Java实现Queue类
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Scanner; public class Queue<Item> implements Iterable<Item> {
private int N;
private Node<Item> first;
private Node<Item> last;
private static class Node<Item> {
private Item item;
private Node<Item> next;
}
public Queue() {
first = null;
last = null;
N = 0;
}
public boolean isEmpty() {
return first == null;
}
public int size() {
return N;
}
public Item peek() {
if(isEmpty()) throw new NoSuchElementException("Queue underflow");
return first.item;
}
public void enqueue(Item item) {
Node<Item> oldlast = last;
last = new Node<Item>();
last.item = item;
last.next = null;
if(isEmpty()) first = last;
else oldlast.next = last;
N ++;
}
public Item dequeue() {
if(isEmpty()) throw new NoSuchElementException("Queue underflow");
Item item = first.item;
first = first.next;
N --;
if(isEmpty()) last = null;
return item;
}
public String toString() {
StringBuilder s = new StringBuilder();
for(Item item : this)
s.append(item + " ");
return s.toString();
}
public Iterator<Item> iterator() {
return new ListIterator<Item>(first);
}
private class ListIterator<Item> implements Iterator<Item> {
private Node<Item> current; public ListIterator(Node<Item> first) {
current = first;
} public boolean hasNext() { return current != null; }
public void remove() { throw new UnsupportedOperationException(); } public Item next() {
if(!hasNext()) throw new NoSuchElementException();
Item item = current.item;
current = current.next;
return item;
}
} public static void main(String[] args) {
Queue<String> q = new Queue<String>();
Scanner in = new Scanner(System.in);
while(in.hasNext()) {
String item = in.next();
if(!item.equals("-")) q.enqueue(item);
else if(!q.isEmpty()) System.out.println(q.dequeue());
System.out.println("(" + q.size() + " left on queue)");
}
}
}