Top to bottom left to right layout netbeans năm 2024

By creating one or more lightweight containers that use

Box.createRigidArea(size)

3, you can achieve some layouts for which the more complex

Box.createRigidArea(size)

8 is often used.

Box.createRigidArea(size)

3 is also useful in some situations where you might consider using

Box.createHorizontalGlue()

0 or

Box.createHorizontalGlue()

1. One big difference between

Box.createRigidArea(size)

3 and the existing AWT layout managers is that

Box.createRigidArea(size)

3 respects each component's maximum size and X/Y alignment. We'll discuss that later.

The following figure shows a GUI that uses two instances of

Box.createRigidArea(size)

3. In the top part of the GUI, a top-to-bottom box layout places a label above a scroll pane. In the bottom part of the GUI, a left-to-right box layout places two buttons next to each other. A

Box.createHorizontalGlue()

1 combines the two parts of the GUI and ensures that any excess space is given to the scroll pane.

The following code, taken from

Box.createHorizontalGlue()

6

, lays out the GUI. This code is in the constructor for the dialog, which is implemented as a

Box.createHorizontalGlue()

7 subclass. The bold lines of code set up the box layouts and add components to them.

JScrollPane listScroller = new JScrollPane(list);

listScroller.setPreferredSize(new Dimension(250, 80)); listScroller.setMinimumSize(new Dimension(250, 80)); listScroller.setAlignmentX(LEFT_ALIGNMENT); ... //Lay out the label and scroll pane from top to bottom. JPanel listPane = new JPanel();

listPane.setLayout(new BoxLayout(listPane, BoxLayout.Y_AXIS));

JLabel label = new JLabel(labelText);

listPane.add(label); listPane.add(Box.createRigidArea(new Dimension(0,5))); listPane.add(listScroller);

listPane.setBorder(BorderFactory.createEmptyBorder(10,10,10,10)); //Lay out the buttons from left to right. JPanel buttonPane = new JPanel();

buttonPane.setLayout(new BoxLayout(buttonPane, BoxLayout.X_AXIS));

buttonPane.setBorder(BorderFactory.createEmptyBorder(0, 10, 10, 10));

buttonPane.add(Box.createHorizontalGlue()); buttonPane.add(cancelButton); buttonPane.add(Box.createRigidArea(new Dimension(10, 0))); buttonPane.add(setButton); //Put everything together, using the content pane's BorderLayout. Container contentPane = getContentPane(); contentPane.add(listPane, BorderLayout.CENTER); contentPane.add(buttonPane, BorderLayout.SOUTH);

The first bold line creates a top-to-bottom box layout and sets it up as the layout manager for

Box.createHorizontalGlue()

8. The two arguments to the

Box.createRigidArea(size)

3 constructor are the container that it manages and the axis along with the components will be laid out. The next three bold lines add the label and scroll pane to the container, separating them with a rigid area -- an invisible lightweight component used to add space between components. In this case, the rigid area has no width and puts exactly 5 pixels between the label and scroll pane. Rigid areas are discussed later, in .

The next chunk of bold code creates a left-to-right box layout and sets it up for the

Box.createVerticalGlue()

0 container. Then the code adds two buttons to the container, using a rigid area to put 10 pixels between the buttons. To place the buttons at the right side of their container, the first component added to the container is glue. This glue is an invisible lightweight component that grows as necessary to absorb any extra space in its container. Glue is discussed in .

As an alternative to using invisible components, you can sometimes use empty borders to create space around components. For example, the preceding code snippet uses empty borders to put 10 pixels between all sides of the dialog and its contents, and between the two parts of the contents. Borders are completely independent of layout managers. They're simply how Swing components draw their edges. See How to Use Borders

for more information.

The following sections discuss

Box.createRigidArea(size)

3 in more detail:

Don't let the length of the

Box.createRigidArea(size)

3 discussion scare you! You can probably use

Box.createRigidArea(size)

3 with the information you already have. If you run into trouble or you want to take advantage of

Box.createRigidArea(size)

3's power, read on.

