Decrement by 1, return previous

Atomically decrements by one the current value and returns the previous value of the counter. It is possible that multiple concurrent client requests may receive the same previous value. This occurs since only the decrementing part of the logic is atomic, the retrieval of the value before it is decremented is not.

// *******************************************
// synchronous methods
// *******************************************

// Backendless.Counters approach
public Long Backendless.Counters.getAndDecrement( String counterName );

// IAtomic approach
IAtomic<T> counter = Backendless.Counters.of( String counterName, 
                                                    Class<? extends T> type );
public T counter.getAndIncrement();

// *******************************************
// asynchronous methods
// *******************************************

// Backendless.Counters approach
public <T> T Backendless.Counters.getAndDecrement( String counterName, 
                                                         AsyncCallback<T> callback );

// IAtomic approach
IAtomic<T> counter = Backendless.Counters.of( String counterName, 
                                                    Class<? extends T> type );
public T counter.getAndDecrement( AsyncCallback<T> callback );

where:

Argument	Description
counterName	name of the counter to decrement.
type	numeric type for the counter values. Can be an instance of Byte.class, Short.class, Integer.class, Float.class, Long.class and Double.class.
callback	the callback used for asynchronous calls to indicate that the operation has either successfully completed or resulted in error.

Example

AsyncCallback<Integer> callback = new AsyncCallback<Integer>()
{
  @Override
  public void handleResponse( Integer value )
  {
    Log.i( "MYAPP", "[ASYNC] previous counter value is - " + value );
  }

  @Override
  public void handleFault( BackendlessFault backendlessFault )
  {
    Log.e( "MYAPP", "Error - " + backendlessFault.getMessage() );
  }
};

Backendless.Counters.getAndDecrement( "my counter", callback );

IAtomic<Integer> myCounter = Backendless.Counters.of( "my counter", Integer.class );
int counterValue = myCounter.getAndDecrement();
Log.i( "MYAPP", "[SYNC] previous counter value is - " + counterValue );

Codeless Reference

where:

Argument	Description
counter name	Name of the counter whose value must be decremented.
return previous value	When this box is checked, the operation returns the previous value of the counter.

Returns the previous value of the counter, while decrementing the value by 1.

Consider the following counter:

The example below decrements the value of the "CarsParkingLot" by 1. This operation returns 10, since the return previous value box is checked. To avoid confusion, the value was decremented by 1, even though the return value is 10.

The result of this operation will look as shown below after the Codeless logic runs, as you can see the value of the counter was decremented by 1.