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| java.lang.Object
 java.lang.management.MemoryUsage
| MemoryUsage | | public class MemoryUsage (Code) | | 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:
| 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.
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| used |
represents the amount of memory currently used (in bytes).
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| 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.
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| 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).
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Below is a picture showing an example of a memory pool:
+----------------------------------------------+
+//////////////// | +
+//////////////// | +
+----------------------------------------------+
|--------|
init
|---------------|
used
|---------------------------|
committed
|----------------------------------------------|
max
MXBean Mapping
MemoryUsage is mapped to a
CompositeData CompositeData with attributes as specified in the
MemoryUsage.from from method.
author:
Mandy Chung
version:
1.23, 05/05/07
since:
1.5 |
| Constructor Summary | |
| public | MemoryUsage(long init, long used, long committed, long max)
Constructs a MemoryUsage object. |
| Method Summary | |
| public static MemoryUsage | from(CompositeData cd)
Returns a MemoryUsage object represented by the
given CompositeData. | | public long | getCommitted()
Returns the amount of memory in bytes that is committed for
the Java virtual machine to use. | | public long | getInit()
Returns the amount of memory in bytes that the Java virtual machine
initially requests from the operating system for memory management. | | public long | getMax()
Returns the maximum amount of memory in bytes that can be
used for memory management. | | public long | getUsed()
Returns the amount of used memory in bytes. | | public String | toString()
Returns a descriptive representation of this memory usage. |
| MemoryUsage | | public MemoryUsage(long init, long used, long committed, long max)(Code) | | Constructs a MemoryUsage object.
Parameters:
init - the initial amount of memory in bytes thatthe Java virtual machine allocates;or -1 if undefined.
Parameters:
used - the amount of used memory in bytes.
Parameters:
committed - the amount of committed memory in bytes.
Parameters:
max - the maximum amount of memory in bytes thatcan be used; or -1 if undefined.
throws:
IllegalArgumentException - if- the value of init or max is negativebut 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.
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| from | | public static MemoryUsage from(CompositeData cd)(Code) | | 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 a MemoryUsage
throws:
IllegalArgumentException - if cd does notrepresent a MemoryUsage with the attributes describedabove. a MemoryUsage object represented by cdif cd is not null;null otherwise. |
| getCommitted | | public long getCommitted()(Code) | | 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.
the amount of committed memory in bytes. |
| getInit | | public long getInit()(Code) | | 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.
the initial size of memory in bytes;-1 if undefined. |
| getMax | | public long getMax()(Code) | | 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.
the maximum amount of memory in bytes; -1 if undefined. |
| getUsed | | public long getUsed()(Code) | | Returns the amount of used memory in bytes.
the amount of used memory in bytes. |
| toString | | public String toString()(Code) | | Returns a descriptive representation of this memory usage.
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