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Lab105-VenbergGE/src/Stack.java

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+/**
+ * Data Structures & Algorithms 6th Edition 
+ * Goodrich, Tamassia, Goldwasser
+ * Code Fragment 6.1
+ * 
+ * An implementation of the stack interface
+ * */
+
+/**
+ * A collection of objects that are inserted and removed according to a last-in
+ * first-out principle. Although similar in purpose, this interface differs from
+ * java.util.stack.
+ * @author Gabriel Venberg
+ */
+public interface Stack<E> {
+    
+    /**
+     * returns the number of elements in the stack
+     * @return number of elements in the stack.
+     */
+    int size();
+    
+    /**
+     * tests whether the stack is empty.
+     * @return true if stack is empty, false otherwise.
+     */
+    boolean isEmpty();
+    
+    /**
+     * inserts an element at the top of the stack.
+     * @param e the element to be inserted.
+     */
+    void push(E e);
+    
+    /**
+     * returns, but does not remove, the top element of the stack.
+     * @return top element of the stack or null if empty.
+     */
+    E top();
+    
+    /**
+     * removes and returns the top element from the stack.
+     * @return element removed or null if empty.
+     */
+    E pop();
+}