NullPointerException thrown when an calling methods on the object which is null.

It gives the line number on which exception is thrown at runtime.

Let’s see an example to reproduce the NullPointerException before java14 version.

package java14;

public class JavaNullTest {
    public static void main(String[] args) {
        Employee emp = new Employee();
        System.out.println(emp.department.name);
    }
}
class Employee {
    Department department;
    String name;
}

class Department {
    String name;
}

Outputs:

Exception in thread "main" java.lang.NullPointerException
 at HelloWorld.main(HelloWorld.java:7)

The above error is same for accessing property and method, assigning property on null object.

java14 NullPointerException enhancement

In Java14, It improves the error message display to an user.

It gives an following error while accessing the property on null object.

  • reading property on null object

emp.department.name throws below error as department is null. here you are reading the property on Null object. Exception in thread “main” java.lang.NullPointerException: Cannot read field “name” because “emp.department” is null at java14.JavaNullTest.main(JavaNullTest.java:6)

  • calling method on Null Object

let’s see an example to call method on null object

calling emp.department.getName() method, throws below error. Exception in thread “main” java.lang.NullPointerException: Cannot invoke “java14.Department.getName()” because “emp.department” is null at java14.Java14NullTest.main(Java14NullTest.java:6) Here department is null, and calling getName() method throws this error. department

package java14;

public class Java14NullTest {
    public static void main(String[] args) {
        Employee emp = new Employee();
        System.out.println(emp.department.getName());
    }
}
class Employee {
    Department department;
    String name;
}class Department {
    String name;
    String getName(){
        return name;
    }
}
  • Assign value to null object property

In this example, You are assigning string to an property of an null object and throws below error Exception in thread “main” java.lang.NullPointerException: Cannot assign field “name” because “emp.department” is null at java14.Java14NullTest.main(Java14NullTest.java:6)

here is an example

package java14;

public class Java14NullTest {
    public static void main(String[] args) {
        Employee emp = new Employee();
        emp.department.name="john";
    }
}
class Employee {
    Department department;
    String name;
}class Department {
    String name;
    String getName(){
        return name;
    }
}

This features is not enabled by default, You have to pass command line options -XX:+ShowCodeDetailsInExceptionMessages to display this type of errors at runtime.