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package bjc.utils.ioutils.blocks;
import java.io.IOException;
import java.util.Deque;
import java.util.LinkedList;
/**
* A block reader that supports pushing blocks onto the input queue so that they
* are provided before blocks read from an input source.
*
* @author bjculkin
*
*/
public class PushbackBlockReader implements BlockReader {
private final BlockReader source;
/*
* The queue of pushed-back blocks.
*/
private final Deque<Block> waiting;
private Block curBlock;
private int blockNo;
/**
* Create a new pushback block reader.
*
* @param src
* The block reader to use when no blocks are queued.
*/
public PushbackBlockReader(final BlockReader src) {
source = src;
waiting = new LinkedList<>();
}
@Override
public boolean hasNextBlock() {
return !waiting.isEmpty() || source.hasNextBlock();
}
@Override
public Block getBlock() {
return curBlock;
}
@Override
public boolean nextBlock() {
/*
* Drain pushed-back blocks first.
*/
if (!waiting.isEmpty()) {
curBlock = waiting.pop();
blockNo += 1;
return true;
}
final boolean succ = source.nextBlock();
curBlock = source.getBlock();
if (succ) {
blockNo += 1;
}
return succ;
}
@Override
public int getBlockCount() {
return blockNo;
}
@Override
public void close() throws IOException {
source.close();
}
/**
* Insert a block at the back of the queue of pending blocks.
*
* @param blk
* The block to put at the back.
*/
public void addBlock(final Block blk) {
waiting.add(blk);
}
/**
* Insert a block at the front of the queue of pending blocks.
*
* @param blk
* The block to put at the front.
*/
public void pushBlock(final Block blk) {
waiting.push(blk);
}
@Override
public String toString() {
return String.format("PushbackBlockReader [waiting=%s, curBlock=%s, blockNo=%s]",
waiting, curBlock, blockNo);
}
}
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