Adding in more Algorithms and Data Structures implemented in Java

src/Stack.java

@@ -0,0 +1,16 @@
+public interface Stack {
+    // Add to Top
+    void push(int item);
+    
+    // Remove from the top
+    int pop();
+    
+    // Look at the first item
+    int peek();
+    
+    // How many elements
+    int size();
+    
+    // Is the stack empty
+    boolean isEmpty();
+}