Box Layout Features

As we said before, a

Box.createRigidArea(size)

3 arranges components either from top to bottom or from left to right. As it arranges components, the box layout takes the components' alignments and minimum, preferred, and maximum sizes into account. In this section, we'll talk about top-to-bottom (Y axis) layout. The same concepts apply to left-to-right layout. You simply substitute X for Y, height for width, and so on.

When a

Box.createRigidArea(size)

3 lays out components from top to bottom, it tries to size each component at the component's preferred height. If the amount of vertical space is not ideal, the box layout tries to adjust each components' height so that the components fill the available amount of space. However, the components might not fit exactly, since

Box.createRigidArea(size)

3 respects each component's requested minimum and maximum heights. Any extra space appears at the bottom of the container.

A top-to-bottom box layout tries to make all of its container's components equally wide as wide as the largest preferred width. If the container is forced to be wider than that, then the box layout tries to make all the components as wide as the container. If the components aren't all the same width (due to restricted maximum size or to any of them having strict left or right alignment), then X alignment comes into play.

The X alignments affect not only the components' positions relative to each other, but also the location of the components (as a group) within their container. The following figures illustrate alignment of components that have restricted maximum widths.

In the first figure, all three components have an X alignment of 0.0 (

Box.createVerticalGlue()

8). This means that the components' left sides should be aligned. Furthermore, it means that all three components are positioned as far left in their container as possible.

In the second figure, all three components have an X alignment of 0.5 (

Box.createVerticalGlue()

9). This means that the components' centers should be aligned, and that the components should be positioned in the horizontal center of their container.

In the third figure, the components have an X alignment of 1.0 (

new Box.Filler(minSize, prefSize, maxSize)

0). You can guess what that means for the components' alignment and position relative to their container.

You might be wondering what happens when the components have both restricted maximum sizes and different X alignments. The next figure shows an example of this:

As you can see, the left side of the component with an X alignment of 0.0 (

Box.createVerticalGlue()

8. is aligned with the center of the component that has the 0.5 X alignment (

Box.createVerticalGlue()

9), which is aligned with the right side of the component that has an X alignment of 1.0 (

new Box.Filler(minSize, prefSize, maxSize)

0). Mixed alignments like this are further discussed in .

What if none of the components has a maximum width? Well, if all the components have identical X alignment, then all components are made as wide as their container. If the X alignments are different, then any component with an X alignment of 0.0 (left) or 1.0 (right) will be smaller. All components with an intermediate X alignment (such as center) will be as wide as their container. Here are two examples:

To get to know BoxLayout better, you can run your own experiments with BoxLayoutDemo.

-

Try this:

1. Compile and run BoxLayoutDemo. The source files are new Box.Filler(minSize, prefSize, maxSize) 4
   and new Box.Filler(minSize, prefSize, maxSize) 5
   . See Getting Started with Swing if you need help compiling or running this application. You'll see a window like the one above that contains three rectangles. Each rectangle is an instance of new Box.Filler(minSize, prefSize, maxSize) 6, which is a new Box.Filler(minSize, prefSize, maxSize) 7 subclass.
2. Click inside one of the rectangles. This is how you change the rectangle's X alignment.
3. Click the check box at the bottom of the window. This turns off restricted sizing for all the rectangles.
4. Make the window taller. This makes the rectangles' container larger than the sum of the rectangles' preferred sizes. The container is a new Box.Filler(minSize, prefSize, maxSize) 8 that has a red outline, so that you can tell where the container's edges are.

---

Using Invisible Components as Filler

Each component controlled by a box layout butts up against its neighboring components. If you want to have space between components, you can either add an empty border to one or both components, or insert invisible components to provide the space. You can create invisible components with the help of the

new Box.Filler(minSize, prefSize, maxSize)

9 class.

