java.lang.management
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.
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
.
Modifier and Type | Method and Description |
---|---|
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.
|
void gc()
java.lang.System.gc()
.System.gc()
MemoryUsage getHeapMemoryUsage()
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.MemoryUsage
object for the heap.MemoryUsage getNonHeapMemoryUsage()
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..MemoryUsage
object for non-heap
memory.int getObjectPendingFinalizationCount()
boolean isVerbose()
void setVerbose(boolean verbose)
verbose
- the new setting for verbose memory output.SecurityException
- if a security manager exists and
denies ManagementPermission("control").