OpenJDK 1.23 · java.lang.management.MemoryUsage · APIdia, the JavaDoc alternative

A MemoryUsage object represents a snapshot of memory usage. Instances of the MemoryUsage class are usually constructed by methods that are used to obtain memory usage information about individual memory pool of the Java virtual machine or the heap or non-heap memory of the Java virtual machine as a whole.

A MemoryUsage object contains four values:

Describes the MemoryUsage object content
Value	Description
`init`	represents the initial amount of memory (in bytes) that the Java virtual machine requests from the operating system for memory management during startup. The Java virtual machine may request additional memory from the operating system and may also release memory to the system over time. The value of `init` may be undefined.
`used`	represents the amount of memory currently used (in bytes).
`committed`	represents the amount of memory (in bytes) that is guaranteed to be available for use by the Java virtual machine. The amount of committed memory may change over time (increase or decrease). The Java virtual machine may release memory to the system and `committed` could be less than `init`. `committed` will always be greater than or equal to `used`.
`max`	represents the maximum amount of memory (in bytes) that can be used for memory management. Its value may be undefined. The maximum amount of memory may change over time if defined. The amount of used and committed memory will always be less than or equal to `max` if `max` is defined. A memory allocation may fail if it attempts to increase the used memory such that `used > committed` even if `used <= max` would still be true (for example, when the system is low on virtual memory).

Below is a picture showing an example of a memory pool:

       +----------------------------------------------+
       +////////////////           |                  +
       +////////////////           |                  +
       +----------------------------------------------+

       |--------|
          init
       |---------------|
              used
       |---------------------------|
                 committed
       |----------------------------------------------|
                           max

MXBean Mapping

MemoryUsage is mapped to a CompositeData with attributes as specified in the from method.

Modifier and Type	Field and Description
private final long	committed
private final long	init
private final long	max
private final long	used

Constructor Summary

Access	Constructor and Description
public	MemoryUsage(long the initial amount of memory in bytes that the Java virtual machine allocates; or `-1` if undefined. init, long the amount of used memory in bytes. used, long the amount of committed memory in bytes. committed, long the maximum amount of memory in bytes that can be used; or `-1` if undefined. max) Constructs a `MemoryUsage` object.
private	MemoryUsage(CompositeData cd) Constructs a `MemoryUsage` object from a `CompositeData`.

Method Summary

Modifier and Type	Method and Description
public static MemoryUsage	Returns: a `MemoryUsage` object represented by `cd` if `cd` is not `null`; `null` otherwise. from(CompositeData `CompositeData` representing a `MemoryUsage` cd) Returns a `MemoryUsage` object represented by the given `CompositeData`.
public long	Returns: the amount of committed memory in bytes. getCommitted() Returns the amount of memory in bytes that is committed for the Java virtual machine to use.
public long	Returns: the initial size of memory in bytes; `-1` if undefined. getInit() Returns the amount of memory in bytes that the Java virtual machine initially requests from the operating system for memory management.
public long	Returns: the maximum amount of memory in bytes; `-1` if undefined. getMax() Returns the maximum amount of memory in bytes that can be used for memory management.
public long	Returns: the amount of used memory in bytes. getUsed() Returns the amount of used memory in bytes.
public String	toString() Overrides java.lang.Object.toString. Returns a descriptive representation of this memory usage.

Inherited from java.lang.Object:: clone equals finalize getClass hashCode notify notifyAll wait wait wait

Field Detail

committed	back to summary
private final long committed

init	back to summary
private final long init

max	back to summary
private final long max

used	back to summary
private final long used

Constructor Detail

MemoryUsage back to summary

MemoryUsage	back to summary
public MemoryUsage(long init, long used, long committed, long max) Constructs a `MemoryUsage` object. Parameters init:long the initial amount of memory in bytes that the Java virtual machine allocates; or `-1` if undefined. used:long the amount of used memory in bytes. committed:long the amount of committed memory in bytes. max:long the maximum amount of memory in bytes that can be used; or `-1` if undefined. Exceptions IllegalArgumentException: if the value of `init` or `max` is negative but not `-1`; or the value of `used` or `committed` is negative; or `used` is greater than the value of `committed`; or `committed` is greater than the value of `max` `max` if defined.

public MemoryUsage(long init, long used, long committed, long max)

Constructs a MemoryUsage object.

