IntelliJ IDEA 2016.3 Help

Debugger Basics

In this section:

Debug

After you have configured a run configuration for your project, you can launch it in debug mode by pressing Shift+F9.

In the Debug tool window you can see the list of frames and threads with their states, variables and watches. When you select a frame, you see the variables corresponding to the selected frame.

Useful debugger shortcuts

Breakpoints

Breakpoint details and condition

If you want to change details of a breakpoint, press Ctrl+Shift+F8. Here you can specify the breakpoint conditions.

/help/img/idea/2016.3/breakpointProperties.png

And if you have any instance marked with a label, you can use it in the condition expression as well:

/help/img/idea/2016.3/breakpointProperties_label.png

To see all breakpoints in the project (with more advanced settings), press the same shortcut Ctrl+Shift+F8 again.

Field breakpoints

In addition to conditional breakpoints you can also use Field breakpoints. These breakpoints stop when a field is accessed for read or write. To create such a breakpoint, just click on the gutter at a field declaration:

/help/img/idea/2016.3/field_breakpoint1.png

Action breakpoints

Another action might be useful if you want to evaluate something at a particular line of code without actually making a stop. You can do that by using the Action breakpoint. To create one, just click on the gutter while holding Shift.

/help/img/idea/2016.3/action_breakpoint.png

Temporary breakpoints

To create a breakpoint that stops only once, click the left gutter while holding Shift+Alt.

/help/img/idea/2016.3/temporary_breakpoint.png

Refer to the section Types of Breakpoints for details.

Disable breakpoints

It's also useful to know that any breakpoint can be quickly disabled by clicking on the gutter while holding Alt.

/help/img/idea/2016.3/quick_disable_breakpoints.png

Refer to the section Enabling, Disabling and Removing Breakpoints for details.

Debugger session

Smart step into

Sometimes it happens that you stay at a line and want to step into a particular method but not the first one which will be invoked. In this case you can use Smart step into by pressing Shift+F7 to choose a particular method. This is a great time-saver.

/help/img/idea/2016.3/smart-step-into-pup-up-window-new.png

Refer to the section Choosing a Method to Step Into for details.

Drop frame

In case you want to “go back in time” while debugging you can do it via Drop Frame action. This is a great help if you mistakenly stepped too far. This will not revert the global state of your application but at least will get you back by stack of frames.

/help/img/idea/2016.3/drop_frame.png

The icon /help/img/idea/2016.3/frames_drop_frame.png is described in the Debug tool window reference.

Run to cursor

Sometimes you need to resume the program and stop at another line of code, without adding another break point. Easy: just press Alt+F9.

/help/img/idea/2016.3/run_to_cursor.png

The icon /help/img/idea/2016.3/frames_run_to_cursor.png is described in the toolbar reference of the Debug tool window.

Mark instance

If you want a particular instance to be always recognized while debugging, you can mark it with a colored label via F11 or the context menu in the Variables and Watches tabs.

/help/img/idea/2016.3/mark_object.png

The next time this instance appears in Watches, Variables or Evaluate expression, you will see the label:

/help/img/idea/2016.3/mark_object1.png

Evaluate expression

While in debug mode, you can evaluate any expression by pressing Alt+F8.

/help/img/idea/2016.3/evaluate_expression1.png

This tool provides code completion just as in the editor so it’s very easy to enter any expression:

/help/img/idea/2016.3/evaluate_expression2.png

If you have any instances marked with labels, code completion will offer you its names so you can evaluate them:

/help/img/idea/2016.3/evaluate_expression3.png

Refer to the section Evaluating Expressions for details.

Reload changes and hot swapping

Sometimes it happens that you need to insert minor changes in your code without shutting down the process. Since Java VM has such a feature as HotSwap, the IDE handles these cases automatically and offers you to reload the changed classes whenever you compile the changed classes while in debug mode.

Keep in mind that Java VM’s HotSwap has a number of constraints and does not support reloading of static fields and methods.

Remote debug

The final thing you definitely should know about debugging in IntelliJ IDEA is Remote debug. Remote debug means attaching debugger to a process which is already running on a specific port on your or any other’s host. This way you can attach the debugger to your application server which is running standalone.

To create a remote configuration, go to Edit configurations and add Remote run configuration. Make sure to specify the correct host and port before you run this configuration.

Settings

If you want to change the default debugger settings, choose Debugger in IntelliJ IDEA Settings.

See Also

Procedures:

External Links:

Last modified: 7 December 2016