Normally, breakpoints fire on each invocation. It is possible to configure breakpoints such that they fire when certain conditions are met.
- Go to the
execute()method of theSampleHandlerclass. - Clear any existing breakpoints by double-clicking them or using Delete all breakpoints from the Breakpoints view.
- Add a breakpoint to the first line of the
execute()method body. - Right-click on the breakpoint and select the Breakpoint Properties menu. (It can also be shown by Ctrl + double-clicking, or Cmd + double-clicking on OS X on the breakpoint icon itself.)
- Set the Hit Count field to
3, and click on OK. - Click on the Hello World icon button three times. On the third click, the debugger will open up at that line of code.
- Open the breakpoint properties, deselect Hit Count and select the Enabled and Conditional options. Put the following code into the conditional trigger field:
((org.eclipse.swt.widgets.Event)event.trigger).stateMask == 65536
- Click on the Hello World icon and the breakpoint will not fire.
- Hold down Alt, click on the Hello World icon, and the debugger will open. (
65536is the value ofSWT.MOD3, which is the Alt key.)
When a breakpoint is created, it is enabled by default. A breakpoint can be temporarily disabled, which has the effect of removing it from the flow of execution. Disabled breakpoints can be trivially re-enabled on a per-breakpoint basis, or from the Breakpoints view. Quite often it's useful to have a set of breakpoints defined in the codebase, but not necessarily have them all enabled at once.
It is also possible to temporarily disable all breakpoints using the Skip All Breakpoints setting, which can be changed from the corresponding item in the Run menu (when the debug perspective is enabled), or the corresponding icon 
in the Breakpoints view. When this is toggled, no breakpoints will be fired.
Conditional breakpoints must use a Boolean expression, rather than a statement or a set of statements. Sometimes this is constraining; if that's the case, having a utility class with a static method allows more complex code paths (with the caveat that all interesting data must be passed in as method arguments).