false);
								decButton.setEnabled(true);
							}else{
								incButton.setEnabled(true);
								decButton.setEnabled(true);
							}
						}
					});
				}
			}
			@Override
			public void keyReleased(KeyEvent e){}
			@Override
			public void keyPressed(KeyEvent e){
				
				
				if(e.getKeyCode() == KeyEvent.VK_BACK_SPACE ||
						e.getKeyCode() == KeyEvent.VK_DELETE){
					SwingUtilities.invokeLater(new Runnable() {
						@Override
						public void run() {
							String text = numberField.getText();
							if(text.isEmpty()){
								numberField.setText("0");
								decButton.setEnabled(false);
								incButton.setEnabled(true);
								return;
							}
							if(Long.valueOf(text) <= 0){
								decButton.setEnabled(false);
								incButton.setEnabled(true);
							}else if(Long.valueOf(text) >= 10){
								incButton.setEnabled(false);
								decButton.setEnabled(true);
							}else{
								incButton.setEnabled(true);
								decButton.setEnabled(true);
							}
						}
					});
				}
			}
		});
		
		
		incButton.addActionListener(new ActionListener(){
			@Override
			public void actionPerformed(ActionEvent e) {
				String text = numberField.getText();
				numberField.setText((Long.valueOf(text) + 1) + "");
				if(Long.valueOf(text) + 1 >= 10){
					incButton.setEnabled(false);
				}
				
				if(Long.valueOf(text) + 1 > 0){
					decButton.setEnabled(true);
				}
			}
		});
		
		
		decButton.addActionListener(new ActionListener(){
			@Override
			public void actionPerformed(ActionEvent e) {
				String text = numberField.getText();
				numberField.setText((Long.valueOf(text) - 1) + "");
				if(Long.valueOf(text) - 1 <= 0){
					decButton.setEnabled(false);
				}
				
				if(Long.valueOf(text) - 1 < 10){
					incButton.setEnabled(true);
				}
			}
		});
		
		
		setLayout(new GridLayout(2, 1));
		
		
		JPanel buttonPanel = new JPanel();
		
		
		buttonPanel.setLayout(new GridLayout(1, 2));
		
		buttonPanel.add(incButton);
		buttonPanel.add(decButton);
		
		
		add(numberField);
		add(buttonPanel);
		
		pack();
		
	}

	public static void main(String[] args){
		new Interact().setVisible(true);
	}
}