package antlr.collections.impl;
/* ANTLR Translator Generator
* Project led by Terence Parr at http://www.jGuru.com
* Software rights: http://www.antlr.org/license.html
*
* $Id: //depot/code/org.antlr/release/antlr-2.7.5/antlr/collections/impl/LList.java#1 $
*/
import antlr.collections.List;
import antlr.collections.Stack;
import java.util.Enumeration;
import java.util.NoSuchElementException;
import antlr.collections.impl.LLCell;
/**A Linked List Implementation (not thread-safe for simplicity)
* (adds to the tail) (has an enumeration)
*/
public class LList implements List, Stack {
protected LLCell head = null, tail = null;
protected int length = 0;
/** Add an object to the end of the list.
* @param o the object to add
*/
public void add(Object o) {
append(o);
}
/** Append an object to the end of the list.
* @param o the object to append
*/
public void append(Object o) {
LLCell n = new LLCell(o);
if (length == 0) {
head = tail = n;
length = 1;
}
else {
tail.next = n;
tail = n;
length++;
}
}
/**Delete the object at the head of the list.
* @return the object found at the head of the list.
* @exception NoSuchElementException if the list is empty.
*/
protected Object deleteHead() throws NoSuchElementException {
if (head == null) throw new NoSuchElementException();
Object o = head.data;
head = head.next;
length--;
return o;
}
/**Get the ith element in the list.
* @param i the index (from 0) of the requested element.
* @return the object at index i
* NoSuchElementException is thrown if i out of range
*/
public Object elementAt(int i) throws NoSuchElementException {
int j = 0;
for (LLCell p = head; p != null; p = p.next) {
if (i == j) return p.data;
j++;
}
throw new NoSuchElementException();
}
/**Return an enumeration of the list elements */
public Enumeration elements() {
return new LLEnumeration(this);
}
/** How high is the stack? */
public int height() {
return length;
}
/** Answers whether or not an object is contained in the list
* @param o the object to test for inclusion.
* @return true if object is contained else false.
*/
public boolean includes(Object o) {
for (LLCell p = head; p != null; p = p.next) {
if (p.data.equals(o)) return true;
}
return false;
}
// The next two methods make LLQueues and LLStacks easier.
/** Insert an object at the head of the list.
* @param o the object to add
*/
protected void insertHead(Object o) {
LLCell c = head;
head = new LLCell(o);
head.next = c;
length++;
if (tail == null) tail = head;
}
/**Return the length of the list.*/
public int length() {
return length;
}
/** Pop the top element of the stack off.
* @return the top of stack that was popped off.
* @exception NoSuchElementException if the stack is empty.
*/
public Object pop() throws NoSuchElementException {
Object o = deleteHead();
return o;
}
// Satisfy the Stack interface now.
/** Push an object onto the stack.
* @param o the object to push
*/
public void push(Object o) {
insertHead(o);
}
public Object top() throws NoSuchElementException {
if (head == null) throw new NoSuchElementException();
return head.data;
}
}