Developer Tech Blog

 When we programming with java, we can see 'java.lang.NullPointerException' error often. NullPointerException is kinds of RuntimeException.  This error occurs as a Java program attempts to use a null when an object is required. Let's see what this means.          Integer   invalid_intObject  =  null ;          System . out . println ( invalid_intObject . intValue ());  This codes makes NullPointerException because invalid_intObject is object but it's null. Below is valid code.            Integer   invalid_intObject  =  0 ;          System . out . println ( invalid_intObject . intValue ());  But in real programming world, this is not that simple to debug. So, what's in real programming world? we always call functions that we did not make...