list.java

j2se程序

package com.deitel.jhtp5.ch20;

// class to represent one node in a list
class ListNode{
	
	// package access members; List can access these directly
	Object data;
	int[] information = new int[5];
	ListNode nextNode;
	
	// create a LisNode that refrs to object
	ListNode( Object object , int[] info )
	{
		data = object;
		nextNode = null;
		for( int i = 0; i<=4; i++ )
			information[i] = info[i];
	}
	
	// create ListNode that refers to Object and to next ListNode
	ListNode( Object object, ListNode node, int[] info )
	{
		data = object;
		nextNode = node;
		for( int i = 0 ; i<=4 ; i++ )
			information[i] = info[i];
	}
	
	// return reference to data in node
	Object getObject()
	{
		return data; // retrun object in this node	
	}
	
	int[] getInfo()
	{
		return information;	
	}
	
	// return reference to next node in list
	ListNode getNext()
	{
		return nextNode; // get next node	
	}
} // end of ListNode

public class List{
	private ListNode firstNode;
	private ListNode lastNode;
	private String name; // string like "list" used in printing
	
	// construct empty List with "list" as the name
	public List()
	{
		this( "list" )	;
	}
	
	// construct an empty List with a name
	public List( String listName )
	{
		name = listName;
		firstNode = lastNode = null;	
	}
	
	// insert Object at front of List
	public synchronized void insertAtFront( Object insertItem, int[] info )
	{
		if ( isEmpty() ) // firstNode and lastNode refer to same object
			firstNode = lastNode = new ListNode( insertItem, info );
			
		else // firstNode refers to new node
			firstNode = new ListNode( insertItem, firstNode, info );
	}
	
	// insert Object at end of List
	public synchronized void insertAtBack( Object insertItem, int[] info )
	{
		if ( isEmpty() ) // firstNode and lastNode refer to same object
			firstNode = lastNode = new ListNode( insertItem, info );
			
		else // lastNode's nextNode refers to new node
			lastNode = lastNode.nextNode = new ListNode( insertItem, info );
	}
	
	//remove first node from List
	public synchronized int[] removeFromFront() throws EmptyListException
	{
		if ( isEmpty() ) // throw exception if List is empty
			throw new EmptyListException( name );
		
		int[] removedItem = firstNode.getInfo(); // retrieve data being removed
		
		// update references firstNode and lastNode
		if( firstNode == lastNode )
			firstNode = lastNode = null;
		else
			firstNode = firstNode.nextNode;
		
		return removedItem; // retrun removed node data
	} // end method removeFromFront
	
	//remove last node from List
	public synchronized Object removeFromBack() throws EmptyListException
	{
		if ( isEmpty() ) // throw exception if List is empty
			throw new EmptyListException( name );
		
		Object removedItem = lastNode.data; // retrieve data being removed
		
		// update references firstNode and lastNode
		if ( firstNode == lastNode )
			firstNode = lastNode = null;
		else{ // locate new last node
			ListNode current = firstNode;
			
			//loop while current node !-> lastnode
			while( current.nextNode != lastNode )
				current = current.nextNode;
			
			lastNode = current; // current is new lastNode
			current.nextNode = null;
		}
		
		return removedItem; // return removed node data

	} // end method removeFromBack
	
	// determine whether list is empty
	public synchronized boolean isEmpty()
	{
		return firstNode == null; // return true if list is empty
	}
	
	// output List contents
	public synchronized void print()
	{
		if ( isEmpty() ){
			System.out.println( "Empty " + name );
			return;
		}
		
		System.out.print( "The " + name + " is: " );
		ListNode current = firstNode;
		
		// while not at end of list, output current node's data
		while ( current != null ){
			for( int i=0; i<=4; i++ ) System.out.print( current.information[i] + " " );
			System.out.println( "\n" );
			current = current.nextNode;
		}
		
		System.out.println( "\n" );
	}
	
	public synchronized int[] getInfo()
	{
		if ( isEmpty() ){
			System.out.println( "Empty " + name );
			return null;
		}
		
		return lastNode.getInfo();
	}
	public synchronized Object getName()
	{
		if ( isEmpty() ){
			System.out.println( "Empty " + name );
			return null;
		}
		return firstNode.getObject();	
	}
} // end class List