add array stack

stack/AStack.java

@@ -0,0 +1,42 @@
+/** Array-based stack implementation */
+class AStack<E> implements Stack<E> {
+    private static final int defaultSize = 10;
+
+    private int maxSize; // Maximum size of stack
+    private int top; // Index for top Object
+    private E[] listArray; // Array holding stack
+
+    /** Constructors */
+    AStack() { this(defaultSize); }
+
+    @SuppressWarnings("unchecked") // Generic array allocation
+    AStack(int size) {
+	maxSize = size;
+	top = 0;
+	listArray = (E[])new Object[size]; // Create listArray
+    }
+
+    /** Reinitialize stack */
+    public void clear() { top = 0; }
+
+    /** Push "it" onto stack */
+    public void push(E it) {
+	assert top != maxSize : "Stack is full";
+	listArray[top++] = it;
+    }
+
+    /** Remove and pop element */
+    public E pop() {
+	assert top != 0 : "Stack is empty";
+	return listArray[--top];
+    }
+
+    /** @return Top element */
+    public E topValue() {
+	assert top != 0 : "Stack is empty";
+	return listArray[top - 1];
+    }
+
+    /** @return Stack size */
+    public int length() { return top; }
+}