Ring Buffer in Java

Question

I have a streaming time series, of which I am interested in keeping the last 4 elements, which means I want to be able to pop the first, and add to the end. Essentially what I need is a ring buffer.

Which Java Collection is the best for this? Vector?

Answer 1

Consider CircularFifoBuffer from Apache Common.Collections. Unlike Queue you don't have to maintain the limited size of underlying collection and wrap it once you hit the limit.

Buffer buf = new CircularFifoBuffer(4); buf.add("A"); buf.add("B"); buf.add("C"); buf.add("D"); //ABCD buf.add("E"); //BCDE 

CircularFifoBuffer will do this for you because of the following properties:

• CircularFifoBuffer is a first in first out buffer with a fixed size that replaces its oldest element if full.
• The removal order of a CircularFifoBuffer is based on the insertion order; elements are removed in the same order in which they were added. The iteration order is the same as the removal order.
• The add(Object), BoundedFifoBuffer.remove() and BoundedFifoBuffer.get() operations all perform in constant time. All other operations perform in linear time or worse.

However you should consider it's limitations as well - for example, you can't add missing timeseries to this collection because it doens't allow nulls.

NOTE: When using current Common Collections (4.*), you have to use Queue. Like this:

Queue buf = new CircularFifoQueue(4);