Java How to Program Fourth Edition - DCC

1102 Data Structures Chapter 19
146 return firstNode == null;
147 }
148
149 // output List contents
150 public synchronized void print()
151 {
152 if ( isEmpty() ) {
153 System.out.println( "Empty " + name );
154 return;
155 }
156
157 System.out.print( "The " + name + " is: " );
158
159 ListNode current = firstNode;
160
161 // while not at end of list, output current node's data
162 while ( current != null ) {
163 System.out.print( current.data.toString() + " " );
164 current = current.nextNode;
165 }
166
167 System.out.println( "\n" );
168 }
169
170 } // end class List
Fig. Fig. 19.3 19.3 Definitions of class ListNode and class List (part 4 of 4).
Class List contains private members firstNode (a reference to the first
ListNode in a List) and lastNode (a reference to the last ListNode in a List).
The constructors (lines 47–51 and 54–57) initialize both references to null. The most
important methods of class List are the synchronized methods insertAtFront
(lines 62–69), insertAtBack (lines 74–82), removeFromFront (lines 85–106) and
removeFromBack (lines 109–141). These methods are declared synchronized so
List objects can be multithread safe when used in a multithreaded program. If one thread
is modifying the contents of a List, no other thread can modify the same List object at
the same time. Method isEmpty (lines 144–147) is a predicate method that determines
whether the list is empty (i.e., the reference to the first node of the list is null). Predicate
methods typically test a condition and do not modify the object on which they are called. If
the list is empty, method isEmpty returns true; otherwise, it returns false. Method
print (lines 150–168) displays the list’s contents. Both isEmpty and print are also
synchronized methods.
1 // Fig. 19.4: EmptyListException.java
2 // Class EmptyListException definition
3 package com.deitel.jhtp4.ch19;
4
5 public class EmptyListException extends RuntimeException {
6
Fig. Fig. Fig. 19.4 19.4 Definition of class EmptyListException (part 1 of 2).