part 1 and 2

src/main/java/Pair/Arrays.java

@@ -11,6 +11,6 @@ import java.util.Collections;
  * And a minmax method that returns a pair containing the largest and smallest items from the array list
  */
 public class Arrays {
-    public static <___> Pair<E> firstLast(ArrayList<___> a) {
-    }
+//    public static <___> Pair<E> firstLast(ArrayList<___> a) {
+//    }
 }

src/main/java/StackArray/GenericStack.java

@@ -1,5 +1,4 @@
 package StackArray;
-
 import java.util.Arrays;
 
 /**
@@ -11,5 +10,25 @@ public class GenericStack<E> {
     private E[] elements;
 
     public GenericStack() {
+        elements = (E[]) new Object[0];
+    }
+
+    public boolean isEmpty() {
+        return elements.length == 0;
+    }
+
+    public void push(E element) {
+        elements = Arrays.copyOf(elements, elements.length+1);
+        elements[elements.length-1] = element;
+    }
+
+    public E pop() throws IndexOutOfBoundsException {
+        if (isEmpty()) {
+            throw new IndexOutOfBoundsException();
+        } else {
+            E elementToPop = elements[elements.length-1];
+            elements = Arrays.copyOf(elements, elements.length-1);
+            return elementToPop;
+        }
     }
 }

src/main/java/StackArray/ObjectStack.java

@@ -11,6 +11,25 @@ public class ObjectStack<E> {
     private Object[] elements;
 
     public ObjectStack() {
+        elements = new Object[0];
+    }
+
+    public boolean isEmpty() {
+        return elements.length == 0;
+    }
+
+    public void push(Object element) {
+        elements = Arrays.copyOf(elements, elements.length+1);
+        elements[elements.length-1] = element;
+    }
 
+    public Object pop() throws IndexOutOfBoundsException {
+        if (isEmpty()) {
+            throw new IndexOutOfBoundsException();
+        } else {
+            Object elementToPop = elements[elements.length-1];
+            elements = Arrays.copyOf(elements, elements.length-1);
+            return elementToPop;
+        }
     }
 }

src/main/java/StackArrayList/Stack.java

@@ -7,10 +7,26 @@ import java.util.ArrayList;
  * If you pop on an empty stack, throw an IndexOutOfBoundsException.
  */
 public class Stack<E> {
-    private ArrayList elements;
+    private ArrayList<E> elements;
 
 
     public Stack(){
+        elements = new ArrayList<E>();
+    }
+
+    public boolean isEmpty() {
+        return elements.size() == 0;
+    }
+
+    public void push(E element) {
+        elements.add(element);
+    }
 
+    public E pop() throws IndexOutOfBoundsException {
+        if (isEmpty()) {
+            throw new IndexOutOfBoundsException();
+        } else {
+            return elements.remove(elements.size() - 1);
+        }
     }
 }

src/test/java/StackArray/GenericStackTest.java

@@ -1,41 +1,41 @@
-//package StackArray;
-//
-//import org.junit.Assert;
-//import org.junit.Test;
-//
-//public class GenericStackTest {
-//    @Test
-//    public void testPushingGrowsTheStack() throws Exception {
-//        // Given an empty stack
-//        GenericStack<String> stack = new GenericStack<>();
-//
-//        // Assert that it is empty.
-//        Assert.assertEquals(true, stack.isEmpty());
-//        // When we push something onto the stack
-//        stack.push("foobar");
-//        // Then it shouldn't be empty
-//        Assert.assertEquals(false, stack.isEmpty());
-//    }
-//
-//    @Test
-//    public void testPushingAndPoppingOrder() throws Exception {
-//        // Given an empty stack
-//        GenericStack<String> stack = new GenericStack<>();
-//        // When we push two elements on it
-//        stack.push("foo");
-//        stack.push("bar");
-//        // Then we should see them returned in the correct order
-//        Assert.assertEquals("bar", stack.pop());
-//        Assert.assertEquals("foo", stack.pop());
-//    }
-//
-//    @Test(expected = IndexOutOfBoundsException.class)
-//    public void testPopFirst() throws Exception {
-//        // Given an empty stack
-//        GenericStack<String> stack = new GenericStack<>();
-//        // When it's popped
-//        stack.pop();
-//        // Then we should get an exception
-//    }
-//
-//}
+package StackArray;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class GenericStackTest {
+    @Test
+    public void testPushingGrowsTheStack() throws Exception {
+        // Given an empty stack
+        GenericStack<String> stack = new GenericStack<>();
+
+        // Assert that it is empty.
+        Assert.assertEquals(true, stack.isEmpty());
+        // When we push something onto the stack
+        stack.push("foobar");
+        // Then it shouldn't be empty
+        Assert.assertEquals(false, stack.isEmpty());
+    }
+
+    @Test
+    public void testPushingAndPoppingOrder() throws Exception {
+        // Given an empty stack
+        GenericStack<String> stack = new GenericStack<>();
+        // When we push two elements on it
+        stack.push("foo");
+        stack.push("bar");
+        // Then we should see them returned in the correct order
+        Assert.assertEquals("bar", stack.pop());
+        Assert.assertEquals("foo", stack.pop());
+    }
+
+    @Test(expected = IndexOutOfBoundsException.class)
+    public void testPopFirst() throws Exception {
+        // Given an empty stack
+        GenericStack<String> stack = new GenericStack<>();
+        // When it's popped
+        stack.pop();
+        // Then we should get an exception
+    }
+
+}

