java.lang.management

Interface MemoryMXBean

Known Implementing Classes:
MemoryMXBeanImpl

public 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.

Since:
1.5

Method Summary

void
gc()
Instigates a garbage collection cycle.
MemoryUsage
getHeapMemoryUsage()
Returns a MemoryUsage object representing the current state of the heap.
MemoryUsage
getNonHeapMemoryUsage()
Returns a MemoryUsage object representing the current state of non-heap memory.
int
getObjectPendingFinalizationCount()
Returns the number of objects which are waiting to be garbage collected (finalized).
boolean
isVerbose()
Returns true if the virtual machine will emit additional information when memory is allocated and deallocated.
void
setVerbose(boolean verbose)
Turns on or off the emission of additional information when memory is allocated and deallocated.

Method Details

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().
See Also:
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.
Returns:
a MemoryUsage object for 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..
Returns:
a MemoryUsage object for 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.
Returns:
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.
Returns:
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.
Parameters:
verbose - the new setting for verbose memory output.
Throws:
SecurityException - if a security manager exists and denies ManagementPermission("control").

MemoryMXBean.java - Interface for a memory bean Copyright (C) 2006 Free Software Foundation This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.