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SPL(Structured Process Language) A programming language specially for structured data computing.

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package com.scudata.common;

import java.util.EmptyStackException;
import java.util.Vector;

/**
 * ???ƴ?С?Ķ???
 */
public final class LimitedQueue {

	/**
	 * ?????ij?Ա????
	 */
	private int maxSize = Integer.MAX_VALUE;
	/**
	 * ????
	 */
	private Vector stack = new Vector();

	/**
	 * ?Ƿ????˱仯
	 */
	private boolean changed = false;

	/**
	 * ???캯??
	 */
	public LimitedQueue() {
	}

	/**
	 * ???캯??
	 * 
	 * @param maxSize
	 *            ??󳤶?
	 */
	public LimitedQueue(int maxSize) {
		if (maxSize <= 0) {
			throw new IllegalArgumentException("limit must be bigger than 0");
		}
		this.maxSize = maxSize;
	}

	/**
	 * ȡ?Ƿ????˱仯
	 * 
	 * @return
	 */
	public boolean isChanged() {
		return changed;
	}

	/**
	 * ?????Ƿ????˱仯
	 */
	public void setUnChanged() {
		changed = false;
	}

	/**
	 * ??????󳤶ȣ?????????????ȵ?????
	 */
	public void setMaxSize(int maxSize) {
		if (maxSize <= 0) {
			throw new IllegalArgumentException("limit must be bigger than 0");
		}
		this.maxSize = maxSize;
		while (maxSize < size()) {
			stack.removeElementAt(size() - 1);
		}
		changed = true;
	}

	/**
	 * ȡ??ջ??󳤶?
	 */
	public int getMaxSize() {
		return maxSize;
	}

	/**
	 * ȡ??ջ??Ԫ?ظ???
	 */
	public int size() {
		return stack.size();
	}

	/**
	 * Ԫ?ؽ???ջ??
	 * 
	 * @param item
	 *            ??ջ??Ԫ??
	 */

	public Object add(Object item) {
		if (size() >= maxSize) {
			stack.removeElementAt(0);
		}
		stack.addElement(item);
		changed = true;
		return item;
	}

	/**
	 * ?????ȡ??Ա
	 * 
	 * @param index
	 *            ???
	 * @return
	 */
	public Object get(int index) {
		return stack.get(index);
	}

	/**
	 * ???׸?Ԫ?شӶ????е?????????????ǿյ??׳?EmptyStackException
	 * 
	 * @return
	 */
	public Object poll() {
		Object obj = peek();
		stack.removeElementAt(0);
		changed = true;
		return obj;
	}

	/**
	 * ?鿴?׸?Ԫ?أ??????Ƴ??׸?Ԫ?أ?????????ǿյ??׳?EmptyStackException
	 * 
	 * @return
	 */
	public Object peek() {
		int len = size();
		if (len == 0) {
			throw new EmptyStackException();
		}
		return stack.elementAt(0);
	}

	/**
	 * ???ջ
	 */
	public void clear() {
		stack.clear();
		changed = true;
	}

	/**
	 * ????Ƿ??ջ
	 */
	public boolean empty() {
		return size() == 0;
	}

	/**
	 * ???ջ?Ƿ???
	 */
	public boolean isFull() {
		return size() == maxSize;
	}

	/**
	 * ת???ַ???
	 */
	public String toString() {
		int len = size();
		StringBuffer sb = new StringBuffer();
		for (int i = 0; i < len; i++) {
			sb.append(stack.elementAt(i)).append(';');
		}
		return sb.toString();
	}

}
 















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