Debugger & Profiler In Netbeans

DEBUGGER & PROFILER IN NETBEANS 6.0 HANDS-ON DEMO

Using the debugger: Debugging is the process of examining your application for (runtime) errors. The process of debugging is accomplished by setting breakpoints and watches in your code and running it in the debugger. This enables you to execute your code line by line and have a closer look at the state of your application (values of variables, call order, etc.) in order to discover any problems. STEP 1: Write a simple application • •

Create a new Java Application Under the main method, write the following code: int sum = 0; for (int i=0; i<100000; i++) { sum = add(sum, square(i)); } System.out.println("Sum is " + sum);

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Under the Main class, add the following methods: private static int square(int x)

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return x*x; } private static int add(int a, int b) { return a+b; }

STEP 2: Set a breakpoint at the main method A breakpoint is a flag in the source code that tells the debugger where to stop execution of the program. When your program stops on a breakpoint, you can perform actions like examining the value of variables and single-stepping through your program. To set a breakpoint, Click in the left margin next to the line in the source code or put the insertion point in the line and press Ctrl-F8. STEP 3: Run the debugger by pressing Ctrl-F5 STEP 4: Step through your program Once execution of your program is halted, you can step through your lines of code using the following commands on the Debug menu or toolbar: • •

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Step Over (F8). Executes one source line. If the source line contains a call, executes the entire routine without stepping through the individual instructions. Step Over Expression (Shift-F8). Executes one method call in an expression. If an expression has multiple method calls, you can use Step Over Expression to step through an expression and view the value of each method call in the expression in the Local Variables window. Each time you use the Step Over Expression command, the debugger advances to the next method call in the expression and the completed method call is underlined. Step Over Expression behaves like Step Over when there are no additional method calls. Step Into (F7). Executes one source line. If the source line contains a call, the IDE stops just before executing the first statement of the routine. You can also start a debugging session with the Step Into command. Program execution stops on the first line after the main routine before any changes have been made to the state of the program. Step Out (Ctrl-F7). Executes one source line. If the source line is part of a routine, executes the remaining lines of the routine and returns control to the caller of the routine. The completed method call is highlighted in the Source Editor.

STEP 5: View program information To view variables and expressions, either: • • •

Use the local variables window Or move your mouse over the variable Or create a watch o Select the variable or expression in the Source Editor, right-click, and choose New Watch (Ctrl-Shift-F7). The New Watch dialog box opens with the variable or expression entered in the text field. o Click OK. The Watches window opens with the new watch selected.

EXTRA TASK: Use the call stack The Call Stack window lists the sequence of calls made during the execution of the current thread. By default, the Call Stack window opens automatically whenever you start a debugging session. To view the call stack (in case you don’t see it), choose menu Window – Debugging – Call Stack or press Alt + Shift + 3

Using the profiler Profiling is the process of examining an application in order to locate memory or performancerelated issues. When profiling a Java application, you can monitor the Java Virtual Machine (JVM) and obtain data about application performance, including method timing, object allocation and garbage collection. You can use this data to locate potential areas in your code that can be optimized to improve performance. TO DO: Add the following code into the for loop above:

int sum = 0; for (int i=0; i<100000; i++) { sum = add(sum, square(i)); Date date = new Date(); } System.out.println("Sum is " + sum);

(Remember to fix imports errors before you continue)

TASK 1: Monitor the execution time (CPU Performance)

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Choose menu Profile – Profile Main Project You might be asked to do some configuration for the first time of profiling

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Select CPU Tab

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Choose Entire Application

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Under Filter, select Profile only project classes

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Click Run

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When asked, click Yes to view the snapshot

A snapshot is a profiling data at a specific point of time. It can be reused for comparison purpose.

The result snapshot of CPU Profiling shows you the execution time of each methods and their number of invocations

From the snapshot of the example here, you can see that the main method itself takes a lot of time compared to the other two methods add and square. It’s totally up to you to justify whether it is a reasonable result. Also notice from the snapshot that both add and square methods are called 100000 times.

TASK 2: Monitor the memory usage

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Choose menu Profile – Profile Main Project You might be asked to do some configuration for the first time of profiling

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Select Memory Tab

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Choose Record object creation only

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Click Run

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When asked, click Yes to view the snapshot

Notice that 100000 objects of type Date has been created and they account for roughly 251832 Bytes in memory. This is because of the line we’ve recently added. We keep creating new object of type Date without disposing it. This is one trivial cause of memory leak issues.

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