panda.el.parse.CharQueueDefault Maven / Gradle / Ivy

Go to download
package panda.el.parse;

import java.io.IOException;
import java.io.Reader;
import java.util.LinkedList;

/**
 * 字符队列默认实现.
 */
public class CharQueueDefault implements CharQueue {
	private Reader reader;
	private LinkedList cache;
	private int cursor;

	public CharQueueDefault(Reader reader) {
		this.reader = reader;
		cache = new LinkedList();
		try {
			cursor = reader.read();
		}
		catch (IOException e) {
			e.printStackTrace();
		}
	}

	public char peek() {
		return (char)cursor;
	}

	public char peek(int ofset) {
		if (ofset == 0) {
			return (char)cursor;
		}
		// 这个地方因为已经预读了cursor 所以,偏移量要向后移动一位
		if (cache.size() > ofset - 1) {
			return (char)cache.get(ofset - 1).intValue();
		}
		int t = 0;
		for (int i = 0; i < ofset - cache.size(); i++) {
			try {
				t = reader.read();
				cache.add(t);
			}
			catch (IOException e) {
				e.printStackTrace();
			}
		}
		return (char)t;
	}

	public char poll() {
		char x = (char)cursor;
		try {
			if (cache.isEmpty()) {
				cursor = reader.read();
			}
			else {
				cursor = cache.poll();
			}
		}
		catch (IOException e) {
			e.printStackTrace();
		}
		return x;
	}

	public boolean isEmpty() {
		return cursor == -1;
	}

}