public interface MemoryMonitor
For Java4, the available monitors do nothing since there is no reliable way of detecting that memory is running low using such a JVM (you are welcome to try to create one, but I believe you will fail - some such candidates only make it more likely that an OutOfMemory condition will occur).
For Java5 one can optionally enable a monitor which is based upon the Java5 memory classes locate in java.lang.management.
A client must implement the MemoryMonitor.Listener interface
and register with the MemoryMonitor.
The MemoryMonitor supports having multiple
Listener clients. The clients can have the same
threshold percentage or different values. The threshold percentage value
is used by the MemoryMonitor to determine when to
notify a client. It is the percentage of the total memory:
100 * free-memory / total-memory (0 ≤ free-memory ≤ total-memory).
| Modifier and Type | Interface and Description |
|---|---|
static interface |
MemoryMonitor.Listener
A
MemoryMonitor client implements the Listener
interface and registers with the MemoryMonitor. |
static interface |
MemoryMonitor.Test
This is an interface that a
MemoryMonitor may optionally
implement. |
| Modifier and Type | Method and Description |
|---|---|
boolean |
addListener(MemoryMonitor.Listener listener)
Adds a
Listener using the default threshold percentage. |
boolean |
addListener(MemoryMonitor.Listener listener,
int thresholdPercentage)
Adds a
Listener to the MemoryMonitor with
a given threshold percentage. |
long |
getMaxMemory()
Returns the maximum memory usage.
|
long |
getUsedMemory()
Returns the current memory used.
|
void |
removeAllListener()
Clear out all
Listeners and turnoff JVM
memory notification. |
boolean |
removeListener(MemoryMonitor.Listener listener)
Removes a
Listener from the MemoryMonitor. |
void |
updateListenerThreshold(MemoryMonitor.Listener listener,
int percentage)
Changes the threshold percentage of a given
Listener. |
boolean addListener(MemoryMonitor.Listener listener, int thresholdPercentage)
Listener to the MemoryMonitor with
a given threshold percentage.
If the threshold is below the Java5 memory managment system's threshold, then the Listener is notified from within this method.
listener - the Listener to be added.thresholdPercentage - the threshold percentage for this
Listener.true if the Listener was
added and false otherwise.boolean addListener(MemoryMonitor.Listener listener)
Listener using the default threshold percentage.
If the threshold is below the Java5 memory managment system's threshold, then the Listener is notified from within this method.
listener - the Listener to be added.true if the Listener was
added and false otherwise.void updateListenerThreshold(MemoryMonitor.Listener listener, int percentage)
Listener.
If the new value is below the system's current value, then the
Listener will have its notification callback called
while in this method - so a client should always check if its
notification method was called immediately after calling this
method.
This method can be used if, for example, an algorithm has different approaches that result in different memory usage profiles; one, large memory but fast and a second which is low-memory but slow. The algorithm starts with the large memory approach, receives a low memory notification, switches to the low memory approach and changes when it should be notified for this new approach. The first approach need to be notified at a lower percentage because it uses lots of memory, possibly quickly; while the second approach, possibly a file based algorithm, has smaller memory requirements and uses memory less quickly thus one can live with a higher notification threshold percentage.
listener - the Listener being updated.percentage - new percentage threshold.boolean removeListener(MemoryMonitor.Listener listener)
Listener from the MemoryMonitor.
Returns true if listener was removed and
false otherwise.listener - the listener to be removedtrue if listener was removed.void removeAllListener()
Listeners and turnoff JVM
memory notification.long getMaxMemory()
long getUsedMemory()