Breakpoints are special markers that suspend program execution at a specific point. This lets you examine the program state and behavior. Breakpoints can be simple (for example, suspending the program on reaching some line of code) or involve more complex logic (checking against additional conditions, writing log messages, and so on).
Once set, a breakpoint remains in your project until you remove it explicitly, except for temporary breakpoints).
Types of breakpoints
The following types of breakpoints are available in IntelliJ IDEA:
Line breakpoints: suspend the program upon reaching the line of code where the breakpoint was set. This type of breakpoints can be set on any executable line of code.
Method breakpoints: suspend the program upon entering or exiting the specified method or one of its implementations, allowing you to check the method's entry/exit conditions.
Field watchpoints: suspend the program when the specified field is read or written to. This allows you to react to interactions with specific instance variables. For example, if at the end of a complicated process you are ending up with an obviously wrong value on one of your fields, setting a field watchpoint may help determine the origin of the fault.
Exception breakpoints: suspend the program when
Throwableor its subclasses are thrown. They apply globally to the exception condition and do not require a particular source code reference.
Set line breakpoints
Click the gutter at the executable line of code where you want to set the breakpoint. Alternatively, place the caret at the line and press Ctrl+F8.
If the line contains a lambda expression, you can select whether you want to set a regular line breakpoint, or the program should only be suspended when the lambda is called.
Set method breakpoints
Click the gutter at the line where the method is declared. Alternatively, place the caret at the line and press Ctrl+F8.
To suspend the program when the default constructor of some class is called, click the gutter at the line where the class is declared or place the caret at the line and press Ctrl+F8.
To match multiple classes or methods, click View Breakpoints in the left part of the Debug tool window, then click Add Alt+Insert and specify the class and method. Use
*to match the beginning, the ending, or the entire identifier.
print()methods in all classes (with any parameter list)
any method in the
all setters in the
Set field watchpoints
Click the gutter at the line where the field is declared. Alternatively, place the caret at the line and press Ctrl+F8.
Set exception breakpoints
Click View Breakpoints in the left part of the Debug tool window or press Ctrl+Shift+F8.
Depending on the type of the exception:
If you want to suspend the program when any instance of
Throwableis thrown, check Any Exception under Java Exceptions.
If you want to suspend the program when a specific exception or its subclasses are thrown, click Add Alt+Insert in the top-left corner of the dialog and enter the name of the exception.
For non-exception breakpoints: click the breakpoint in the gutter.
For all breakpoints: from the main menu, select Remove Delete.Ctrl+Shift+F8, select the breakpoint, and click
To avoid accidentally removing a breakpoint and losing its parameters, you can choose to remove breakpoints by dragging them to the editor or clicking the middle mouse button. To do this, go to Drag to the editor or click with middle mouse button. Clicking a breakpoint will then enable or disable it.and select
If you don't need to stop at your breakpoints for some time, you can mute them. This allows you to resume normal program operation without leaving the debugger session. After that, you can unmute breakpoints and continue debugging.
Click the Mute Breakpoints button in the toolbar of the Debug tool window.
When you remove a breakpoint, its internal configuration is lost. To temporarily turn an individual breakpoint off without losing its parameters, you can disable it:
For non-exception breakpoints: right-click it and set the Enabled option as required. You can also toggle them with the middle mouse button if removing breakpoints is not assigned to it.
For all breakpoints: click View Breakpoints Ctrl+Shift+F8 and check/uncheck the breakpoint on the list.
To move a breakpoint, drag it to another line.
To copy a breakpoint, hold Ctrl and drag a breakpoint to another line. This creates a breakpoint with the same parameters at the destination.
Configure breakpoints' properties
Depending on the breakpoint type, you can configure additional properties which allow you to tailor its operation for specific needs. The most used options are available via intentions.
To access breakpoint intentions, place the caret at the line with the breakpoint and press Alt+Enter. Use this option when you need to quickly configure basic breakpoint properties.
To access the full list of properties, right-click the breakpoint and click More or press Ctrl+Shift+F8. Use this option for a bird's eye view of all breakpoints and full control over their configuration.
Removes the breakpoint at the selected line.
Disables the breakpoint at the selected line.
