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 {@link 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 {@link javax.management.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 {@link 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 {@link javax.management.Notification}, with a type of either {@link java.lang.management.MemoryNotificationInfo#MEMORY_THRESHOLD_EXCEEDED} or {@link java.lang.management.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 {@link java.lang.management.MemoryNotificationInfo} contained in the user data section. This is wrapped inside an instance of {@link javax.management.openmbean.CompositeData}, as explained in the documentation for {@link java.lang.management.MemoryNotificationInfo}.
Since: 1.5
| Method Summary | |
|---|---|
| void | gc()
Instigates a garbage collection cycle. |
| MemoryUsage | getHeapMemoryUsage()
Returns a {@link MemoryUsage} object representing the
current state of the heap. |
| MemoryUsage | getNonHeapMemoryUsage()
Returns a {@link 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. |
See Also: gc
Returns: a {@link MemoryUsage} object for the heap.
Returns: a {@link MemoryUsage} object for non-heap memory.
Returns: the number of objects awaiting finalization.
Returns: true if verbose memory output is on.
Parameters: verbose the new setting for verbose memory output.
Throws: SecurityException if a security manager exists and denies ManagementPermission("control").