Eclipse: Use Memory Analyzer (MAT) - Here's how
Related Videos: CppCon 2017: Matt Godbolt “What Has My Compiler Done for Me Lately? Unbolting the Compiler's Lid” (May 2024).
As you know, Java programs need a lot of RAM. The Eclipse Memory Analyzer, which detects memory leaks and presents the results graphically, can help.
Set up the Eclipse Memory Analyzer
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This self-made Java program was used for testing for the Eclipse Memory Analyzer. It is an endless loop where an entry is added to the list each time the loop is run.
It is best to create a separate folder for the heap dump file and enter it under Working Directory> Other.
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MAT is not available under Eclipse by default, so you would still need to install it to use it.
- Since MAT is also available as a plugin, you can integrate it under Eclipse and start it from there. To do this, click Help> Eclipse Marketplace and enter the term MAT in the search field. You then only need to click the Install button in the list of search results.
- Then you can either start an existing Java project in Eclipse or create a new one and assign appropriate parameters to it. While the program is running, MAT creates several files, which is why it is recommended to create a subfolder in the project so that MAT stores the files there. You create the subfolder by selecting the project folder and clicking New> Folder via the context menu of the mouse.
- Use the mouse to mark the Java file that contains the main method. Under Run> Run Configurations, click on J ava Application> Start on the left and enter the following parameters in the VM Arguments field: -XX: + HeapDumpOnOutOfMemoryError -Xmx100m The first switch (see minus sign) says that Java creates a heap dump as soon as the main memory emanates. You can also determine how much memory the program is entitled to (see second switch). In our example, the program is interrupted when the program exceeds 100 MB.
Evaluate a Java program
Java usually throws an exception if the above parameters have been used. The MAT can then be used to analyze the heap dump, among other things.
- MAT starts automatically under Eclipse if you click on File> Open File and select the file that ends with .hprof. Alternatively, you can first change the perspective under Eclipse by clicking Window> Perspective> Open Perspective> Other> Memory Analysis . The Open Heap Dump entry then appears in the File menu, which you can use to open the heap dump file.
- The overview window of the evaluated heap dump file is structured like an HTML window so that you can click through the individual points. For example, there is a pie chart on the MAT home page that shows how much memory the individual objects used during runtime before Java interrupted the program.
- The histogram shows the number of instances created per class and how much memory you used during the runtime.
In the next practical tip, read how to program a Java GUI in Eclipse.