Heavy Fog - Layout Managers and the word "preferred"

Question

Hello again world.
While reading the API, the tutorials, and various other documentation dealing with layout managers, I keep coming across the word "preferred" - "preferred size", "preferred width", "preferred height", and so on.
However, I can't seem to visualize just what "preferred" means in this context.
Do they pre-suppose that one has used the setPreferredSize() method?
And if no set*Size() method is used, how does the parent container size its components? The literature just comes back to "preferred" this and that.
This whole "preferred" business is, to me, circular and confusing, and the more I read, the foggier things get.
Anyone out there with a fresh breeze?
Thank you one and all.
Ciao for now.

Answer 1

You should never use setSize(). The size of a component is set by the LayoutManager as the components in the container are layed out. For example say you are using a GridLayout and you have 3 buttons: following text:
small = new JButton("small");
medium = new JButton("medium sized");
large = new JButton("the largest button");
The preferred size of each button is calculated to be:
a) the size of the text +
b) the border +
c) the margin
When components are added to the GridLayout all components are made the same size. The preferredSize does not change, but the size of each button is set the the largest preferredSize of the three buttons before it is painted. The GridLayout ignores the preferredSize of individual components and only cares about the largest component.
On the other hand the FlowLayout repects the preferredSize of each component when they are layed out and painted. When using a FlowLayout you can set the preferredSize of each component to be the same by doing the following:
small.setPreferredSize( large.getPreferredSize() );
medium.setPreferredSize( large.getPreferredSize() );
Every LayoutManager has rules it follows with respect to preferredSize, minimumSize and maximumSize. Read the Swing tutorial on [url http://java.sun.com/docs/books/tutorial/uiswing/layout/visual.html]Using Layout Managers.