Container Size
When calculating the preferred and minimum size values for a container,
FlowLayout can't make any assumptions about the width of the
container or about how many rows of components should be created. Instead,
the size values are calculated so that the container will be wide enough to
contain all child components in a single row. For example, the
preferred width value returned by a FlowLayout is determined
by adding three values:
- The left and right inset values of the container
- The amount of space needed to provide horizontal gaps
- The sum of all child components' preferred widths
In other words, a FlowLayout's preferred width is the amount
of horizontal space needed to display all its child components from end-to-
end on a single row using their preferred sizes.
To determine the container's preferred height, FlowLayout
first identifies the preferred height of the tallest component in the
container. The container's preferred height is then calculated as the sum
of largest component height, the number of pixels needed to provide
vertical gaps at the top and bottom edges of the container, and the
container's top and bottom inset values.
The value returned for a container's minimum size by a
FlowLayout is calculated in essentially the same way as the
preferred size, but is done using the minimum sizes of the components in
the container instead of their preferred sizes.
GridLayout
This layout manager divides the available space into a grid of
cells, evenly allocating the space among all the cells in the grid
and placing one component in each cell. For example, in the following code,
four buttons are added to a container that uses a GridLayout:
import java.awt.*;
import javax.swing.*;
public class GridSizeTest extends JFrame {
public static void main(String[] args) {
GridSizeTest gst = new GridSizeTest();
gst.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
gst.pack(); // pack() makes the window the right
gst.setVisible(true); // size for all it's components to fit
}
public GridSizeTest() {
Container pane = getContentPane();
pane.setLayout(new GridLayout(2, 2));
JButton button = new JButton("First");
pane.add(button);
button = new JButton("Second with a very long name");
pane.add(button);
button = new JButton("Hi");
button.setFont(new Font("Courier", Font.PLAIN, 36));
pane.add(button);
button = new JButton("There");
pane.add(button);
}
}
When this code is compiled and executed, it produces a display like the one
shown below. Notice that all of the buttons are allocated the same amount
of space, even though one button's label is wider than the others and
another has a label that's much taller than the rest:
As this example illustrates, GridLayout is useful when some
rectangular portion of your interface contains adjacent components that
should all be assigned the same size and when the amount of space between
those components is consistent. For instance, you might use a
GridLayout to create a panel that contains a row of buttons
that are all the same size and which have the same amount of space between
one another.
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