Java Swing Component

I am quite new to Java Swing and layouts. I want to create a component like this:

Comp 3 spans the height of 1 and 2. So, I imagine I will have to use overlay layout to position comp 3 behind 1 and 2. I want them to resize in these same proportions (they can be arbitrarily decided). How can I achieve this?

You can use a combination of one or multiple GridBagLayout layout managers.<br>GridBagLayout allows you to place your elements in a grid-like manner by specifiying the proportions and positioning using the class GridBagConstraints.

public void setupLayout() {
    JPanel container = new JPanel(); // the main holder of the elements
    // The numbered panels according to your screenshot
    JPanel panel1 = new JPanel(), panel2 = new JPanel(),
            panel3 = new JPanel(), panel4 = new JPanel();
	panel1.setBackground(Color.RED); // giving them colors for better visualization
	panel2.setBackground(Color.BLUE);
	panel3.setBackground(Color.YELLOW);
	panel4.setBackground(Color.GREEN);

    container.setLayout(new GridBagLayout());
    GridBagConstraints gbc = new GridBagConstraints();
    gbc.anchor = GridBagConstraints.CENTER;
	gbc.fill = GridBagConstraints.BOTH;
    gbc.gridwidth = gbc.gridheight = 1;
	gbc.weightx = 1;
	gbc.gridx = 0; gbc.gridy = 0; gbc.weighty = 0.2;
	panel.add(panel1,gbc);

	gbc.gridy = 1; gbc.weighty = 0.3;
	panel.add(panel2,gbc);

	gbc.gridy = 2; gbc.weighty = 0.5;
	panel.add(panel3,gbc);

	gbc.gridx = 1; gbc.gridy = 0; gbc.gridheight = 3;
	panel.add(panel4,gbc);

    // Code to place your container in a frame or whatever usage you have for it...
}

The properties gridx and gridy specify the position you are on the grid.<br>weightx and weighty specify how much space (on a 0 to 1 proportion) they take up.
<br>Unlike gridwidth and gridheight they specify how much does a cell take up relative to other cells so a cell will take up a space equal to the space that gridheight cells take up vetically or gridwidth cells take up horizontally.<br>So, to be explained in action, since panel1 is set to weighty = 0.2, panel2 is set to weighty = 0.3 and panel3 is set to weighty = 0.5 we're saying that whatever cell is on the first row, will always take 0.2 of the vertical space, second row 0.3 of vertical space and third row half (0.5) the vertical space, therefore panel4 will take up the same space as how many cells heights sum up to the prior, if panel4 was set to gridheight = 2, it will take as much space as two rows take up, since in this example it's placed on the first row, it will take up therefore a space equivalent to that of the first and second rows, which is half the vertical space (0.2 + 0.3), but since we set it to 3 which is also the maximum number of rows in this example, it will take up all of the vertical space.<br>Mixing up gridwidth/gridheight and weightx/weighty is commmon therefore you have to be aware of the difference.<br>Note that using the gridwidth/gridheight/weightx/weighty will only "reserve" the space you're specifying, and the elements will be placed inside that spaced anchored to the side specified in the anchor property.
<br>In order to make the elements scale up to their reserved space we set gbc.fill = GridBagConstraints.BOTH where BOTH stands for filling up the space both horizontally and vertically (the other three choices being, clearly, GridBagConstraints.HORIZONTAL, GridBagConstraints.VERTICAL and GridBagConstraints.NONE which is the default value that represents no filling at all.