src/test/java/StackArray/ObjectStackTest.java

@@ -1,39 +1,39 @@
-//package StackArray;
-//
-//import org.junit.Assert;
-//import org.junit.Test;
-//
-//public class ObjectStackTest {
-//    @Test
-//    public void testPushingGrowsTheStack() throws Exception {
-//        // Given an empty stack
-//        ObjectStack<String> stack = new ObjectStack<>();
-//        // Assert that it is empty.
-//        Assert.assertEquals(true, stack.isEmpty());
-//        // When we push something onto the stack
-//        stack.push("foobar");
-//        // Then it shouldn't be empty
-//        Assert.assertEquals(false, stack.isEmpty());
-//    }
-//
-//    @Test
-//    public void testPushingAndPoppingOrder() throws Exception {
-//        // Given an empty stack
-//        ObjectStack<String> stack = new ObjectStack<>();
-//        // When we push two elements on it
-//        stack.push("foo");
-//        stack.push("bar");
-//        // Then we should see them returned in the correct order
-//        Assert.assertEquals("bar", stack.pop());
-//        Assert.assertEquals("foo", stack.pop());
-//    }
-//
-//    @Test(expected = IndexOutOfBoundsException.class)
-//    public void testPopFirst() throws Exception {
-//        // Given an empty stack
-//        ObjectStack<String> stack = new ObjectStack<>();
-//        // When it's popped
-//        stack.pop();
-//        // Then we should get an exception
-//    }
-//}
+package StackArray;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class ObjectStackTest {
+    @Test
+    public void testPushingGrowsTheStack() throws Exception {
+        // Given an empty stack
+        ObjectStack<String> stack = new ObjectStack<>();
+        // Assert that it is empty.
+        Assert.assertEquals(true, stack.isEmpty());
+        // When we push something onto the stack
+        stack.push("foobar");
+        // Then it shouldn't be empty
+        Assert.assertEquals(false, stack.isEmpty());
+    }
+
+    @Test
+    public void testPushingAndPoppingOrder() throws Exception {
+        // Given an empty stack
+        ObjectStack<String> stack = new ObjectStack<>();
+        // When we push two elements on it
+        stack.push("foo");
+        stack.push("bar");
+        // Then we should see them returned in the correct order
+        Assert.assertEquals("bar", stack.pop());
+        Assert.assertEquals("foo", stack.pop());
+    }
+
+    @Test(expected = IndexOutOfBoundsException.class)
+    public void testPopFirst() throws Exception {
+        // Given an empty stack
+        ObjectStack<String> stack = new ObjectStack<>();
+        // When it's popped
+        stack.pop();
+        // Then we should get an exception
+    }
+}

src/test/java/StackArrayList/StackTest.java

@@ -1,45 +1,45 @@
-//package StackArrayList;
-//
-//import org.junit.Test;
-//
-//import org.junit.Assert;
-//
-//public class StackTest {
-//    @Test
-//    public void testEmptyStackStopsBeingEmptyWhenAnItemIsAdded() throws Exception {
-//        // Given an empty stack
-//        Stack<String> stack = new Stack<>();
-//        // Assert that it starts empty
-//        Assert.assertEquals(true, stack.isEmpty());
-//        // When an element gets pushed
-//        stack.push("foobar");
-//        // Then the stack should not be empty.
-//        Assert.assertEquals(false, stack.isEmpty());
-//    }
-//
-//    @Test
-//    public void testTwoItemsPushedComeOutInCorrectOrder() throws Exception {
-//        // Given an empty stack
-//        Stack<String> stack = new Stack<>();
-//
-//        //When two items are pushed
-//        stack.push("foo");
-//        stack.push("bar");
-//
-//        // Then they should come off in reverse order.
-//        Assert.assertEquals("bar", stack.pop());
-//        Assert.assertEquals("foo", stack.pop());
-//
-//        // And then the stack should be empty
-//        Assert.assertEquals(true, stack.isEmpty());
-//    }
-//
-//    @Test(expected = IndexOutOfBoundsException.class)
-//    public void testPopFirst() throws Exception {
-//        // Given an empty stack
-//        Stack<String> stack = new Stack<>();
-//        // Then it is popped
-//        stack.pop();
-//        // We should get an exception
-//    }
-//}
+package StackArrayList;
+
+import org.junit.Test;
+
+import org.junit.Assert;
+
+public class StackTest {
+    @Test
+    public void testEmptyStackStopsBeingEmptyWhenAnItemIsAdded() throws Exception {
+        // Given an empty stack
+        Stack<String> stack = new Stack<>();
+        // Assert that it starts empty
+        Assert.assertEquals(true, stack.isEmpty());
+        // When an element gets pushed
+        stack.push("foobar");
+        // Then the stack should not be empty.
+        Assert.assertEquals(false, stack.isEmpty());
+    }
+
+    @Test
+    public void testTwoItemsPushedComeOutInCorrectOrder() throws Exception {
+        // Given an empty stack
+        Stack<String> stack = new Stack<>();
+
+        //When two items are pushed
+        stack.push("foo");
+        stack.push("bar");
+
+        // Then they should come off in reverse order.
+        Assert.assertEquals("bar", stack.pop());
+        Assert.assertEquals("foo", stack.pop());
+
+        // And then the stack should be empty
+        Assert.assertEquals(true, stack.isEmpty());
+    }
+
+    @Test(expected = IndexOutOfBoundsException.class)
+    public void testPopFirst() throws Exception {
+        // Given an empty stack
+        Stack<String> stack = new Stack<>();
+        // Then it is popped
+        stack.pop();
+        // We should get an exception
+    }
+}