Step through the program
Stepping is the process of controlling step-by-step execution of the program.
IntelliJ IDEA provides a set of stepping actions, which are used depending on your strategy (for example, whether you need to go directly to the next line or enter the methods invoked on your way there).
The stepping buttons are located on the Debug tool window toolbar.
Step over
Steps over the current line of code and takes you to the next line even if the highlighted line has method calls in it. The implementation of the methods is skipped, and you move straight to the next line of the caller method.
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Click the Step over button
or press F8.
In the example, line 5 is about to be executed. If you step over, the debugger will move straight to line 6 without jumping into the doCount() method.
If there are breakpoints inside the skipped methods, the debugger will stop at them. To skip any breakpoints on the way, use Force step over.
Step into
Steps into the method to show what happens inside it. Use this option when you are not sure the method is returning a correct result.
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Click the Step into button
or press F7.
In the example, line 5 is about to be executed. If you step into, the debugger will jump into the implementation of the count(int to) method allowing you to examine in detail how its result is produced.
If there are several method calls on the line, IntelliJ IDEA asks you which method to enter. This feature is called Smart step into.
You can configure Smart Step Into to be automatically used every time when there are multiple method calls on the line. Alternatively, it can be invoked only when you expressly do so. To configure this feature, go to and set the Always do smart step into option as required.
Some methods (for example methods of standard Java classes like System) are skipped by Step into as you normally don't need to debug them. This list can be fine-tuned on the page of the Settings/Preferences dialog Ctrl+Alt+S.
Smart step into
Smart step into is helpful when there are several method calls on a line, and you want to be specific about which method to enter. This feature allows you to select the method call you are interested in.
From the main menu, select or press Shift+F7.
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Click the method or select it using the arrow keys and press Enter/F7.
You can configure Smart step into to be used instead of the regular Step into every time there are multiple method calls on the line. This is done in .
Step out
Steps out of the current method and takes you to the caller method.
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Click the Step out button
or press Shift+F8.
In the example, stepping out skips all iterations of the loop and takes you straight to themain method (the caller).
Run to cursor
Continues the execution until the position of the caret is reached.
Place the caret at the line where you want the program to pause.
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Click the Run to cursor button
or press Alt+F9.
Also, you can Run to Cursor with a single click. For this, click the line number in the gutter.
You can configure whether you want Run to Cursor to work on clicking a line number in .
In the example, Run to cursor will continue the execution and stop at line 7 as if there were a breakpoint. If there are breakpoints in the count() method, the program will be suspended there.
To skip any breakpoints on the way, use Force run to cursor.
Force step into
Steps in the method even if this method is skipped by the regular Step Into.
Click the Force step into button
or press Shift+Alt+F7.
In the example, the execution is suspended right before a line which is about to call System.out.println().
With Force Step Into, we jump right into the implementation of the System.out.println() method, while the regular Step Into would take us to line 20.
Force run to cursor
Continues the execution until the position of the caret is reached. All breakpoints on the way are ignored.
Place the caret at the line where you want the program to pause.
From the main menu, select or press Ctrl+Alt+F9.
In the example, Force run to cursor will continue the execution and stop at line 7 as if there were a breakpoint. The breakpoint inside count() will not have any effect.
Force step over
Steps over the current line of code and takes you to the next line even if the highlighted line has method calls in it. If there are breakpoints in the called methods, they are ignored.
From the main menu, select or press Shift+Alt+F8.
In the example, stepping over takes you to the print statement on line 6 even though there is a breakpoint in the count() method, which would otherwise suspend the application in all iterations of the loop.
Drop frame
Allows you to undo the last frame and restore the previous frame in the stack. This can be useful, for example, if you've mistakenly stepped too far, or want to re-enter a function where you missed a critical spot.
Note that this option only affects local variables and does not restore the overall program state in that it does not revert values for static and instance variables. This may result in an altered program flow.
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Click the Drop Frame button
.
In the example, dropping the frame returns you to the caller method as if count has never been executed.
There are no static or instance variables, which were affected, however the console output stays.
Improve stepping speed
Debugger features consume resources and may impact stepping performance. If the performance is not satisfactory, follow the recommendations provided in this chapter to optimize it.
Use the Overhead feature to identify the cause(s) of performance degradation.
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Disable or minimize the use of the following features if they are not required for your project:
- Method breakpoints and field watchpoints
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The Show method return values option
The Alternate view for Collections classes option ( )
'toString' object view ( )
Simplify the conditions for breakpoints and watchpoints, especially frequently hit ones.
During the debugging session, switch to a view with fewer elements.