super method in JLabel inherited class

Question

I am learning Swing GUI. The below program creates a window containing colored labels. I have understood the whole code except the constructor in the Mylabel class which has inherited JLabel. The code is:

`MyLabel`

class MyLabel extends JLabel {

    public MyLabel() {
        super("", null, LEADING);
    }

    @Override
    public boolean isOpaque() {
        return true;
    }
}

`StandardColoursEx`

public class StandardColoursEx extends JFrame {

    public StandardColoursEx() {

        initUI();
    }

    private void initUI() {

        Color[] stdCols = {Color.black, Color.blue, Color.cyan,
            Color.darkGray, Color.gray, Color.green, Color.lightGray,
            Color.magenta, Color.orange, Color.pink, Color.red,
            Color.white, Color.yellow};

        List<JLabel> labels = new ArrayList();

        for (Color col : stdCols) {

            JLabel lbl = createColouredLabel(col);
            labels.add(lbl);
        }

        createLayout(labels.toArray(new JLabel[labels.size()]));

        setTitle("Standard colours");
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

    public JLabel createColouredLabel(Color col) {

        MyLabel lbl = new MyLabel();
        lbl.setMinimumSize(new Dimension(90, 40));
        lbl.setBackground(col);

        return lbl;
    }

    private void createLayout(JLabel[] labels) {

        JPanel pane = (JPanel) getContentPane();
        GroupLayout gl = new GroupLayout(pane);
        pane.setLayout(gl);

        pane.setToolTipText("Content pane");

        gl.setAutoCreateContainerGaps(true);
        gl.setAutoCreateGaps(true);

        gl.setHorizontalGroup(gl.createParallelGroup()
                .addGroup(gl.createSequentialGroup()
                        .addComponent(labels[0])
                        .addComponent(labels[1])
                        .addComponent(labels[2])
                        .addComponent(labels[3]))
                .addGroup(gl.createSequentialGroup()
                        .addComponent(labels[4])
                        .addComponent(labels[5])
                        .addComponent(labels[6])
                        .addComponent(labels[7]))
                .addGroup(gl.createSequentialGroup()
                        .addComponent(labels[8])
                        .addComponent(labels[9])
                        .addComponent(labels[10])
                        .addComponent(labels[11]))
                .addComponent(labels[12])
        );

        gl.setVerticalGroup(gl.createSequentialGroup()
                .addGroup(gl.createParallelGroup()
                        .addComponent(labels[0])
                        .addComponent(labels[1])
                        .addComponent(labels[2])
                        .addComponent(labels[3]))
                .addGroup(gl.createParallelGroup()
                        .addComponent(labels[4])
                        .addComponent(labels[5])
                        .addComponent(labels[6])
                        .addComponent(labels[7]))
                .addGroup(gl.createParallelGroup()
                        .addComponent(labels[8])
                        .addComponent(labels[9])
                        .addComponent(labels[10])
                        .addComponent(labels[11]))
                .addComponent(labels[12])
        );

        pack();
    }

    public static void main(String[] args) {

        EventQueue.invokeLater(() -> {
            StandardColoursEx ex = new StandardColoursEx();
            ex.setVisible(true);
        });
    }
}

Please explain the super constructor inside the MyLabel class and why it is used.

Please use code formatting for code and code snippets, structured documents like HTML/XML or input/output. To do that, select the text and click the `{}` button at the top of the message posting/editing form. — Andrew Thompson, May 06 '18 at 08:57

score 2 · Accepted Answer · answered May 06 '18 at 08:48

2

You are extending the JLabel class, So super for you is JLabel,
here is a link to the docs of JLabel constructor with 3 parameters

answered May 06 '18 at 08:48

Ofer Skulsky

685
4
10

can you explain the third parameter, "HorizontalAlignment". What LEADING does? – Usama Ahmed May 06 '18 at 08:58
1

Have you consulted the [Java Docs for that constructor](https://docs.oracle.com/javase/9/docs/api/javax/swing/JLabel.html#JLabel-java.lang.String-javax.swing.Icon-int-)? – Andrew Thompson May 06 '18 at 09:00
1

horizontalAlignment - One of the following constants defined in SwingConstants: LEFT, CENTER, RIGHT, LEADING or TRAILING. TRAILING = Identifies the trailing edge of text for use with left-to-right and right-to-left languages. LEADING = Identifies the leading edge of text for use with left-to-right and right-to-left languages. – Ofer Skulsky May 06 '18 at 09:00

super method in JLabel inherited class

MyLabel

StandardColoursEx

1 Answers1

`MyLabel`

`StandardColoursEx`