queue&stack

Chapter1/Stack.java

@@ -0,0 +1,60 @@
+import java.util.Iterator;
+
+public class Stack<Item> implements Iterable<Item> {
+    private Node first;
+    private int N;
+
+    private class Node {
+        Item item;
+        Node next;
+    }
+
+    public void push(Item item) {
+        Node oldfirst = first;
+        first = new Node();
+        first.item = item;
+        first.next = oldfirst;
+        N++;
+    }
+
+    public Item pop() {
+        Item item = first.item;
+        first = first.next;
+        N--;
+        return item;
+    }
+
+    public Iterator<Item> iterator() {
+        return new ReverseArrayIterator();
+    }
+
+    private class ReverseArrayIterator implements Iterator<Item> {
+        private int i = N;
+
+        @Override
+        public boolean hasNext() {
+            return i > 0;
+        }
+
+        @Override
+        public Item next() {
+            Node nextnode = first;
+            for (int j = 0; j < N - i; j++)
+                nextnode = nextnode.next;
+            i--;
+            return nextnode.item;
+        }
+
+        public void remove() {
+        }
+    }
+
+    public static void main(String[] args) {
+        Stack<Integer> s = new Stack<Integer>();
+        s.push(1);
+        s.push(2);
+        s.push(3);
+        for (int i : s)
+            System.out.println(i);
+    }
+}