What is NullPointerException example?

NullPointerException is a runtime exception and it is thrown when the application try to use an object reference which has a null value. For example, using a method on a null reference.

How do I fix NullPointerException?

NullPointerException is thrown when a reference variable is accessed (or de-referenced) and is not pointing to any object. This error can be resolved by using a try-catch block or an if-else condition to check if a reference variable is null before dereferencing it.

What is meant by NullPointerException?

NullPointerException is a RuntimeException. In Java, a special null value can be assigned to an object reference. NullPointerException is thrown when program attempts to use an object reference that has the null value. These can be: Invoking a method from a null object.

Why null is important?

It is used to signify missing or unknown values. The keyword NULL is used to indicate these values. NULL really isn’t a specific value as much as it is an indicator. Don’t think of NULL as similar to zero or blank, it isn’t the same.

How do you cause NullPointerException?

NullPointerException s are exceptions that occur when you try to use a reference that points to no location in memory (null) as though it were referencing an object. Calling a method on a null reference or trying to access a field of a null reference will trigger a NullPointerException .

Can we catch NullPointerException?

As stated already within another answer it is not recommended to catch a NullPointerException. However you definitely could catch it, like the following example shows. Although a NPE can be caught you definitely shouldn’t do that but fix the initial issue, which is the Check_Circular method.

What is an exception in coding?

Definition: An exception is an event, which occurs during the execution of a program, that disrupts the normal flow of the program’s instructions. When an error occurs within a method, the method creates an object and hands it off to the runtime system. This block of code is called an exception handler.

Why is NULL bad?

NULL exacerbates poor language decisions Java silently converts between reference and primitive types. Add in null, and things get even weirder. though it throws a NullPointerException when run. It’s bad enough that member methods can be called on null; it’s even worse when you never even see the method being called.

What does != NULL mean?

NULL is not a value. It is literally the absence of a value. You can’t “equal” NULL! The operator != does not mean “is not”; it means “is not equal to”.

How can you tell if an exception is checked or unchecked?

1. checked exception is checked by the compiler and as a programmer you have to handle it using try-catch-finally , throws.
2. unchecked exception is not checked by the compiler but you optionally can manage it explicitly.

What is the difference between checked and unchecked exception?

1) Checked: are the exceptions that are checked at compile time. If some code within a method throws a checked exception, then the method must either handle the exception or it must specify the exception using throws keyword. 2) Unchecked are the exceptions that are not checked at compiled time.

When is a null pointer exception thrown in Java?

Null Pointer Exception In Java NullPointerException is a RuntimeException. In Java, a special null value can be assigned to an object reference. NullPointerException is thrown when program attempts to use an object reference that has the null value.

Which is an example of a NullPointerException?

In below example, the person object is null and we are invoking its fields on null object leads to NullPointerException.

When to report a null pointer in Java?

So, it is important for Java beginners to take a basic course such as Java Fundamentals to avoid wasting time on such petty errors. Moreover, Java Null Pointer Exception is a Run time error. Instead, Null Pointer Exception occurrences in the code should actually be reported during the code compilation.

Why does synchronized throw NullPointerException in Java?

synchronized (mutex) will throw NullPointerException because “mutex” object is null. Sometimes we get an error page being sent as java web application response with error message as “HTTP Status 500 – Internal Server Error” and root cause as java.lang.NullPointerException.