GUI 4 - Tiny Window with a JLabel

The main program is like the previous example, after changing the GUI class name, so it isn't repeated here.

JFrame constructor and methods

JPanel constructor and methods

JLabel constructor and methods

content.add(new JLabel("Name"));

FlowLayout - Left to right, top to bottom

Making a good component layout can be a lot of work. Java uses layout managers to implement various layout strategies. The simplest is FlowLayout, which simply centers the components adding them from left to right, and if necessary flowing them to another line. This example only shows one component, but you'll see more in the next example. The only thing you do with a layout object is create it with new and use it to set the layout of a JPanel.

Source code - a subclass of JFrame

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// File   : gui-tutorial/tw4/TinyWindow4.java
// Purpose: Create a window with a JLabel.
// Author : Fred Swartz - 2006-11-09

import java.awt.*;           // Needed for FlowLayout.           //Note 1
import javax.swing.*;

////////////////////////////////////////////////////// class TinyWindow4
class TinyWindow4 extends JFrame {

    //============================================================= main
    public static void main(String[] args) {
        TinyWindow4 window = new TinyWindow4();
        window.setVisible(true);
    }

    //======================================================= constructor
    public TinyWindow4() {
        //... Create content panel, set layout
        JPanel content = new JPanel();                           //Note 2
        content.setLayout(new FlowLayout());   // Use FlowLayout //Note 3

        //... Add one label to the content pane.
        JLabel greeting = new JLabel("We come in peace.");       //Note 4
        content.add(greeting);                 // Add label      //Note 5

        //... Set window (JFrame) characteristics
        setContentPane(content);                                 //Note 6
        pack();                                // Do layout.     //Note 7
        setTitle("Tiny Window using JFrame Subclass");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);           // Center window.
    }
}

Notes

1. Some elements of the GUI interface are defined in the older AWT package, although the components and containers (starting with "J") are all part of Swing.
2. Create a new JPanel to hold the components for the window's content pane.
3. A layout manager should be explicitly set for the content pane.
4. Create a JLabel.
5. Add the label to the content pane. There really was no reason to assign the JLabel to a variable - the new JLabel(..) could have been an argument to add(...).
6. The content pane of this JFrame is now set to the JPanel that we created earlier, named "content".
7. After the content pane of the JFrame has been set and populated with components, it's necessary to call pack() to do the layout -- it sets the location and size of each component.

Creating a new content pane rather than using the defualt

Every window (JFrame) has a content pane that arranges the components which have been added to it according to the specified layout. The content pane is usually implemented as a JPanel.

Altho every JFrame comes with a predefined content pane, these examples create a new JPanel for the content pane. If you're interested in the issues and options for handling the content pane, look at Content Pane (or Content Pain?), but it isn't necessary.