Null is returned if none of the components in this application has the focus : Focus « Swing Event « Java Tutorial

1. Java Tutorial
2. Swing Event
3. Focus

import java.awt.Component;
import java.awt.KeyboardFocusManager;

public class Main {
  public static void main() {

    Component compFocusOwner = KeyboardFocusManager.getCurrentKeyboardFocusManager()
        .getFocusOwner();

  }
}

15.15.Focus
	15.15.1.	No Focus Button
	15.15.2.	Focus auto-setting
	15.15.3.	Focus Traversal: requestFocusInWindow
	15.15.4.	Moving focus to the next component: focusNextComponent()
	15.15.5.	Restricting the Focus Cycle
	15.15.6.	Request Focus inside a window
	15.15.7.	Predefined Focus Traversal Policies
	15.15.8.	Reversing Focus Traversal
	15.15.9.	KeyboardFocusManager
	15.15.10.	Use KeyboardFocusManager
	15.15.11.	Use FocusTraversalPolicy
	15.15.12.	Finding the Next Focusable Component
	15.15.13.	Find the previous focusable component
	15.15.14.	Determining If a Focus Lost Is Temporary or Permanent
	15.15.15.	Null is returned if none of the components in this application has the focus
	15.15.16.	Null is returned if none of the windows in this application has the focus
	15.15.17.	Changes the focus traversal keys for the entire application.
	15.15.18.	Change the backward focus traversal keys for the application
	15.15.19.	Change the forward focus traversal keys for a component
	15.15.20.	JComponent.setFocusTraversalKeys(int arg0, Set arg1)
	15.15.21.	KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS
	15.15.22.	Setting Focus Traversal Keys for the Entire Application
	15.15.23.	KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS
	15.15.24.	KeyboardFocusManager.getCurrentKeyboardFocusManager().getDefaultFocusTraversalKeys(KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS)
	15.15.25.	KeyboardFocusManager.getCurrentKeyboardFocusManager().clearGlobalFocusOwner()
	15.15.26.	Determining the Opposite Component of a Focus Event
	15.15.27.	Listening to All Key Events Before Delivery to Focused Component
	15.15.28.	Removing the Focus from the Application
	15.15.29.	Use isFocusOwner to determine whether a particular component has the focus
	15.15.30.	JComponent.WHEN_IN_FOCUSED_WINDOW
	15.15.31.	Make sure that my Text field has the focus when a JFrame is created