The

new Box.Filler(minSize, prefSize, maxSize)

9

class defines a nested class,

container.add(firstComponent); container.add(Box.createRigidArea(new Dimension(5,0))); container.add(secondComponent);

1

that provides invisible components. The

new Box.Filler(minSize, prefSize, maxSize)

9 class provides convenience methods to help you create common kinds of filler. The following table gives details about creating invisible components with

new Box.Filler(minSize, prefSize, maxSize)

9 and

container.add(firstComponent); container.add(Box.createRigidArea(new Dimension(5,0))); container.add(secondComponent);

1.

Type Size Constraints How to Create

Box.createRigidArea(size)

horizontal

Box.createHorizontalGlue()

vertical

Box.createVerticalGlue()

(as specified)

new Box.Filler(minSize, prefSize, maxSize)

Here's how you generally use each type of filler:

Rigid area Use this when you want a fixed-size space between two components. For example, to put 5 pixels between two components in a left-to-right box, you can use this code:

container.add(firstComponent); container.add(Box.createRigidArea(new Dimension(5,0))); container.add(secondComponent);

-

Note: The

new Box.Filler(minSize, prefSize, maxSize)

9 class provides another kind of filler for putting fixed space between components: a vertical or horizontal strut. Unfortunately, struts have unlimited maximum heights or widths (for horizontal and vertical struts, respectively). This means that if you use a horizontal box within a vertical box, for example, the horizontal box can sometimes become too tall. For this reason, we recommend that you use rigid areas instead of struts.

-

Glue

Use this to specify where excess space in a layout should go. Think of it as semi-wet glue -- stretchy and expandable, yet taking up no space unless you pull apart the components that it's sticking to. For example, by putting horizontal glue between two components in a left-to-right box, you make any extra space go between those components, instead of to the right of all the components. Here's an example of making the space in a left-to-right box go between two components, instead of to the right of the components:

container.add(firstComponent); container.add(Box.createHorizontalGlue()); container.add(secondComponent);

Custom

container.add(firstComponent); container.add(Box.createRigidArea(new Dimension(5,0))); container.add(secondComponent);

1

Use this to specify a component with whatever minimum, preferred, and maximum sizes you want. For example, to create some filler in a left-to-right layout that puts at least 5 pixels between two components and ensures that the container has a minimum height of 100 pixels, you could use this code:

container.add(firstComponent); Dimension minSize = new Dimension(5, 100); Dimension prefSize = new Dimension(5, 100); Dimension maxSize = new Dimension(Short.MAX_VALUE, 100); container.add(new Box.Filler(minSize, prefSize, maxSize)); container.add(secondComponent);

Fixing Alignment Problems

Two types of alignment problems sometimes occur with

Box.createRigidArea(size)

3:

A group of components all have the same alignment, but you want to change their alignment to make them look better. For example, instead of having the centers of a group of left-to-right buttons all in a line, you might want the bottoms of the buttons to be aligned. Here's an example:

Two or more components controlled by a

Box.createRigidArea(size) 3 have different default alignments, which causes them to be mis-aligned. For example, as the following shows, if a label and a panel are in a top-to-bottom box layout, the label's left edge is, by default, aligned with the center of the panel.

In general, all the components controlled by a top-to-bottom

Box.createRigidArea(size)

3 object should have the same X alignment. Similarly, all the components controlled by a left-to-right

container.add(firstComponent); container.add(Box.createHorizontalGlue()); container.add(secondComponent);

1 should generally have the same Y alignment. You can set a

new Box.Filler(minSize, prefSize, maxSize)

7's X alignment by invoking its

container.add(firstComponent); container.add(Box.createHorizontalGlue()); container.add(secondComponent);

3 method. An alternative available to all components is to override the

container.add(firstComponent); container.add(Box.createHorizontalGlue()); container.add(secondComponent);

4 method in a custom subclass of the component class. Similarly, you set the Y alignment of a component by invoking the

container.add(firstComponent); container.add(Box.createHorizontalGlue()); container.add(secondComponent);

5 method or by overriding

container.add(firstComponent); container.add(Box.createHorizontalGlue()); container.add(secondComponent);

6.

