Class MemoryUsage
- java.lang.Object
-
- java.lang.management.MemoryUsage
public class MemoryUsage extends Object
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:
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). |
+----------------------------------------------+ +//////////////// | + +//////////////// | + +----------------------------------------------+ |--------| init |---------------| used |---------------------------| committed |----------------------------------------------| max
MXBean Mapping
MemoryUsage
is mapped to a CompositeData
with attributes as specified in the from
method.- Since:
- 1.5
Constructor Summary
Constructor | Description |
---|---|
MemoryUsage(long init,
long used,
long committed,
long max) | Constructs a |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
static MemoryUsage | from(CompositeData cd) | Returns a |
long | getCommitted() | Returns the amount of memory in bytes that is committed for the Java virtual machine to use. |
long | getInit() | Returns the amount of memory in bytes that the Java virtual machine initially requests from the operating system for memory management. |
long | getMax() | Returns the maximum amount of memory in bytes that can be used for memory management. |
long | getUsed() | Returns the amount of used memory in bytes. |
String | toString() | Returns a descriptive representation of this memory usage. |
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Constructor Detail
MemoryUsage
public MemoryUsage(long init, long used, long committed, long max)
Constructs a MemoryUsage
object.
- Parameters:
-
init
- the initial amount of memory in bytes that the Java virtual machine allocates; or-1
if undefined. -
used
- the amount of used memory in bytes. -
committed
- the amount of committed memory in bytes. -
max
- the maximum amount of memory in bytes that can be used; or-1
if undefined. - Throws:
-
IllegalArgumentException
- if- the value of
init
ormax
is negative but not-1
; or - the value of
used
orcommitted
is negative; or -
used
is greater than the value ofcommitted
; or -
committed
is greater than the value ofmax
max
if defined.
- the value of
Method Detail
getInit
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:
- the initial size of memory in bytes;
-1
if undefined.
getUsed
public long getUsed()
Returns the amount of used memory in bytes.
- Returns:
- the amount of used memory in bytes.
getCommitted
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:
- the amount of committed memory in bytes.
getMax
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:
- the maximum amount of memory in bytes;
-1
if undefined.
toString
public String toString()
Returns a descriptive representation of this memory usage.
from
public static MemoryUsage from(CompositeData cd)
Returns a MemoryUsage
object represented by the given CompositeData
. The given CompositeData
must contain the following attributes:
Attribute Name | Type |
---|---|
init | java.lang.Long |
used | java.lang.Long |
committed | java.lang.Long |
max | java.lang.Long |
- Parameters:
-
cd
-CompositeData
representing aMemoryUsage
- Returns:
- a
MemoryUsage
object represented bycd
ifcd
is notnull
;null
otherwise. - Throws:
-
IllegalArgumentException
- ifcd
does not represent aMemoryUsage
with the attributes described above.