Opens a dialog with the most used breakpoint properties. For more properties, click More or press Ctrl+Shift+F8.
|Stop only in the class|
Applies a class filter to exclude all descendants of the currently executed class.
|Do not stop in the class|
Applies a class filter to exclude the currently executed class.
|Stop only in the current object|
Applies an instance filter to exclude all instances except for the one that is currently executed. This action is only available in nonstatic context.
|Stop only if called from|
Applies a caller filter to exclude all methods except for the one corresponding to the previous frame in the stack.
|Do not stop if called from|
Applies a caller filter to exclude the method corresponding to the previous frame in the stack.
Clear the checkbox to temporarily disable a breakpoint without removing it from the project. Disabled breakpoints are skipped during stepping.
You can configure IntelliJ IDEA to enable/disable breakpoints on clicking rather than removing them altogether. To do this, go to Remove breakpoint option to Drag to the editor or click with middle mouse button.and set the
Specifies whether to pause the program execution when the breakpoint is hit.
Non-suspending breakpoints are useful when you need to log some expression without pausing the program (for example, when you need to know how many times a method was called) or if you need to create a master breakpoint that will enable dependent breakpoints when hit.
The following policies are available for the breakpoints that suspend program execution:
All: all threads are suspended when any of the threads hits the breakpoint.
Thread: only the thread which hits the breakpoint is suspended.
This option is used to specify a condition that is checked each time the breakpoint is hit. If the condition evaluates to
true, the selected actions are performed. Otherwise, the breakpoint is ignored.
The result of the expression is taken from the return statement. When there is no return statement, the result is taken from the last line of code.
In the body of the condition, you can use:
Multiple statements, including declarations, loops, anonymous classes, and so on
this(in nonstatic context), for example, to refer to the current exception:
!(this instanceof IOException)
Labels to include tracked instances in your expressions or check their boolean fields:
When evaluating expressions, make sure you are aware of their possible side effects as they may potentially affect the behavior and/or the result of the program.
When a breakpoint is hit, the following can be logged to the console:
"Breakpoint hit" message: a log message like
Breakpoint reached at ocean.Whale.main(Whale.java:5)
Stack trace: the stack trace for the current frame. This is useful if you want to check what paths have led to this point without interrupting the program execution.
Evaluate and log: the result of an arbitrary expression, for example,
users.size(). The expression disregards any access modifiers and is evaluated in the context of the line where the breakpoint is set.
The result of the expression is taken from the return statement. When there is no return statement, the result is taken from the last line of code which doesn't even have to be an expression: a literal works too. This can be used to produce a custom message or to keep track of some values as the program executes.
When evaluating expressions, make sure you are aware of their possible side effects as they may potentially affect the behavior and/or the result of the program.
Remove once hit
Specifies whether the breakpoint should be removed from the project after it has been hit once.
Disable until hitting the following breakpoint
When a breakpoint is selected in the Disable until hitting the following breakpoint box, it acts as a trigger for the current breakpoint. This disables the current breakpoint until the specified breakpoint has been hit.
You can also choose whether to disable it again after this has happened or leave it enabled.
This option is useful when you only need to suspend the program under certain conditions or after certain actions. In this case, the trigger breakpoint usually isn't required to stop the program execution and is made non-suspending.
IntelliJ IDEA debugger enables you to fine-tune the breakpoint operation by filtering out classes, instances, and caller methods and only suspend the program where needed.
The following types of filters are available:
Catch class filters: allow you to only suspend the program when the exception is going to be caught in one of the specified classes. Available only for exception breakpoints.
Instance filters: limit the breakpoint operation to particular object instances. This type of filter only takes effect in nonstatic context.
Class filters: limit the breakpoint operation to particular classes.
Caller filters: limit the breakpoint operation depending on the caller of the current method. Select if you need to stop at a breakpoint only when the current method is called (or not called) from a certain method.
To set up a filter, you can click the button near the text field and use a dialog or define it in text format. For text format, use the following syntax:
Classes and methods are specified using fully qualified names. If a filter is specified through a class name, it points at the class itself and all its subclasses which use its members via inheritance.
You can use patterns with the
*wildcard to define groups of classes or methods. A filter specified through a pattern points at classes/methods whose fully qualified names match this pattern.
Object instances are specified using instance IDs. You can find the object ID in the Variables tab when the object is in the scope or using the Memory tab.
