@Override
	public void focusGained(FocusEvent e) {
		Component comp = e.getComponent();
		for (int i = 0; i < 4; i++) {
			if (listingPanels[i].getFieldPanel() == comp) {
				currProgIndex = i;
			}
		}
	}
@see java.awt.event.FocusListener#focusGained(java.awt.event.FocusEvent)
Ghidra/Features/Base/src/main/java/ghidra/app/merge/tool/ListingMergePanel.java