java.lang.management
Class MemoryUsage

java.lang.Object
  java.lang.management.MemoryUsage

All Implemented Interfaces:

Serializable

public class MemoryUsage

extends Object

implements Serializable

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.
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 memory will always be less than or equal to max if max is defined. It could be greater than or less than committed. 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
        |---------------------------|
                   max
        |----------------------------------------------|
                               committed
 

Since:

1.5

See Also:

Serialized Form

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.

IllegalArgumentException - if used is greater than the value of committed or max if not -1.

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 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.