Solving Common Layout Problems
Note: This lesson covers writing layout code by hand, which can be challenging. If you are not interested in learning all the details of layout management, you might prefer to use the
GroupLayoutlayout manager combined with a builder tool to lay out your GUI. One such builder tool is the NetBeans IDE. Otherwise, if you want to code by hand and do not want to use
GridBagLayoutis recommended as the next most flexible and powerful layout manager.
If you are interested in using JavaFX to create your GUI, see Working With Layouts in JavaFX .
Problem: How do I specify a component's exact size?
- A handful of the more modern layout managers provide ways to override the size set by the component. Check whether the layout manager you are using allows you to specify component sizes.
- 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 does not make sense to specify a Swing component's exact size.
- If the component is not controlled by a layout manager, you can set its size by invoking the
setBoundsmethod on it. Otherwise, you need to provide size hints and then make sure you are 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
getMaximumSizemethods. What is nice about this approach is that each
getXxxxSizemethod can get the component's default size hints by invoking
super.getXxxxSize(). Then it can adjust the size, if necessary, before returning it. This is particularly handy for text components, where you might want to fix the width, but have the height determined from the content. However, sometimes problems can be encountered with
GridBagLayoutand text fields, wherein if the size of the container is smaller than the preferred size, the minimum size gets used, which can cause text fields to shrink quite substantially.
- Another way to give size hints is to invoke the component's
- If you specify new size hints for a component that is already visible, you then need to invoke the
revalidatemethod on it, to make sure that its containment hierarchy is laid out again. Then invoke the
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
GridBagLayoutmanagers use the component's preferred size (the latter depending on the constraints that you set), but
GridLayoutusually do not. The
BoxLayoutmanager 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.
Problem: My component does not appear after I have added it to the container.
- You need to invoke
repaintafter adding a component before it will show up in your container.
Problem: My custom component is being sized too small.
- Does the component implement the
getMinimumSizemethods? 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 do not see your problem in this list, see Solving Common Component Problems.