com.tridion.util

Class ObjectSize

java.lang.Object

com.tridion.util.ObjectSize

public final class ObjectSize
extends Object

Utility class for calculating object sizes statically. This seems to be as precise as JOL for JVM with heap < 32GB (for all the covered scenarios see ObjectSizeVsJolTest). For heap >32GB this overestimates by maximum 25% compared to JOL. This happens because each JVM might be a bit different and this tool is static, compared to JOL that gets the object size dynamically (from the JVM, at runtime).

Security. This implementation uses AccessController.doPrivileged() so it could be granted privileges to access non-public class fields separately from the application code. The minimum set of permissions necessary for this class to function correctly follows:

 permission java.lang.RuntimePermission "accessDeclaredMembers";
 permission java.lang.reflect.ReflectPermission "suppressAccessChecks";
 

We tried to align with all the information from here: https://shipilev.net/jvm/objects-inside-out/

Remember, that after every update of JDK 7+ and higher the size of objects can be changed. If, suddenly, you'll notice unexpected behaviour in object size measurement, use memory-measurer project for check the size in bytes. Keep the basic size of int fields up-to-date.

Field Summary

Fields

Modifier and Type	Field and Description
static int	SIZE_ARRAY_OBJECT Size of an array object in bytes.
static int	SIZE_BOOLEAN_FIELD Size of a boolean field in bytes.
static int	SIZE_BYTE_FIELD Size of a byte field in bytes.
static int	SIZE_CHAR_FIELD Size of a char field in bytes.
static int	SIZE_DATE_OBJECT Size of a Date object in bytes, assuming it does not use a Calender.
static int	SIZE_DOUBLE_FIELD Size of a double field in bytes.
static int	SIZE_FLOAT_FIELD Size of a float field in bytes.
static int	SIZE_INT_FIELD Size of a int field in bytes.
static int	SIZE_LONG_FIELD Size of a long field in bytes.
static int	SIZE_OBJECT_BASE Basic size of an object in bytes.
static int	SIZE_OBJECT_REF Size of an object reference field in bytes.
static int	SIZE_SHORT_FIELD Size of a short field in bytes.

Method Summary

Modifier and Type	Method and Description
static int	getAlignment(int sizeWithoutAlign) Any java object is placed in memory with alignment to 8 bytes.
static int	sizeof(Object obj) Estimates the size of the object graph rooted at the specified object.
static int	sizeofString(String s) Deprecated. use sizeof

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

SIZE_OBJECT_BASE

public static final int SIZE_OBJECT_BASE

Basic size of an object in bytes.

SIZE_OBJECT_REF

public static final int SIZE_OBJECT_REF

Size of an object reference field in bytes.

SIZE_LONG_FIELD

public static final int SIZE_LONG_FIELD

Size of a long field in bytes.

See Also:

Constant Field Values

SIZE_INT_FIELD

public static final int SIZE_INT_FIELD

Size of a int field in bytes.

See Also:

Constant Field Values

SIZE_SHORT_FIELD

public static final int SIZE_SHORT_FIELD

Size of a short field in bytes.

See Also:

Constant Field Values

SIZE_CHAR_FIELD

public static final int SIZE_CHAR_FIELD

Size of a char field in bytes.

See Also:

Constant Field Values

SIZE_BYTE_FIELD

public static final int SIZE_BYTE_FIELD

Size of a byte field in bytes.

See Also:

Constant Field Values

SIZE_BOOLEAN_FIELD

public static final int SIZE_BOOLEAN_FIELD

Size of a boolean field in bytes.

See Also:

Constant Field Values

SIZE_DOUBLE_FIELD

public static final int SIZE_DOUBLE_FIELD

Size of a double field in bytes.

See Also:

Constant Field Values

SIZE_FLOAT_FIELD

public static final int SIZE_FLOAT_FIELD

Size of a float field in bytes.

See Also:

Constant Field Values

SIZE_ARRAY_OBJECT

public static final int SIZE_ARRAY_OBJECT

Size of an array object in bytes.

SIZE_DATE_OBJECT

public static final int SIZE_DATE_OBJECT

Size of a Date object in bytes, assuming it does not use a Calender.

UPD: In Java 8 java.util.Date object's size is 28 bytes. Please refer to top class javadoc for further details.

See Also:

Constant Field Values

Method Detail

sizeofString

@Deprecated
public static int sizeofString(String s)

Deprecated. use sizeof

The original implementation was returning a lower memory size value than what JOL calculates therefore I was refactored to use sizeof(s) (which returns a higher size than what JOL calculates). See class ajvadoc for overestimating VS underestimating memsize

Parameters:

s - the string to estimate the size of; may be null.

Returns:

The size of the string in bytes.

sizeof

public static int sizeof(Object obj)

Estimates the size of the object graph rooted at the specified object. Alignment of fields is ignored by design.

Parameters:

obj - the object to estimate the size of.

Returns:

The size of the object in bytes; may be null.

Throws:

RuntimeException - Thrown if the method failed to access fields of an object in the object graph, probably for security reasons.

getAlignment

public static int getAlignment(int sizeWithoutAlign)

Any java object is placed in memory with alignment to 8 bytes. So it needs to be included into total size computation.

Parameters:

sizeWithoutAlign - size of object without align

Returns:

total object size