How to delete all characters in a text box using SWT?

Hi,
I have GUI that I create using SWT. I have a text box in this GUI where I can type some characters.

I have a button in the toolbar that is supposed to delete everything in this text box.

This is how I create this text box. I have a TxtFocusListener.java class as shown below:

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.FocusEvent;
import org.eclipse.swt.events.FocusListener;
import org.eclipse.swt.widgets.Composite;
import org.eclipse.swt.widgets.Text;

public class TxtFocusListener implements FocusListener {
    
    static final String introText = "Use the buttons above to select files/directories";
    private Composite parent;

    public TxtFocusListener(Composite parent) {
        this.parent = parent;
    }

    @Override
    public void focusGained(FocusEvent e) {
        Text t = (Text)e.widget;
        if (t.getText().equalsIgnoreCase(introText)) {
            t.setText("");
            t.setForeground(parent.getDisplay().getSystemColor(SWT.COLOR_BLACK));
        }
    }

    @Override
    public void focusLost(FocusEvent e) {
        Text t = (Text)e.widget;
        if (t.getText().equalsIgnoreCase("")) {
            t.setText(introText);
            t.setForeground(parent.getDisplay().getSystemColor(SWT.COLOR_GRAY));
        }
    }

}

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And this is how I create the text box:

  GridLayout groupLayout = new GridLayout();
        GridData groupGD = new GridData(GridData.FILL_BOTH);
        Group groupText = new Group(compTab1, SWT.NONE);
        groupText.setLayout(groupLayout);
        groupText.setLayoutData(groupGD);
        groupText.setText("Files in List");
       
        GridData txtGridData = new GridData(GridData.FILL_BOTH);
        Text txt = new Text(groupText, SWT.MULTI | SWT.BORDER | SWT.WRAP | SWT.V_SCROLL);
        TxtFocusListener txtFL = new TxtFocusListener(compTab1);
        txt.setLayoutData(txtGridData);
        txt.addFocusListener(txtFL);
        txt.setText(TxtFocusListener.introText); txt.setForeground(compTab1.getDisplay().getSystemColor(SWT.COLOR_GRAY));

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