Parameters

init:long: the initial amount of memory in bytes that the Java virtual machine allocates; or -1 if undefined.
used:long: the amount of used memory in bytes.
committed:long: the amount of committed memory in bytes.
max:long: the maximum amount of memory in bytes that can be used; or -1 if undefined.

Exceptions

IllegalArgumentException:

the value of init or max is negative but not -1; or
the value of used or committed is negative; or
used is greater than the value of committed; or
committed is greater than the value of max max if defined.

MemoryUsage	back to summary
private MemoryUsage(CompositeData cd) Constructs a `MemoryUsage` object from a `CompositeData`.

Method Detail

from back to summary

public static MemoryUsage from(CompositeData cd)

Returns a MemoryUsage object represented by the given CompositeData. The given CompositeData must contain the following attributes:

The attributes and the types the given CompositeData contains
Attribute Name	Type
init	`java.lang.Long`
used	`java.lang.Long`
committed	`java.lang.Long`
max	`java.lang.Long`

Parameters

cd:CompositeData: CompositeData representing a MemoryUsage

Returns:MemoryUsage

a MemoryUsage object represented by cd if cd is not null; null otherwise.

Exceptions

IllegalArgumentException:: if cd does not represent a MemoryUsage with the attributes described above.

getCommitted	back to summary
public long getCommitted() Returns the amount of memory in bytes that is committed for the Java virtual machine to use. This amount of memory is guaranteed for the Java virtual machine to use. Returns:long the amount of committed memory in bytes.

getCommitted

back to summary

public long getCommitted()

Returns the amount of memory in bytes that is committed for the Java virtual machine to use. This amount of memory is guaranteed for the Java virtual machine to use.

Returns:long: the amount of committed memory in bytes.

getInit back to summary

getInit	back to summary
public long getInit() Returns the amount of memory in bytes that the Java virtual machine initially requests from the operating system for memory management. This method returns `-1` if the initial memory size is undefined. Returns:long the initial size of memory in bytes; `-1` if undefined.

public long getInit()

Returns the amount of memory in bytes that the Java virtual machine initially requests from the operating system for memory management. This method returns -1 if the initial memory size is undefined.

Returns:long: the initial size of memory in bytes; -1 if undefined.

getMax back to summary

getMax	back to summary
public long getMax() Returns the maximum amount of memory in bytes that can be used for memory management. This method returns `-1` if the maximum memory size is undefined. This amount of memory is not guaranteed to be available for memory management if it is greater than the amount of committed memory. The Java virtual machine may fail to allocate memory even if the amount of used memory does not exceed this maximum size. Returns:long the maximum amount of memory in bytes; `-1` if undefined.

public long getMax()

Returns the maximum amount of memory in bytes that can be used for memory management. This method returns -1 if the maximum memory size is undefined.

This amount of memory is not guaranteed to be available for memory management if it is greater than the amount of committed memory. The Java virtual machine may fail to allocate memory even if the amount of used memory does not exceed this maximum size.

Returns:long: the maximum amount of memory in bytes; -1 if undefined.

getUsed	back to summary
public long getUsed() Returns the amount of used memory in bytes. Returns:long the amount of used memory in bytes.

getUsed

back to summary

public long getUsed()

Returns the amount of used memory in bytes.

Returns:long: the amount of used memory in bytes.

toString	back to summary
public String toString() Overrides java.lang.Object.toString. Returns a descriptive representation of this memory usage. Returns:String Doc from java.lang.Object.toString. a string representation of the object

toString

back to summary

public String toString()

Overrides java.lang.Object.toString.

Returns a descriptive representation of this memory usage.

Returns:String

Doc from java.lang.Object.toString.

a string representation of the object

public Class MemoryUsage

MXBean Mapping

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail