ResultsPanel myPanel = new ResultsPanel(pnlResults);  //pnlResults is an existing JPanel
myPanel.addLabel(pnlResults);

public class ResultsPanel extends JPanel {

    JPanel myPanel;

    public ResultsPanel(JPanel thisPanel) {
        myPanel = thisPanel;
    }

    public void addLabel(JPanel myResults) {
        JLabel myLabel = new JLabel("test", JLabel.LEFT);
        myPanel.setLayout(new FlowLayout());
        add(myLabel);
    }

}

JLabel myLabel = new JLabel("test");
pnlResults.add(myLabel);

JLabel label = new JLabel("Test text");//initialize the label
//do some stuff with label here maybe...
panel.add(label);//now add it

JFrame frame = new JFrame("Basic Swing");//Make a frame
    frame.setSize(300, 300);//Give it a size
    frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);//Make it go away on close
    JPanel panel = new JPanel();//Make a panel
    frame.add(panel);//Add it to your frame

    JLabel label = new JLabel("Hello StackOverflow!");//Make a label
    panel.add(label);//Add it to the panel (which is on the frame)

    frame.setVisible(true);//Show the frame

JLabel myLabel = new JLabel("test text");
myLabel.setSize(myLabel.getPreferredSize());
panel.add(myLabel);
panel.revalidate();
panel.repaint();

public void addLabel() {
    myPanel.setBorder(new TitledBorder("test"));
}