No Exception while type casting with a null in java

java nullpointerexception typecasting-operator
Vicky picture Vicky · Sep 10, 2013 · Viewed 148.5k times · Source 
String x = (String) null;

Why there is no exception in this statement?

String x = null;
System.out.println(x);

It prints null. But .toString() method should throw a null pointer exception.

Answer

Juned Ahsan picture Juned Ahsan · Sep 10, 2013

You can cast null to any reference type without getting any exception.

The println method does not throw null pointer because it first checks whether the object is null or not. If null then it simply prints the string "null". Otherwise it will call the toString method of that object.

Adding more details: Internally print methods call String.valueOf(object) method on the input object. And in valueOf method, this check helps to avoid null pointer exception:

return (obj == null) ? "null" : obj.toString();

For rest of your confusion, calling any method on a null object should throw a null pointer exception, if not a special case.

Related questions

What is a NullPointerException, and how do I fix it?

What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them? What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?

Read More
How to avoid null checking in Java?

I use object != null a lot to avoid NullPointerException. Is there a good alternative to this? For example I often use: if (someobject != null) { someobject.doCalc(); } This checks for a NullPointerException for the someobject object in the above snippet.

Read More
How to solve java.lang.NullPointerException error?

When I run my Java program, it gives me an error on this line compiler.getTask(null, null, new DiagnosticCollector<JavaFileObject>(), null, null, compilationUnits); Error I am getting is: Exception in thread "main" java.lang.NullPointerException at AnotherClassLoader.…

Read More