Class MemoryUsage
java.lang.Object
java.lang.management.MemoryUsage
A
Below is a picture showing an example of a memory pool:
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
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Constructor Summary
ConstructorsConstructorDescriptionMemoryUsage(long init, long used, long committed, long max) Constructs aMemoryUsageobject. -
Method Summary
Modifier and TypeMethodDescriptionstatic MemoryUsagefrom(CompositeData cd) Returns aMemoryUsageobject represented by the givenCompositeData.longReturns the amount of memory in bytes that is committed for the Java virtual machine to use.longgetInit()Returns the amount of memory in bytes that the Java virtual machine initially requests from the operating system for memory management.longgetMax()Returns the maximum amount of memory in bytes that can be used for memory management.longgetUsed()Returns the amount of used memory in bytes.toString()Returns a descriptive representation of this memory usage.
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Constructor Details
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MemoryUsage
public MemoryUsage(long init, long used, long committed, long max) Constructs aMemoryUsageobject.- Parameters:
init- the initial amount of memory in bytes that the Java virtual machine allocates; or-1if 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-1if undefined.- Throws:
IllegalArgumentException- if- the value of
initormaxis negative but not-1; or - the value of
usedorcommittedis negative; or -
usedis greater than the value ofcommitted; or -
committedis greater than the value ofmaxmaxif defined.
- the value of
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Method Details
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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-1if the initial memory size is undefined.- Returns:
- the initial size of memory in bytes;
-1if undefined.
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getUsed
public long getUsed()Returns the amount of used memory in bytes.- Returns:
- the amount of used memory in bytes.
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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.
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getMax
public long getMax()Returns the maximum amount of memory in bytes that can be used for memory management. This method returns-1if 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;
-1if undefined.
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toString
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from
Returns aMemoryUsageobject represented by the givenCompositeData. The givenCompositeDatamust contain the following attributes:Attribute Name Type init java.lang.Longused java.lang.Longcommitted java.lang.Longmax java.lang.Long- Parameters:
cd-CompositeDatarepresenting aMemoryUsage- Returns:
- a
MemoryUsageobject represented bycdifcdis notnull;nullotherwise. - Throws:
IllegalArgumentException- ifcddoes not represent aMemoryUsagewith the attributes described above.
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