Exception in thread main java.lang.NullPointerException in Java

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Want to fix exception in thread main java.lang.NullPointerException? Java.lang.NullPointerException is one of the most common exceptions in java programming. Anyone working on Java must have seen this exception for sure.

The NullPointerException exception is a runtime exception, so we can not catch it and even it is not needed. The NullPointerException exception is displayed in the application when we try to do some null operations when an object needed is empty or does not hold any value, not even a reference.

When does a NullPointerException occur in Java?

Javadoc from java.lang.NullPointerException has explained the scenario where it can occur:
  1. When the method instance is called on a null object.
  2. When accessing or modifying variables or fields in null objects.
  3. When the matrix length is called when the array is ​​null.
  4. Access or modify the null slot as a array.
  5. When trying to synchronize with null objects or use null values in blocks synchronized on Java, see Core Java for more details.

Reasons behind java.lang.NullPointerException

Some common reasons for NullPointerException in java programs are:
  1. Request methods in object instances, but at runtime the object is null.
  2. Access variables from null object instances at runtime.
  3. Throw null in the program.
  4. Access index or change the null table index value
  5. Check the null array length at run time.

How to find exception java.lang.NullPointerException

NullPointerException is very easy to find, just look at trace and find out which Class has got the nullpointer exceptions. You should see a line number in front of the class name. Next, look at the code and exact line and check which object can be null, which causes a NullPointerException exception.

How to fix java.lang.NullPointerException

Java.lang.NullPointerException is an exception that is not handled, so it does not need to be detected. In general, it is possible to prevent null pointer exceptions using zero controls and preventive coding techniques. See the sample code below that shows how to fix exception in thread main java.lang.NullPointerException .
exception in thread main java.lang.nullpointerexception
Try to add checks before accessing varibales.

String msg = (str == null) ? "" : str.substring(0, str.length()-1);
In addition to this you always need to use if checks to check for nulls. This is the best coding practice.

if(object != null) { object.toString(); }

NullPointerException is RuntimeException. In Java, null values ​​can be given for object references. The NullPointerException exception occurs when an application tries to use a reference object whose value is null. This includes:
  1. Call the instance method on the object referenced by null reference.
  2. Access or change the example field of an object referenced by null references.
  3. If the reference type is a table type, take the null reference length.
  4. If the reference type is a table type, access or modification of the null reference slot.
  5. If the reference type is a Throwable subtype, give null references.
The application must delete this class instance to show the use of null other illegal objects. Read more about NullPointerException at Oracle Docs.

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