Solving Common Layout Problems - Java Tutorial 5.0 英文版

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Solving Common Layout Problems

Problem: How do I specify a component's exact size?

• First, make sure that you really need to set the component's exact size. Each Swing component has a different preferred size, depending on the font it uses and the look and feel. For this reason, it often doesn't make sense to specify a Swing component's exact size.

• If the component isn't controlled by a layout manager, you can set its size by invoking the setSize or setBounds method on it. Otherwise, you need to provide size hints and then make sure you're using a layout manager that respects the size hints.

• If you extend a Swing component class, you can give size hints by overriding the component's getMinimumSize, getPreferredSize, and getMaximumSize methods. What's nice about this approach is that each getXxxxSize method can get the component's default size hints by invoking super.getXxxxSize(). Then it can adjust the size, if necessary, before returning it.

• Another way to give size hints is to invoke the component's setMinimumSize, setPreferredSize, and setMaximumSize methods.

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Note:  No matter how you specify your component's size, be sure that your component's container uses a layout manager that respects the requested size of the component. The FlowLayout and GridBagLayout managers use the component's preferred size (the latter depending on the constraints that you set), but BorderLayout and GridLayout usually don't. The BoxLayout manager generally uses a component's preferred size (although components can be larger), and is one of the few layout managers that respects the component's maximum size.

If you specify new size hints for a component that's already visible, you then need to invoke the revalidate method on it, to make sure that its containment hierarchy is laid out again. Then invoke the repaint method.

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Problem: My custom component is being sized too small.

• Does the component implement the getPreferredSize and getMinimumSize methods? If so, do they return the right values?
• Are you using a layout manager that can use as much space as is available? See Tips on Choosing a Layout Manager for some tips on choosing a layout manager and specifying that it use the maximum available space for a particular component.

If you don't see your problem in this list, see Solving Common Component Problems.

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