Java切换策略FocusTraversalPolicy

Question

I have a question, does this chunk of code set the newPolicy to null when togglePolicy.isSelected() ?

if ("toggle".equals(e.getActionCommand())) {
        frame.setFocusTraversalPolicy(togglePolicy.isSelected() ?
                newPolicy : null);
    }
}

Answer 1

Nope, it sets frame focusTraversalPolicy to null when isSelected() is false (when it is not selected). if isSelected() was true it would set the newPolicy as the traversal policy.

you may want to take a look at here

Answer 2

I guess you stumbled upon the ternary operator . It works as follows:

<condition> ? <result if true> : <result if false>

In your case, you evaluate togglePolicy.isSelected() first. If the evaluation returns true , than you set the policy to newPolicy . Else the policy will be set to null .