"NullPointerException" will be thrown when invoking method

This error occurs when a program attempts to use a reference variable that has a null value. When you try to invoke a method on such a variable, a NullPointerException will be thrown. To fix this error, you need to make sure that the reference variable is not null before invoking any method on it. You can use conditional statements or null checks to ensure that the variable is not null before using it.

相关问题

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference

This error occurs when you are trying to invoke the 'toString()' method on a null object reference. The 'toString()' method is used to convert an object to a string representation. However, if the object is null, then there is no object to convert and this error is thrown.

To fix this error, you need to make sure that the object you are calling the 'toString()' method on is not null. You can do this by checking for null before calling the method, like this:

if (object != null) {
String stringRepresentation = object.toString();
// Do something with the string representation
}

Alternatively, you can use the null-safe operator '?' to avoid a NullPointerException like this:

String stringRepresentation = object?.toString();