Layout for label and button programmatically

From the Java trails of SpringLayout (pretty much the first line, actually):

The SpringLayout class was added in JDK version 1.4 to support layout in GUI builders. SpringLayout is a very flexible layout manager that can emulate many of the features of other layout managers. SpringLayout is, however, very low-level and as such you really should only use it with a GUI builder, rather than attempting to code a spring layout manager by hand. (Emphasis added.)

I've been programming professionally in Java for years now and even I won't program SpringLayout by hand. My recommendation is to use the MigLayout library instead. Their API is much simpler for layout-by-hand code and can produce very near-native layouts. I've been using it for a long time now, and I prefer it over anything else I've tried. It's especially nice when used in conjunction with Java's BorderLayout due to the way space-filling works. I highly recommend it.

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First things first:

1. MigLayout is cell-based, but also supports splitting and spanning cells. If you've ever worked with HTML or Excel, you should know what that means. It's pretty self-explanatory.
2. MigLayout's default method of input is strings, and they're the simplest to understand, but they also have a very good API for creating layouts as well.
3. MigLayout supports far more than I'll ever be able to cover in an SO question, so follow the link above and check out the quick start guide and cheat sheet. They're by far the best resource for what you can put in your constraints.

Here is an example using MigLayout to produce a similar layout to the example image you posted:

public static void main(String[] args) {
    JFrame frame = new JFrame("Testing MigLayout");
    JPanel contentPane = new JPanel(new MigLayout("fillx"));

    // Row 1
    JLabel areaLabel = new JLabel("Area of Triangle");
    areaLabel.setFont(areaLabel.getFont().deriveFont(16.0f));
    areaLabel.setHorizontalAlignment(JLabel.CENTER);
    contentPane.add(areaLabel, "spanx, growx, wrap");
    // wrap indicates a new row

    // Row 2
    JLabel side1Label = new JLabel("Side 1:");
    contentPane.add(side1Label, "alignx trailing");
    JTextField side1Field = new JTextField();
    side1Field.setColumns(6);
    contentPane.add(side1Field, "alignx leading, wrap");

    // Row 3
    JLabel side2Label = new JLabel("Side 2:");
    contentPane.add(side2Label, "alignx trailing");
    JTextField side2Field = new JTextField();
    side2Field.setColumns(6);
    contentPane.add(side2Field, "alignx leading, wrap");

    // Row 4
    JLabel side3Label = new JLabel("Side 3:");
    contentPane.add(side3Label, "alignx trailing");
    JTextField side3Field = new JTextField();
    side3Field.setColumns(6);
    contentPane.add(side3Field, "alignx leading, wrap");

    // Row 5
    JButton calculateButton = new JButton("Calculate Area");
    contentPane.add(calculateButton, "spanx, growx");

    frame.setContentPane(contentPane);
    // Resizes automatically
    frame.pack();
    // Centers automatically
    frame.setLocationRelativeTo(null);
    // Exit when the frame is closed
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    frame.setVisible(true);
}

And its output:

This is without all the logic, of course, but it still shows MigLayout's power. When you start getting into more complex applications and want components to expand and contract with the window, MigLayout does very well. If you've ever used GridBadLayout, you'll notice that MigLayout is just a suped up version of it.

For references about what all the individual pieces of this are, just look at the cheat sheet. There's an explanation for every piece I used. Specifically, anything declared in the MigLayout constructor (here, "fillx") is a layout constraint, and anything declared in the add methods (such as "spanx" and "wrap") are component constraints. There's more you can do with practice and experimentation to get just the right combination that creates an excellent GUI.

That being said, there's always other, simpler layout managers like GridLayout or BoxLayout. For simple applications like yours, those layout managers are perfectly fine. When you start getting into the more intensive applications, I recommend breaking into MigLayout. For reading up on those, I recommend the Java trails. There's a visual guide to layouts on there as well, and you can use that as a jumping-off point. I recommend sticking with these for layout-by-hand:

• BorderLayout
• BoxLayout
• CardLayout
• FlowLayout
• GridBagLayout
• GridLayout