[[wikipedia:Debugger|Debugger]] is a program that helps to find out what other programs are doing.

[[wikipedia:Debugger|Debugger]] is a program that helps to find out what other programs are doing.

== Motto

== Motto ==

"Every sufficiently advanced technology is indistinguishable from magic" ... until you debug it.

"Every sufficiently advanced technology is indistinguishable from magic" ... until you debug it.

== Plot

== Plot ==

Often people use debugger to understand why their own code does not do, what they would like it to do. However debugger is incredibly useful for other purposes as well. Here is its story.

Often people use debugger to understand why their own code does not do, what they would like it to do. However debugger is incredibly useful for other purposes as well. Here is its story.

[[wikipedia:Debugger|Debugger]] is a program that helps to find out what other programs are doing. Often people use debugger to understand why their own code does not do, what they would like it to do. However debugger is incredibly useful for other purposes as well. Here is its story.

[[wikipedia:Debugger|Debugger]] is a program that helps to find out what other programs are doing.

 

 

 

 

Often people use debugger to understand why their own code does not do, what they would like it to do. However debugger is incredibly useful for other purposes as well. Here is its story.

== Building [[Modular system]]s ==

== Building [[Modular system]]s ==

== Knowing Every Detail ==

== Knowing Every Detail ==

Once a customer of the [[NetBeans Platform]] invited me for a consultation. It is not common to send the creator of a framework for a consultation, the usual strategy is to send the junior guy to find out if they can spell [[Java]]. Later send somebody more experienced and only if every effort fails, ask the guru. But even for me, as a creator of the [[NetBeans Platform]], it is important to see real customer from time to time, so I took the opportunity to visit such important customer.

Once a customer of the [[NetBeans Platform]] invited me for a consultation. It is not common to send the creator of a framework for a consultation, the usual strategy is to send the junior guy to find out if they can spell [[Java]]. Later send somebody more experienced and only if every effort fails, ask the guru. But even for me, as a creator of the [[NetBeans Platform]], it is important to see real customer from time to time, so I took the opportunity to visit such an important customer.

Certainly I can talk about architecture decisions and explain how to use [[NetBeans]] [[API]]s on a higher level, but when it comes to details, I may often be in total [[cluelessness]] situation (there is a lot of [[NetBeans]] [[API]]s check at http://bits.netbeans.org/7.3/javadoc/ and we design them as a team). As a result my most common answer to customer questions was: ''I don't know. Let's put a breakpoint somewhere''!

Certainly I can talk about architecture decisions and explain how to use [[NetBeans]] [[API]]s on a higher level, but when it comes to details, I may often be in total [[cluelessness]] situation (there is a lot of [[NetBeans]] [[API]]s check at http://bits.netbeans.org/7.3/javadoc/ and we design them as a team). As a result my most common answer to customer questions was: ''I don't know. Let's put a breakpoint somewhere''!

[[Debugger]] can be useful even for understanding a system without a source code. It is just essential to know where to place a breakpoint. Once I was trying to understand the behavior of [[iOS]]'s '''WebUI''' - of course its not open source, but luckily [[Gdb]] (as well as many other [[debugger]]s) can place a breakpoint to a method and stop the execution when the method is called. As we needed to find out why the '''WebUI''' does not load a resource using our [[URL]],

[[Debugger]] can be useful even for understanding a system without a source code. It is just essential to know where to place a breakpoint. Once I was trying to understand the behavior of [[iOS]]'s '''WebUI''' - of course its not open source, but luckily [[Gdb]] (as well as many other [[debugger]]s) can place a breakpoint to a method and stop the execution when the method is called. As we needed to find out why the '''WebUI''' does not load a resource using our [[URL]],

we added a breakpoint to constructor of '''NURL'''. As soon as the breakpoint was hit, we could inspect the stack, see names of methods and even values of registers. Based on that we could get a clue of what was going on.

we added a breakpoint to constructor of '''NSURL'''. As soon as the breakpoint was hit, we could inspect the stack, see names of methods and even values of registers. Based on that we could get a clue of what was going on.

Once I was inspecting a closed source [[Java]] implementation of a [[Mylyn]] connector [[API]]. The system had three layers: User interface and connector [[API]] was [[open source]], the library in middle was not. By placing breakpoints into the bottom connector [[API]] I obtained very [[good]] understanding of what the blackbox in middle does. It is all about knowing where to place the breakpoints.