Class names, caller methods, patterns, and instance IDs are separated with spaces.
To exclude a class or a caller method, type
-before its name.
In caller filters, use descriptors for parameters and return types, for example:
mypackage.MyObject.addString(Ljava/lang/String;)V. For detailed information on descriptors, refer to the official Oracle documentation.
A class/catch class filter that ignores the code inside the
A caller filter to exclude calls from
A class/catch class filter that applies the breakpoint to code in
Specifies if the breakpoint should work only after it has been hit a certain number of times. This is useful for debugging loops or methods, which are called several times.
After the count has completed, it is reset and starts anew. This means that if Pass count is set to
10, the breakpoint will work every tenth time it is hit.
If both Pass Count and Condition are set, IntelliJ IDEA first satisfies the condition and then checks for Pass Count.
Select to make the watchpoint work when the field is being read.
Select to make the watchpoint work when the field is being written to.
When this option is enabled, IntelliJ IDEA sets a combination of line breakpoints at the first and last statements of a method instead of using a slower "true" method breakpoint. Emulated method breakpoints improve debugging performance and thus are used by default.
We only recommend disabling this option if you are debugging remote code, or if you need to set a breakpoint at native methods or classes without line number information.
Select to make the breakpoint work each time the method or its descendants are entered.
Select to make the breakpoint work each time the method or its descendants are exited.
Select to make the breakpoint work when the specified exception was caught.
Select to make the breakpoint work when the specified exception was not caught. This allows you to examine the program state and detect the cause before the program crashes due to unhandled exception.
Breakpoints can have the following statuses:
After you have started a debugger session, the debugger checks whether it is technically possible to suspend the program at the breakpoint. If yes, the debugger marks the breakpoint as verified.
If it is technically possible to suspend the program at the breakpoint, however there are issues related to it, the debugger gives you a warning. This may happen, for example, when it is impossible to suspend the program at one of the method's implementations.
If it is technically impossible to suspend the program at the breakpoint, the debugger marks it as invalid. The most common cause for this is that there is no executable code on the line.
A breakpoint is marked as inactive/dependent when it is configured to be disabled until another breakpoint is hit, and this has not happened yet.
All breakpoints are temporarily inactive because they have been muted.
This breakpoint is temporarily inactive because it has been disabled.
The suspend policy is set for this breakpoint so that it does not suspend the execution when hit.
- Use breakpoints for "printf" debugging
- Use non-suspending logging breakpoints (sometimes referred to as watchpoints in other debuggers) instead of inserting print statements in your code. This provides a more flexible and centralized way of handling debug log messages.
- Set logging breakpoints more quickly
- To set a non-suspending logging breakpoint, hold Shift and click the gutter. This will not suspend the program execution and instead log a message like
Breakpoint reached at ocean.Whale.main(Whale.java:5). If you want to log some expression that is in front of you in the editor, select it before holding Shift and clicking the gutter.
- Add breakpoint descriptions
- If you have many breakpoints in your project, you can add descriptions to breakpoints for ease of search. To do this, right-click a breakpoint in the Breakpoints dialog Ctrl+Shift+F8 and select Edit description from the menu. Now when you start typing the breakpoint name, it gets the focus.
- Group breakpoints
- You can organize breakpoints into groups, for example, if you need to mark out breakpoints for a specific problem. To do this, in the Breakpoints dialog Ctrl+Shift+F8, select a breakpoint you want to place in a group and select from the menu.
- Lambda expressions vs. method references
- Due to JVM design, method references don't provide meaningful information in stack traces, as opposed to lambda expressions. Moreover, it is impossible to set a breakpoint on a method reference. If a method reference reduces traceability where it is critical, consider using lambda instead.
- Diagnose the cause of fatal errors
- As exception breakpoints work with
Throwable, you can also use them to suspend the program when a subclass of
Erroris thrown. This is useful for investigating the causes of errors like
StackOverflowError. With an exception breakpoint set up for them, you will be able to look into what happened in the program before it crashes.
- Test your program for concurrency issues
- A good way to find out if a multi-threaded program is robust in terms of concurrency is to use breakpoints that only suspend one thread when hit. Stopping a single thread may reveal problems in the design of the application, which would not otherwise be evident.