The Eclipse MAT tooling is a set of Eclipse plug-ins which visualize the references to objects based on Java heap dumps and provides tools to identify potential memory leaks.

The garbage collector of the JVM releases Java objects from memory as long as no other object refers to this object.

A Java heap dump is a snapshot of the complete Java object graph at a certain point in time. It includes all objects, fields, primitive types and object references.

It is possible to instruct the JVM to create automatically a heap dump in case that it runs out of memory, i.e. in case of a OutOfMemoryError error. To instruct the JVM to create a heap dump in such a situation, start your Java application with the -XX:+HeapDumpOnOutOfMemoryError option.

Android allows to create heap dumps of an application's heap. This heap dump is stored in a binary format called HPROF. To create a heap dump us the Dump HPROF file button in the DDMS Perspective.

The Dalvik format is similar to the Java heap dump format. To convert the Dalvik heap dump to the Java heap format you can use the hprof-conv source target command.

After a new heap dump with the .hprof ending has been created, you can open it via a double-click in Eclipse. You may need to refresh your project (F5 on the project). Double-click the file and select the Leak Suspects Report.

The overview page allows you to start the analysis of the heap dump. The dominator tree gives quickly an overview of the used objects.

Create the Java project called com.vogella.mat.first and the com.vogella.mat.first package. Create the following class.

package com.vogella.mat.first;

import java.util.ArrayList;
import java.util.List;

public class Main {

  
/**
   * @param args
   */
  public static void main(String[] args) {
    List<String> list = new ArrayList<String>();
    while (1<2){
      list.add("OutOfMemoryError soon");
    }

  }

} 

In Eclipse add the -XX:+HeapDumpOnOutOfMemoryError to the runtime configuration.

Run the project. It crashes and write an heap dump.

Source Code of Examples

How to aquire a Heap Dump from MAT

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