Once I was inspecting a closed source [[Java]] implementation of a [[Mylyn]] connector [[API]]. The system had three layers: User interface and connector [[API]] was [[open source]], the library in middle was not. By placing breakpoints into the bottom connector [[API]] I obtained very [[good]] understanding of what the blackbox in middle does. It is all about knowing where to place the breakpoints.

[[Image:DebugMavenBuild.png|thumb|right]]

[[Image:DebugMavenBuild.png|thumb|right]]

Do you know the difference between [[Ant]] and [[Maven]]? In [[Ant]] you described what to do and make calls to individual [[Ant]] tasks. On the other hand in [[Maven]] you describe what should be done and let the system do it for you. That is more [[Declarative Programming|declarative]], but also more [[framework]] like: often it is hard to find out why some actions are not performed the way you'd like them to be.

Do you know the difference between [[Ant]] and [[Maven]]? In [[Ant]] you describe what to do and make calls to individual [[Ant]] tasks. On the other hand in [[Maven]] you describe what should be done and let the system do it for you. That is more [[Declarative Programming|declarative]], but also more [[framework]] like: often it is hard to find out why some actions are not performed the way you'd like them to be.

Recently we were writing a [[Maven]] plugin in [[Ant]] (yes, that is possible, both projects are supported by [[Apache]] foundation and as such they seek some synergy). Documentation how to achieve this is available, however it covers only the most common [[usecase]]s. When you need to take it to extreme, use not only simple [[Ant]] script, but rather a set of files that work in [[harmony]], you need to understand what is happening. The only way to do it is to use [[debugger]]. Can you debug your build?

Recently we were writing a [[Maven]] plugin in [[Ant]] (yes, that is possible, both projects are supported by [[Apache]] foundation and as such they seek some synergy). Documentation how to achieve this is available, however it covers only the most common [[usecase]]s. When you need to take it to extreme, use not only simple [[Ant]] script, but rather a set of files that work in [[harmony]], you need to understand what is happening. The only way to do it is to use [[debugger]]. Can you debug your build?

Have your [[Java]] application exited without a reason? Try to place breakpoint to {{JDK|java/lang|System}}.exit(). If that does not work, create an ''exception'' breakpoint to stop when an exception is thrown.

Have your [[Java]] application exited without a reason? Try to place breakpoint to {{JDK|java/lang|System}}.exit(). If that does not work, create an ''exception'' breakpoint to stop when an exception is thrown.

Trying to influence behavior of your application with a system property and it does not work? Place a conditional breakpoint to {JDK|java/util|Properties}}.getProperty(name) to stop when ''name'' is equal to name of your property.

Trying to influence behavior of your application with a system property and it does not work? Place a conditional breakpoint to {{JDK|java/util|Properties}}.getProperty(name) to stop when ''name'' is equal to name of your property.

Curious to know why a communication to a [[HTTP]] server fails? Place a breakpoint to {{JDK|java/net|URL}} constructor. Etc.

Curious to know why a communication to a [[HTTP]] server fails? Place a breakpoint to {{JDK|java/net|URL}} constructor. Etc.

Once I was inspecting a closed source [[Java]] implementation of a [[Mylyn]] connector [[API]]. The system had three layers: User interface and connector [[API]] was [[open source]], the library in middle was not. By placing breakpoints into the bottom connector [[API]] I obtained very [[good]] understanding of what the blackbox in middle does. It is all about knowing where to place the breakpoints.

Once I was inspecting a closed source [[Java]] implementation of a [[Mylyn]] connector [[API]]. The system had three layers: User interface and connector [[API]] was [[open source]], the library in middle was not. By placing breakpoints into the bottom connector [[API]] I obtained very [[good]] understanding of what the blackbox in middle does. It is all about knowing where to place the breakpoints.

Have your [[Java]] application exited without reason? Try to place breakpoint to {{JDK|java/lang|System}}.exit(). If that does not work, create an ''exception'' breakpoint to stop when an exception is thrown.

Have your [[Java]] application exited without a reason? Try to place breakpoint to {{JDK|java/lang|System}}.exit(). If that does not work, create an ''exception'' breakpoint to stop when an exception is thrown.

Trying to influence behavior of your application with a system property and it does not work? Place a conditional breakpoint to {JDK|java/util|Properties}}.getProperty(name) to stop when ''name'' is equal to name of your property.

