java.lang.management
Interface MemoryMXBean
Provides access to information about the memory used
by the virtual machine. An instance of this bean is
obtained by calling
ManagementFactory.getMemoryMXBean().
The Java virtual machine uses two types of memory:
heap memory and non-heap memory. The heap is the
storage location for class and array instances, and is
thus the main source of memory associated with running
Java programs. The heap is created when the virtual
machine is started, and is periodically scanned by the
garbage collector(s), in order to reclaim memory which
is no longer used (e.g. because an object reference has
gone out of scope).
Non-heap memory is used by the virtual machine in order to
perform its duties. Thus, it mainly acts as the storage
location for structures created as a result of parsing Java
bytecode, such as the constant pool and constructor/method
declarations. When a Just-In-Time (JIT) compiler is in
operation, this will use non-heap memory to store compiled
bytecode.
Both types of memory may be non-contiguous. During the
lifetime of the virtual machine, the size of both may
either change (either expanding or contracting) or stay
the same.
Notifications
Implementations of this interface also conform to the
NotificationEmitter interface,
and supply two notifications reflecting memory usage.
These notifications occur when a usage threshold is
exceeded; for more details of these, see the documentation
of
MemoryPoolMXBean. If threshold monitoring
is supported, then a notification will be emitted each time
the threshold is crossed. Another notification will not
be emitted unless the usage level has dropped below the
threshold again in the meantime.
The emitted notifications are instances of
Notification, with a type of
either
MemoryNotificationInfo.MEMORY_THRESHOLD_EXCEEDED
or
MemoryNotificationInfo.MEMORY_COLLECTION_THRESHOLD_EXCEEDED
(depending on whether the notification refers to the general
usage threshold or the garbage collection threshold) and an instance
of
MemoryNotificationInfo contained
in the user data section. This is wrapped inside an instance
of
CompositeData, as explained
in the documentation for
MemoryNotificationInfo.
gc
public void gc()
Instigates a garbage collection cycle. The virtual
machine's garbage collector should make the best
attempt it can at reclaiming unused memory. This
is equivalent to invoking java.lang.System.gc().
getHeapMemoryUsage
public MemoryUsage getHeapMemoryUsage()
Returns a
MemoryUsage object representing the
current state of the heap. This incorporates various
statistics on both the initial and current memory
allocations used by the heap.
getNonHeapMemoryUsage
public MemoryUsage getNonHeapMemoryUsage()
Returns a
MemoryUsage object representing the
current state of non-heap memory. This incorporates
various statistics on both the initial and current
memory allocations used by non-heap memory..
getObjectPendingFinalizationCount
public int getObjectPendingFinalizationCount()
Returns the number of objects which are waiting to
be garbage collected (finalized). An object is
finalized when the garbage collector determines that
there are no more references to that object are in
use.
- the number of objects awaiting finalization.
isVerbose
public boolean isVerbose()
Returns true if the virtual machine will emit additional
information when memory is allocated and deallocated. The
format of the output is left up to the virtual machine.
- true if verbose memory output is on.
setVerbose
public void setVerbose(boolean verbose)
Turns on or off the emission of additional information
when memory is allocated and deallocated. The format of the
output is left up to the virtual machine. This method
may be called by multiple threads concurrently, but there
is only one global setting of verbosity that is affected.
verbose - the new setting for verbose memory output.
SecurityException - if a security manager exists and
denies ManagementPermission("control").
MemoryMXBean.java - Interface for a memory bean
Copyright (C) 2006 Free Software Foundation
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