listitem.java

JAVA 2入门经典 练习答案

// Chapter 6 Exercise 6

// Modified to support backwards traversal of the list.
// Additions and modifications are marked by ***

public class ListItem {
   ListItem next;             	// Refers to next item in the list.
   ListItem previous;         	// Refers to the previous item.       		***
   Object item;               	// The item for this ListItem.

   // Constructor: 
   public ListItem(Object item) {
    	this.item = item;        	// Store the item.
    	next = previous = null;  	// Set next and previous to null.	***
   }

   // Set the pointer to the next ListItem:
   public void setNext(ListItem next) {
    	this.next = next;        	// Store reference to the next item.
   }
  
   // Additional method to set the pointer to the previous ListItem:  		***
   public void setPrevious(ListItem previous) {                                                               
    	this.previous = previous; 	// Store reference to the previous item. 
   }
 

   // Get the next item in the list:
   public ListItem getNext() {
    	return next;
   }

   // Additional method to get the previous item in the list:         		***
   public ListItem getPrevious() {
     	return previous;
   }

   // Get the object for this item:
   public Object getObject() {
     	return item;
   }

   // Return class name & object:
   public String toString() {
    	return "ListItem " + item;
   }
}