QueueEmpty.java

package ca.ubc.cs.spl.aspectPatterns.examples.state.java;

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 * 
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/**
 * Implements the <i>ConcreteState</i> "empty" for the queue example. 
 * Removing items is impossible if the queue is empty. Inserting items will
 * trigger a state change to "normal".
 *
 * @author  Jan Hannemann
 * @author  Gregor Kiczales
 * @version 1.1, 02/17/04
 *        
 * @see QueueNormal
 * @see QueueFull
 */

public class QueueEmpty implements QueueState {
	
    /**
     * Tries to insert an object into the queue. Returns true if successful, 
     * false otherwiese. The state of the context
     * is changed to "normal" (queue is no longer empty).
     *
     * @param context the <i>Context</i> for this design pattern (for update 
     * on demand)
     * @param arg the object to be inserted into the queue
     * @return true if insertion was successful, false otherwise.
     */ 
	
	public boolean insert(QueueContext context, Object arg) {
		QueueNormal nextState = new QueueNormal(); 
		context.setState(nextState);
		return nextState.insert(context, arg); 
	}

    /**
     * Returns the first item in the queue. Returns null since the queue is 
     * empty.
     *
     * @param context the <i>Context</i> for this design pattern (for update 
     * on demand)
     * @return null.
     */ 

	public Object  getFirst(QueueContext context) {
		return null;
	}

    /**
     * Tries to remove an object from the queue. Returns false (queue is 
     * empty).
     *
     * @param context the <i>Context</i> for this design pattern (for update 
     * on demand)
     * @return false.
     */ 

	public boolean removeFirst(QueueContext context){
		return false;
	} 

}