Trying to influence behavior of your application with a system property and it does not work? Place a conditional breakpoint to {JDK|java/util|Properties}}.getProperty(name) to stop when ''name'' is equal to name of your property.

we added a breakpoint to constructor of '''NURL'''. As soon as the breakpoint was hit, we could inspect the stack, see names of methods and even values of registers. Based on that we could get a clue of what was going on.

we added a breakpoint to constructor of '''NURL'''. As soon as the breakpoint was hit, we could inspect the stack, see names of methods and even values of registers. Based on that we could get a clue of what was going on.

Once I was inspecting a closed source [[Java]] implementation of a [[Mylyn]] connector [[API]]. The system had three layers: User interface and connector [[API]] was [[open source]], the library in middle was not. By placing breakpoints into the bottom connector [[API]] one can get very good understanding of what the blackbox in middle does. It is all about knowing where to place a breakpoint.

Once I was inspecting a closed source [[Java]] implementation of a [[Mylyn]] connector [[API]]. The system had three layers: User interface and connector [[API]] was [[open source]], the library in middle was not. By placing breakpoints into the bottom connector [[API]] I obtained very [[good]] understanding of what the blackbox in middle does. It is all about knowing where to place the breakpoints.

Have your [[Java]] application exited without reason? Try to place breakpoint to {{JDK|java/lang|System}}.exit(). If that does not work, create an ''exception'' breakpoint to stop when an exception is thrown.

Have your [[Java]] application exited without reason? Try to place breakpoint to {{JDK|java/lang|System}}.exit(). If that does not work, create an ''exception'' breakpoint to stop when an exception is thrown.

we added a breakpoint to constructor of '''NURL'''. As soon as the breakpoint was hit, we could inspect the stack, see names of methods and even values of registers. Based on that we could get a clue of what was going on.

we added a breakpoint to constructor of '''NURL'''. As soon as the breakpoint was hit, we could inspect the stack, see names of methods and even values of registers. Based on that we could get a clue of what was going on.

Once I was inspecting a closed source [[Java]] implementation of a [[Mylyn]] connector [[API]]. The system had three layers: User interface and connector [[API]] was [[open source]], in library in middle was not. By placing breakpoints into the bottom connector [[API]] one can get very good understanding of what the blackbox in middle does. It is all about knowing where to place a breakpoint.

Once I was inspecting a closed source [[Java]] implementation of a [[Mylyn]] connector [[API]]. The system had three layers: User interface and connector [[API]] was [[open source]], the library in middle was not. By placing breakpoints into the bottom connector [[API]] one can get very good understanding of what the blackbox in middle does. It is all about knowing where to place a breakpoint.

Have your [[Java]] application exited without reason? Try to place breakpoint to {{JDK|java/lang|System}}.exit(). If that does not work, create an ''exception'' breakpoint to stop when an exception is thrown.

Have your [[Java]] application exited without reason? Try to place breakpoint to {{JDK|java/lang|System}}.exit(). If that does not work, create an ''exception'' breakpoint to stop when an exception is thrown.

=== Debugging without Source Code ===

=== Debugging without Source Code ===

[[Debugger]] can be useful even for understanding a system without a source code. It is just essential to know where to place a breakpoint. Once I was trying to understand the behavior of [[iOS]]'s '''WebUI''' - of course its not open source, but luckily [[Gdb]] (as well as many other [[debugger]]s) can place a breakpoint to a method. As we needed to find out why the '''WebUI''' does not load a resource using our [[URL]],

[[Debugger]] can be useful even for understanding a system without a source code. It is just essential to know where to place a breakpoint. Once I was trying to understand the behavior of [[iOS]]'s '''WebUI''' - of course its not open source, but luckily [[Gdb]] (as well as many other [[debugger]]s) can place a breakpoint to a method and stop the execution when the method is called. As we needed to find out why the '''WebUI''' does not load a resource using our [[URL]],

we added a breakpoint to constructor of '''NURL'''. As soon as the breakpoint was hit, we could inspect the stack, see names of methods and even values of registers. Based on that we could get a clue of what was going on.

we added a breakpoint to constructor of '''NURL'''. As soon as the breakpoint was hit, we could inspect the stack, see names of methods and even values of registers. Based on that we could get a clue of what was going on.