Jakarta Commons Cookbook

5.7. Using a Buffer

Problem

You need a data structure that can act as a temporary staging area, i.e., a buffer.

Solution

Use Buffer from Jakarta Commons Collections. A buffer is an object that is defined by the algorithm used for element removal. Buffer objects can be priority queues, staging areas, message queues, or buffers for I/O. One of the simplest Buffer implementations is the UnboundedFifoBuffer, a first-in, first-out data structure with no size limit. The following example demonstrates the use of an UnboundedFifoBuffer:

import org.apache.commons.collections.Buffer;
import org.apache.commons.collections.buffer.UnboundedFifoBuffer;

// Create an Unbounded FIFO
Buffer buffer = new UnboundedFifoBuffer( );

// Add elements to the Buffer
buffer.add("A");
buffer.add("B");
buffer.add("D");

// Remove element from the buffer
String value = (String) buffer.remove( );

buffer.add("E");

value = (String) buffer.remove( );

This example creates an UnboundedFifoBuffer, adding three elements: “A,” “B,” and “D.” When remove() is invoked, the buffer selects the item that was placed into the buffer first—the first-in is the first-out. The first call to remove( ) returns “A,” and the second call returns “B.”

Discussion

A FIFO buffer can be viewed as a kind of stack; instead of pop( ) returning the last item to be placed on the stack, remove( ) returns the bottom of the stack—the first item added to the Buffer. A Buffer throws a BufferUnderflowException if you try to remove( ) or get( ) an element ...