diff --git a/group02/812350401/src/main/java/com/github/miniyk2012/coding2017/basic/stack/StackUtil.java b/group02/812350401/src/main/java/com/github/miniyk2012/coding2017/basic/stack/StackUtil.java
index 3b3dc501c7..c4e253d92b 100644
--- a/group02/812350401/src/main/java/com/github/miniyk2012/coding2017/basic/stack/StackUtil.java
+++ b/group02/812350401/src/main/java/com/github/miniyk2012/coding2017/basic/stack/StackUtil.java
@@ -52,7 +52,7 @@ public static void remove(Stack s,Object o) {
      */
     public static Object[] getTop(Stack s, int len) {
         if (len < 0) {
-            throw new IndexOutOfBoundsException();
+            return null;
         }
         Stack tempS = new Stack();
         while (tempS.size()<len && !s.isEmpty()) {
@@ -62,8 +62,11 @@ public static Object[] getTop(Stack s, int len) {
         Object[] o = new Object[actualLen];
         int i = actualLen;
         while (!tempS.isEmpty()) {
-            o[--i] = tempS.pop();
+            Object temp = tempS.pop();
+            o[--i] = temp;
+            s.push(temp);
         }
+
         return o;
     }
 
diff --git a/group02/812350401/src/test/java/com/github/miniyk2012/coding2017/basic/stack/StackUtilTest.java b/group02/812350401/src/test/java/com/github/miniyk2012/coding2017/basic/stack/StackUtilTest.java
index 25c6f27f00..62f3b3f281 100644
--- a/group02/812350401/src/test/java/com/github/miniyk2012/coding2017/basic/stack/StackUtilTest.java
+++ b/group02/812350401/src/test/java/com/github/miniyk2012/coding2017/basic/stack/StackUtilTest.java
@@ -2,7 +2,10 @@
 
 import org.junit.Test; 
 import org.junit.Before; 
-import org.junit.After; 
+import org.junit.After;
+import static junit.framework.TestCase.assertEquals;
+import static junit.framework.TestCase.assertNull;
+import static org.junit.Assert.assertArrayEquals;
 
 /** 
 * StackUtil Tester. 
@@ -10,66 +13,74 @@
 * @author <Authors name> 
 * @since <pre>Apr 6, 2017</pre> 
 * @version 1.0 
-*/ 
-public class StackUtilTest { 
+*/
+public class StackUtilTest {
 
-@Before
-public void before() throws Exception { 
-} 
+    private StackUtil sk;
+    @Before
+    public void setUp() throws Exception {
+    }
 
-@After
-public void after() throws Exception { 
-} 
+    @After
+    public void tearDown() throws Exception {
+    }
 
-/** 
-* 
-* Method: reverse(Stack s) 
-* 
-*/ 
-@Test
-public void testReverse() throws Exception { 
-//TODO: Test goes here... 
-} 
-
-/** 
-* 
-* Method: remove(Stack s, Object o) 
-* 
-*/ 
-@Test
-public void testRemove() throws Exception { 
-//TODO: Test goes here... 
-} 
-
-/** 
-* 
-* Method: getTop(Stack s, int len) 
-* 
-*/ 
-@Test
-public void testGetTop() throws Exception { 
-//TODO: Test goes here... 
-} 
+    @Test
+    public void testReverse() {
+        sk = new StackUtil();
+        Stack stack = new Stack();
+        stack.push(1);
+        stack.push(2);
+        stack.push(3);
+        sk.reverse(stack);
+        assertEquals(1, stack.pop());
+        assertEquals(2, stack.pop());
+        assertEquals(3, stack.pop());
+    }
+    @Test
+    public void testRemove() {
+        sk = new StackUtil();
+        Stack stack = new Stack();
+        stack.push(1);
+        stack.push(2);
+        stack.push(3);
+        stack.push(2);
+        stack.push(5);
+        sk.remove(stack, 2);
+        assertEquals(5, stack.pop());
+        assertEquals(3, stack.pop());
+        assertEquals(2, stack.pop());
+        assertEquals(1, stack.pop());
+    }
+    @Test
+    public void testGetTop() {
+        sk = new StackUtil();
+        Stack stack = new Stack();
 
-/** 
-* 
-* Method: isValidPairs(String s) 
-* 
-*/ 
-@Test
-public void testIsValidPairs() throws Exception { 
-//TODO: Test goes here... 
-} 
-
-/** 
-* 
-* Method: main(String[] args) 
-* 
-*/ 
-@Test
-public void testMain() throws Exception { 
-//TODO: Test goes here... 
-} 
+        Object[] array = sk.getTop(stack, 3);
+        assertArrayEquals(array, new Object[0]);
 
+        stack.push(1);
+        stack.push(2);
+        stack.push(3);
+        stack.push(2);
+        stack.push(5);
+        array = sk.getTop(stack, 3);
+        assertArrayEquals(array, new Object[] {5, 2, 3});
+        array = sk.getTop(stack, 6);
+        assertArrayEquals(new Object[] {5, 2, 3, 2, 1}, array);
+        array = sk.getTop(stack, -1);
+        assertNull(array);
+    }
+    @Test
+    public void testIsValidPairs() {
+        sk = new StackUtil();
+        String expr = "";
+        assertEquals(true, sk.isValidPairs(expr));
+        expr = "{xx[])yyza]}";
+        assertEquals(false, sk.isValidPairs(expr));
+        expr = "asd{[(asds)]sx}";
+        assertEquals(true, sk.isValidPairs(expr));
+    }
 
-} 
+}