Here is an example, taken from , of changing the Y alignments of two buttons so that the buttons' bottoms are aligned:

button1.setAlignmentY(Component.BOTTOM_ALIGNMENT); button2.setAlignmentY(Component.BOTTOM_ALIGNMENT);

By default, most components have center X and Y alignment. However, buttons, combo boxes, labels, and menu items have a different default X alignment value:

container.add(firstComponent); container.add(Box.createHorizontalGlue()); container.add(secondComponent);

8. The previous picture shows what happens if you put a left-aligned component such as a label together with a center-aligned component in a container controlled by a top-to-bottom

Box.createRigidArea(size)

3.

The program gives examples of fixing mismatched alignment problems. Usually, it's as simple as making an offending button or label be center aligned. For example:

label.setAlignmentX(Component.CENTER_ALIGNMENT);

Specifying Component Sizes

As we mentioned before,

Box.createRigidArea(size)

3 pays attention to a component's requested minimum, preferred, and maximum sizes. While you're fine tuning the layout, you might need to adjust these sizes.

Sometimes the need to adjust the size is obvious. For example, a button's maximum size is generally the same as its preferred size. If you want the button to be drawn wider when additional space is available, then you need to change its maximum size.

Sometimes, however, the need to adjust size is not so obvious. You might be getting unexpected results with a box layout, and you might not know why. In this case, it's usually best to treat the problem as an first. If adjusting the alignments doesn't help, then you might have a size problem. We'll discuss this further a bit later.

-

Note: Although

Box.createRigidArea(size)

3 pays attention to a component's maximum size, most layout managers do not. For example, if you put a button in the south part of a

Box.createHorizontalGlue()

1, the button will probably be wider than its preferred width, no matter what the button's maximum size is.

Box.createRigidArea(size)

3, on the other hand, never makes a button wider than its maximum size.

-

You can change the minimum, preferred, and maximum sizes in two ways:

By invoking the appropriate container.add(firstComponent); Dimension minSize = new Dimension(5, 100); Dimension prefSize = new Dimension(5, 100); Dimension maxSize = new Dimension(Short.MAX_VALUE, 100); container.add(new Box.Filler(minSize, prefSize, maxSize)); container.add(secondComponent); 5 method (which is defined by the new Box.Filler(minSize, prefSize, maxSize) 7 class). For example:

Box.createRigidArea(size)

0

By overriding the appropriate

container.add(firstComponent); Dimension minSize = new Dimension(5, 100); Dimension prefSize = new Dimension(5, 100); Dimension maxSize = new Dimension(Short.MAX_VALUE, 100); container.add(new Box.Filler(minSize, prefSize, maxSize)); container.add(secondComponent); 7 method. For example: Box.createRigidArea(size)

1

If you're running into trouble with a box layout and you've ruled out alignment problems, then the trouble might well be size-related. For example, if the container controlled by the box layout is taking up too much space, then one or more of the components in the container probably needs to have its maximum size restricted.

Which layout arranges the components horizontally?

Summary of the layout managers.

How do I set layout in Swing?

You can install a new layout manager at any time by using the setLayout() method. For example, we can set the layout manager of a Swing container to a type called BorderLayout like so: myContainer . setLayout ( new BorderLayout () );

What is the difference between border layout and box layout?

In the top part of the GUI, a top-to-bottom box layout places a label above a scroll pane. In the bottom part of the GUI, a left-to-right box layout places two buttons next to each other. A BorderLayout combines the two parts of the GUI and ensures that any excess space is given to the scroll pane.

Which layout manager allows you to stack components on top of each other?

Basic Layout Managers
-----	---------------------
FlowLayout	Default for java.applet.Applet, java.awt.Panel and java.swing.JPanel. Places components sequentially (left to right) in the order they were added. You can specify the order.
CardLayout	Stacks components like a deck of cards

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