what is exactly a JPanel,JFrame,JLayeredPane and JRootpane [closed]

Question

i am new to java while reading i came across various frames and panels,confused between JFrame ,JLayeredPane ,JRootPane and JPannel what is diffrence between them is it possible to use both JFrame and JPanel in single class.

Answer 1

Take a look at the picture here

from the German Java Tutorial page.

Some details

• The JFrame is the window, which is shown as a Top Level Window of Your operating system.
• JFrame is composed of more than one functional elements. One of them, for example, eases the burden of implementing the tooltips correctly: the LayeredPane. Among others, it takes care that the tooltips are drawn always on top of everything else.
• The ContentPane is the most sensible place to put the main content.
• The JPanel is an universal container. The number one class You'd use to put buttons and forms into.

The official Swing tutorial sums up the design very well.

Let's do a minimal example:

import javax.swing.JFrame;

public class SomeFrame {

    public static void main(String [] as) {
        // let's make it as simple as possible
        JFrame jFrame = new JFrame("Hi!");
        jFrame.setVisible(true);
    }
}

The code above would produce a Frame, but not really usable:

Let's make it a little bigger, only to expose the title:

    JFrame jFrame = new JFrame("Hi!");
    jFrame.setSize(200, 50);
    jFrame.setVisible(true);

Result:

Now, lets see if we can add any component into the frame. Let's add a label - in Swing it's realized by the class JLabel:

    JFrame jFrame = new JFrame("Hi!");
    jFrame.setSize(200, 100);
    JLabel label = new JLabel("Hello Swing!");
    jFrame.add(label);
    jFrame.setVisible(true);

Ok, so what we have done? Added the JLabel into the JFrame. If You'll look into the Swing code, internally the JFrame.add() method adds the component into the ContentPane. So the above code is equivalent to:

    JFrame jFrame = new JFrame("Hi!");
    jFrame.setSize(200, 100);
    JLabel label = new JLabel("Hello Swing!");
    jFrame.getContentPane().add(label);         // <----
    jFrame.setVisible(true);

You can check by yourself that the ContentPane is realized internally by a JPanel. It's in the Swing code:

// this invocation...
JFrame jFrame = new JFrame("Hi!");

// effectively invokes following methods:

public JFrame(String title) throws HeadlessException {
    // ...
    frameInit();
}

protected void frameInit() {
    // ...
    setRootPane(createRootPane());
    // ...
}

protected JRootPane createRootPane() {
    JRootPane rp = new JRootPane();
    // ...
}

public JRootPane() {
    setGlassPane(createGlassPane());
    setLayeredPane(createLayeredPane());
    setContentPane(createContentPane());
    // ...
}

protected Container createContentPane() {
    JComponent c = new JPanel();             // <----
    // ...
    return c;
}