import org.eclipse.swt.SWT;
import org.eclipse.swt.custom.StyledText;
import org.eclipse.swt.events.KeyEvent;
import org.eclipse.swt.events.KeyListener;
import org.eclipse.swt.graphics.FontMetrics;
import org.eclipse.swt.graphics.GC;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.widgets.Caret;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;

public class CaretTest {

	public static boolean overwriteMode = false;
	
	public static void main(String[] args) {
		Display display = new Display();
		Shell shell = new Shell(display);
		shell.setLayout(new FillLayout());
		shell.setSize(200, 200);
		final StyledText textWidget = new StyledText(shell, SWT.BORDER);
		Caret caret = new Caret(textWidget, SWT.NONE);
		caret.setBounds(10, 10, 1, 16);
		
		textWidget.addKeyListener(new KeyListener() {
			
			public void keyReleased(KeyEvent arg0) {
			}
			
			public void keyPressed(KeyEvent event) {
				if (event.keyCode == SWT.INSERT) {
					setOverwriteMode(!isOverwriteMode());
					
					changeCaretPresentation(textWidget, isOverwriteMode());
				}
			}

			private void setOverwriteMode(boolean value) {
				overwriteMode = value;
			}

			private boolean isOverwriteMode() {
				return overwriteMode;
			}
		});
		
		shell.open();
		while (!shell.isDisposed()) {
			if (!display.readAndDispatch())
				display.sleep();
		}
		display.dispose();
	}
	
	public static void changeCaretPresentation(StyledText textWidget, boolean overwriteMode) {
		Caret defaultCaret = textWidget.getCaret();
		GC graphicsContext = new GC(textWidget);
		FontMetrics fontMetrics = graphicsContext.getFontMetrics();
		
		if (overwriteMode) { //  block mode
			defaultCaret.setBounds(defaultCaret.getLocation().x, defaultCaret.getLocation().y, fontMetrics.getAverageCharWidth(), fontMetrics.getHeight());
		}
		else { // beam mode
			defaultCaret.setBounds(defaultCaret.getLocation().x, defaultCaret.getLocation().y, 1, fontMetrics.getHeight());
		}
	}
}