Error message: java.lang.NullPointerException - what to do?

The compiler checks the written program for everything except one: runtime exceptions. Such an exception is, for example, the NullPointerException, which belongs to the essential package java.lang in the Java programming language.

When does the compiler throw the java.lang.NullPointerException?

Exceptions often occur during the test phase. This applies in particular to the NullPointerException, which is usually encountered as a beginner when it comes to programming. More specifically, it is a variable that points to an empty object. For example, the error occurs in the following cases:

• When the element of an array is accessed and the element has no value.
• When querying the length of an array whose value is zero.
• If an object was created without the New operator and an attempt is made to perform operations with the reference variable.
• In our example, the remote control is practically the reference variable (pointer) that points to the real printer object. This variable is used to perform operations such as outputting error messages to the printer, calculating ink levels, etc. If the remote control points to an empty object or to no object, the reference variable has the value zero.

How to fix the error message

Exceptions can be caught under Java with a " try {...} catch {(Exception e)} " block. However, this method is not always necessary and also creates overhead. It is better to keep the following tips in mind:

• Check whether your object has been created. If this is not the case, create it using the command syntax " sample object name = new sample object (variables); ".
• With debug mode, you can check your code line by line and view intermediate results. Make sure that you do not overwrite your created object or save it with a NULL value. This means that the object is no longer available and further object commands trigger the error.
• Tip: If you change your object frequently, get used to checking your object before and after fundamental changes using an if query (" if (example object ! = NULL) {...} ").

In the next practical tip we will explain how you can use Lambda Expressions in Java.