Linked List example
/*
* Copyright (c) 2000 David Flanagan. All rights reserved.
* This code is from the book Java Examples in a Nutshell, 2nd Edition.
* It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
* You may study, use, and modify it for any non-commercial purpose.
* You may distribute it non-commercially as long as you retain this notice.
* For a commercial use license, or to purchase the book (recommended),
* visit http://www.davidflanagan.com/javaexamples2.
*/
/**
* This class implements a linked list that can contain any type of object that
* implements the nested Linkable interface. Note that the methods are all
* synchronized, so that it can safely be used by multiple threads at the same
* time.
*/
public class LinkedList {
/**
* This interface defines the methods required by any object that can be
* linked into a linked list.
*/
public interface Linkable {
public Linkable getNext(); // Returns the next element in the list
public void setNext(Linkable node); // Sets the next element in the list
}
// This class has a default constructor: public LinkedList() {}
/** This is the only field of the class. It holds the head of the list */
Linkable head;
/** Return the first node in the list */
public synchronized Linkable getHead() {
return head;
}
/** Insert a node at the beginning of the list */
public synchronized void insertAtHead(Linkable node) {
node.setNext(head);
head = node;
}
/** Insert a node at the end of the list */
public synchronized void insertAtTail(Linkable node) {
if (head == null)
head = node;
else {
Linkable p, q;
for (p = head; (q = p.getNext()) != null; p = q)
/* no body */;
p.setNext(node);
}
}
/** Remove and return the node at the head of the list */
public synchronized Linkable removeFromHead() {
Linkable node = head;
if (node != null) {
head = node.getNext();
node.setNext(null);
}
return node;
}
/** Remove and return the node at the end of the list */
public synchronized Linkable removeFromTail() {
if (head == null)
return null;
Linkable p = head, q = null, next = head.getNext();
if (next == null) {
head = null;
return p;
}
while ((next = p.getNext()) != null) {
q = p;
p = next;
}
q.setNext(null);
return p;
}
/**
* Remove a node matching the specified node from the list. Use equals()
* instead of == to test for a matched node.
*/
public synchronized void remove(Linkable node) {
if (head == null)
return;
if (node.equals(head)) {
head = head.getNext();
return;
}
Linkable p = head, q = null;
while ((q = p.getNext()) != null) {
if (node.equals(q)) {
p.setNext(q.getNext());
return;
}
p = q;
}
}
/**
* This is a test class that implements the Linkable interface
*/
static class LinkableInteger implements Linkable {
int i; // The data contained in the node
Linkable next; // A reference to the next node in the list
public LinkableInteger(int i) {
this.i = i;
} // Constructor
public Linkable getNext() {
return next;
} // Part of Linkable
public void setNext(Linkable node) {
next = node;
} // Linkable
public String toString() {
return i + "";
} // For easy printing
public boolean equals(Object o) { // For comparison
if (this == o)
return true;
if (!(o instanceof LinkableInteger))
return false;
if (((LinkableInteger) o).i == this.i)
return true;
return false;
}
}
/**
* The test program. Insert some nodes, remove some nodes, then print
* out all elements in the list. It should print out the numbers 4, 6,
* 3, 1, and 5
*/
public static void main(String[] args) {
LinkedList ll = new LinkedList(); // Create a list
ll.insertAtHead(new LinkableInteger(1)); // Insert some stuff
ll.insertAtHead(new LinkableInteger(2));
ll.insertAtHead(new LinkableInteger(3));
ll.insertAtHead(new LinkableInteger(4));
ll.insertAtTail(new LinkableInteger(5));
ll.insertAtTail(new LinkableInteger(6));
System.out.println(ll.removeFromHead()); // Remove and print a node
System.out.println(ll.removeFromTail()); // Remove and print again
ll.remove(new LinkableInteger(2)); // Remove another one
// Now print out the contents of the list.
for (Linkable l = ll.getHead(); l != null; l = l.getNext())
System.out.println(l);
}
}
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