Why do I have a NullPointerException?

What is a NullPointerException?

• Answer:

  A NullPointerException is an exception thrown by the Java Virtual Machine when you try to access a variable as if it were an object when it is contains null. For example, the following code would throw a NullPointerException: String s; if (s.charAt(0) == 'c') // this line throws NullPointerException return "s[0] is 'c'";