Field Detail

• refSize

  public static final int refSize

• objectOverhead

  private static final int objectOverhead

  See Also:

  Constant Field Values

• booleanSize

  private static final int booleanSize

  See Also:

  Constant Field Values

• charSize

  private static final int charSize

  See Also:

  Constant Field Values

• shortSize

  private static final int shortSize

  See Also:

  Constant Field Values

• intSize

  private static final int intSize

  See Also:

  Constant Field Values

• longSize

  private static final int longSize

  See Also:

  Constant Field Values

• floatSize

  private static final int floatSize

  See Also:

  Constant Field Values

• doubleSize

  private static final int doubleSize

  See Also:

  Constant Field Values

• minObjectSize

  private static final int minObjectSize

• dummyCatalog

  private static boolean dummyCatalog

• noGuess

  static boolean noGuess

• unitTest

  static boolean unitTest

• wildGuess

  private static final int[] wildGuess

Constructor Detail

• ClassSize

  public ClassSize()

Method Detail

• setDummyCatalog

  public static void setDummyCatalog()

  do not try to use the catalog.

• getRefSize

  public static int getRefSize()

  Get the estimate of the size of an object reference.

  Returns:

  the estimate in bytes.

• getIntSize

  public static int getIntSize()

  Returns:

  the estimate of the size of a primitive int

• getSizeCoefficients

  public static int[] getSizeCoefficients​(java.lang.Class cl)

  The estimate of the size of a class instance depends on whether the JVM uses 32 or 64 bit addresses, that is it depends on the size of an object reference. It is a linear function of the size of a reference, e.g. 24 + 5*r where r is the size of a reference (usually 4 or 8 bytes). This method returns the coefficients of the linear function, e.g. {24, 5} in the above example.

  Parameters:

  cl - A class whose instance size is to be estimated

  Returns:

  an array of 2 integers. The first integer is the constant part of the function, the second is the reference size coefficient.

• estimateBaseFromCoefficients

  public static int estimateBaseFromCoefficients​(int[] coeff)

  Estimate the static space taken up by a class instance given the coefficients returned by getSizeCoefficients.

  Parameters:

  coeff - the coefficients

  Returns:

  the size estimate, in bytes

• estimateBaseFromCatalog

  public static int estimateBaseFromCatalog​(java.lang.Class cls)

  Estimate the static space taken up by a class instance from cataloged coefficients.

  Parameters:

  cls - the class

  Returns:

  the size estimate, in bytes

  See Also:

  estimateBaseFromCoefficients(int[]), see org.apache.derbyBuild.ClassSizeCrawler

• estimateBaseFromCatalog

  private static int estimateBaseFromCatalog​(java.lang.Class<?> cls,
                                             boolean addToCatalog)

• estimateAndCatalogBase

  public static int estimateAndCatalogBase​(java.lang.Class cls)

  Estimate the static space taken up by a class instance. Save the coefficients in a catalog.

  Parameters:

  cls - the class

  Returns:

  the size estimate, in bytes

  See Also:

  estimateBaseFromCoefficients(int[]), see org.apache.derbyBuild.ClassSizeCrawler

• estimateBase

  public static int estimateBase​(java.lang.Class cl)

  Estimate the static space taken up by the fields of a class. This includes the space taken up by by references (the pointer) but not by the referenced object. So the estimated size of an array field does not depend on the size of the array. Similarly the size of an object (reference) field does not depend on the object.

  Returns:

  the size estimate in bytes. Note that this method will throw a SecurityException if the SecurityManager does not let this class execute the method Class.getDeclaredFields(). If this is a concern try to compute the size coefficients at build time. see org.apache.derbyBuild.ClassSizeCrawler

  See Also:

  estimateBaseFromCatalog(java.lang.Class)

• estimateArrayOverhead

  public static int estimateArrayOverhead()

  Returns:

  the estimated overhead of an array. The estimated size of an x[n] array is estimateArrayOverhead() + n*sizeOf(x).

• estimateHashEntrySize

  public static int estimateHashEntrySize()

  Estimate the size of a Hashtable entry. In Java 1.2 we can use Map.entry, but this is not available in earlier versions of Java.

  Returns:

  the estimate, in bytes

• estimateMemoryUsage

  public static int estimateMemoryUsage​(java.lang.String str)

  Estimate the size of a string.

  Returns:

  the estimated size, in bytes

• fetchRefSizeFromSystemProperties

  private static final int fetchRefSizeFromSystemProperties()

  Tries to determine the reference size in bytes by checking whether the VM we're running in is 32 or 64 bit by looking at the system properties.

  Returns:

  The reference size in bytes as specified or implied by the VM, or -1 if the reference size couldn't be determined.

• getSystemProperty

  private static final java.lang.String getSystemProperty​(java.lang.String propName)

  Attempts to read the specified system property.

  Parameters:

  propName - name of the system property to read

  Returns:

  The property value, or null if it doesn't exist or the required permission to read the property is missing.