From 9fd420a9af3d5c21a0cfb0010275fe26b2ca87e6 Mon Sep 17 00:00:00 2001
From: Isak Rabin <isak.rabin@mail.rakuten.com>
Date: Wed, 31 Oct 2018 14:50:59 +0900
Subject: [PATCH] Add check to avoid null pointer exception

---
 java/Chapter 3/Question3_3/Question.java    | 4 +++-
 java/Chapter 3/Question3_3/SetOfStacks.java | 3 +++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/java/Chapter 3/Question3_3/Question.java b/java/Chapter 3/Question3_3/Question.java
index 18acfe5d..5ae3b602 100644
--- a/java/Chapter 3/Question3_3/Question.java	
+++ b/java/Chapter 3/Question3_3/Question.java	
@@ -8,7 +8,9 @@ public static void main(String[] args) {
 			set.push(i);
 		}
 		for (int i = 0; i < 34; i++) {
-			System.out.println("Popped " + set.pop());
+            if (!set.isEmpty()) {
+                System.out.println("Popped " + set.pop());
+            }
 		}		
 	}
 }
diff --git a/java/Chapter 3/Question3_3/SetOfStacks.java b/java/Chapter 3/Question3_3/SetOfStacks.java
index 8e3cc0e0..fda9c8cc 100644
--- a/java/Chapter 3/Question3_3/SetOfStacks.java	
+++ b/java/Chapter 3/Question3_3/SetOfStacks.java	
@@ -30,6 +30,9 @@ public void push(int v) {
 	
 	public int pop() {
 		Stack last = getLastStack();
+        if (last==null){
+            throw new Exception("Stack is empty - No more element is available");
+        }        
 		int v = last.pop();
 		if (last.size == 0) {
 			stacks.remove(stacks.size() - 1);