Java™ Platform
Standard Ed. 6

java.lang.management
Class MemoryUsage

java.lang.Object
  extended by 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:

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.

Since:
1.5

Constructor Summary
MemoryUsage(long init, long used, long committed, long max)
          Constructs a MemoryUsage object.
 
Method Summary
static MemoryUsage from(CompositeData cd)
          Returns a MemoryUsage object represented by the given CompositeData.
 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 inherited from 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 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.
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.

Overrides:
toString in class Object
Returns:
a string representation of the object.

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 a MemoryUsage
Returns:
a MemoryUsage object represented by cd if cd is not null; null otherwise.
Throws:
IllegalArgumentException - if cd does not represent a MemoryUsage with the attributes described above.

Java™ Platform
Standard Ed. 6

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For further API reference and developer documentation, see Java SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

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