- java.lang.Object
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- java.lang.management.MemoryUsage
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public class MemoryUsage extends Object
AMemoryUsageobject represents a snapshot of memory usage. Instances of theMemoryUsageclass 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
MemoryUsageobject contains four values:
Below is a picture showing an example of a memory pool:Value Description initrepresents 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 initmay be undefined.usedrepresents the amount of memory currently used (in bytes). committedrepresents 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 committedcould be less thaninit.committedwill always be greater than or equal toused.maxrepresents 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 maxifmaxis defined. A memory allocation may fail if it attempts to increase the used memory such thatused > committedeven ifused <= maxwould still be true (for example, when the system is low on virtual memory).+----------------------------------------------+ +//////////////// | + +//////////////// | + +----------------------------------------------+ |--------| init |---------------| used |---------------------------| committed |----------------------------------------------| maxMXBean Mapping
MemoryUsageis mapped to aCompositeDatawith attributes as specified in thefrommethod.- Since:
- 1.5
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Constructor Summary
Constructors Constructor Description MemoryUsage(long init, long used, long committed, long max)Constructs aMemoryUsageobject.
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description static MemoryUsagefrom(CompositeData cd)Returns aMemoryUsageobject represented by the givenCompositeData.longgetCommitted()Returns 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.StringtoString()Returns a descriptive representation of this memory usage.
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Constructor Detail
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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 Detail
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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
public String toString()
Returns a descriptive representation of this memory usage.
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from
public static MemoryUsage from(CompositeData cd)
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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