Determining size of Java objects.
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README.md

sizeofag

sizeofag is a Java Agent that allows you to determine the size of Java objects from within the JVM at runtime. This makes it very useful for developing Java frameworks that take memory constraints into account. This project is based on Maxim Zakharenkov's code.

sizeofag is used, for instance, in MOA (Massive Online Analysis), a machine learning framework for data streams.

License

sizeofag is released under LGPL 3.

Maven

Include the following dependency in your pom.xml:

<dependency>
    <groupId>com.github.fracpete</groupId>
    <artifactId>sizeofag</artifactId>
    <version>1.0.4</version>
</dependency>

NB: You still need to add the -javaagent parameter to your Java call. See example below for details.

Examples

You have to start up the JVM with the following additional parameter (adjusting the path to the jar, of course):

-javaagent:/path/to/sizeofag-1.0.4.jar

Total size

The following example code:

import sizeof.agent.SizeOfAgent;

public class SizeTest {

  double d;
  float f;
  int i;
  long l;

  public static void main(String[] args) throws Exception {
    System.out.println(SizeOfAgent.fullSizeOf(new String("Hello World")));
    System.out.println(SizeOfAgent.fullSizeOf(2));
    System.out.println(SizeOfAgent.fullSizeOf(2.3));
    System.out.println(SizeOfAgent.fullSizeOf(1.5f));
    System.out.println(SizeOfAgent.fullSizeOf(new SizeTest()));
  }
}

will output something like this (9.0.4, 64bit on Linux):

56
16
24
16
40

Breakdown per class

It is also possible to break down the size per class by using the fullSizePerClass method as in the following example. This method returns a map of Class to sizeof.agent.Statistics relation, with the Statistics container class containing the accumulated size for the class and the number of instances of this object were encountered.

public class SizeTest {

  double d;
  float f;
  int i;
  long l;

  public static class InnerClass {
    double d;
    float f;
  }

  public static class AnotherClass {
    InnerClass inner = new InnerClass();
  }

  AnotherClass another1 = new AnotherClass();
  AnotherClass another2 = new AnotherClass();
  AnotherClass another3 = new AnotherClass();
  InnerClass inner1 = new InnerClass();
  InnerClass inner2 = new InnerClass();

  public static void main(String[] args) throws Exception {
    System.out.println("AnotherClass (full): " + SizeOfAgent.fullSizeOf(new AnotherClass()));
    System.out.println("InnerClass (full): " + SizeOfAgent.fullSizeOf(new InnerClass()));
    System.out.println("SizeTest (full): " + SizeOfAgent.fullSizeOf(new SizeTest()));
    System.out.println("AnotherClass (per class): " + SizeOfAgent.fullSizePerClass(new AnotherClass()));
    System.out.println("InnerClass (per class): " + SizeOfAgent.fullSizePerClass(new InnerClass()));
    System.out.println("SizeTest (per class): " + SizeOfAgent.fullSizePerClass(new SizeTest()));
  }
}

Will output something like this (9.0.4, 64bit on Linux):

AnotherClass (full): 40
InnerClass (full): 24
SizeTest (full): 224
AnotherClass (per class): {class sizeof.agent.SizeTest$AnotherClass={count:1, total:16}, class sizeof.agent.SizeTest$InnerClass={count:1, total:24}}
InnerClass (per class): {class sizeof.agent.SizeTest$InnerClass={count:1, total:24}}
SizeTest (per class): {class sizeof.agent.SizeTest$AnotherClass={count:3, total:48}, class sizeof.agent.SizeTest={count:1, total:56}, class sizeof.agent.SizeTest$InnerClass={count:5, total:120}}

Filtering

With the sizeof.agent.Filter class, you can influence how the calculation and traversal is occurring:

  • public boolean skipSuperClass(Class superclass);

    Allows you to stop the traversal up the class hierarchy.

  • public boolean skipObject(Object obj);

    Here you can skip certain objects, e.g., ones that implement a certain interface. The supplied object, however, is always inspected.

  • public boolean skipField(Field field);

    With this method, you can avoid specific fields declared by the class of the current object.

The following example class will skip instances of InnerClass in its calculation:

public class SizeTest {

  double d;
  float f;
  int i;
  long l;

  public static class InnerClass {
    double d;
    float f;
  }

  public static class AnotherClass {
    InnerClass inner = new InnerClass();
  }

  AnotherClass another1 = new AnotherClass();
  AnotherClass another2 = new AnotherClass();
  AnotherClass another3 = new AnotherClass();
  InnerClass inner1 = new InnerClass();
  InnerClass inner2 = new InnerClass();

  public static void main(String[] args) throws Exception {
    Filter filter = new Filter() {
      public boolean skipSuperClass(Class superclass) {
	return false;
      }
      public boolean skipObject(Object obj) {
	return (obj instanceof InnerClass);
      }
      public boolean skipField(Field field) {
	return false;
      }
    };
    System.out.println("AnotherClass (per class): " + SizeOfAgent.fullSizePerClass(new AnotherClass(), filter));
    System.out.println("InnerClass (per class): " + SizeOfAgent.fullSizePerClass(new InnerClass(), filter));
    System.out.println("SizeTest (per class): " + SizeOfAgent.fullSizePerClass(new SizeTest(), filter));
  }
}

Will output something like this (9.0.4, 64bit on Linux):

AnotherClass (per class): {class sizeof.agent.SizeTest$AnotherClass={count:1, total:16}}
InnerClass (per class): {class sizeof.agent.SizeTest$InnerClass={count:1, total:24}}
SizeTest (per class): {class sizeof.agent.SizeTest={count:1, total:56}, class sizeof.agent.SizeTest$AnotherClass={count:3, total:48}}