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Implements VetoableChangeListener to block focus change events

import java.awt.Component; import java.awt.KeyboardFocusManager; import java.beans.PropertyChangeEvent; import java.beans.PropertyVetoException; import java.beans.VetoableChangeListener; public class Main {   public static void main(String[] argv) {     KeyboardFocusManager.getCurrentKeyboardFocusManager().addVetoableChangeListener(         new FocusVetoableChangeListener());   } } class FocusVetoableChangeListener implements VetoableChangeListener {   public void vetoableChange(PropertyChangeEvent evt) throws PropertyVetoException {     Component oldComp = (Component) evt.getOldValue();     Component newComp = (Component) evt.getNewValue();     if ("focusOwner".equals(evt.getPropertyName())) {       if (oldComp == null) {         System.out.println(newComp.getName());       } else {         System.out.println(oldComp.getName());       }     } else if ("focusedWindow".equals(evt.getPropertyName())) {       if (oldComp == null) {         System.out.println(newComp.getName());       } else {         System.out.println(oldComp.getName());       }     }     boolean vetoFocusChange = false;     if (vetoFocusChange) {       throw new PropertyVetoException("message", evt);     }   } }