How to Fix ExceptionInInitializer Error in Java

1. Brief Introduction to ExceptionInInitializerError in Java
2. Handle the ExceptionInInitializerError in Java
3. Conclusion

In this article, we will learn about the ExceptionInInitializerError in Java.

Brief Introduction to ExceptionInInitializerError in Java

ExceptionInInitializerError is an unchecked exception in Java, and it’s the child of the Error class. It falls in the category of Runtime Exceptions.

In Java, whenever the JVM (Java Virtual Machine) fails to evaluate a static initializer block or instantiate or assign a value to a static variable, an exception ExceptionInInitializerError occurs. This indicates that something has gone wrong in the static initializer.

Whenever this exception occurs inside the static initializer, Java maintains the reference to the actual exception as the root cause by wrapping the exception inside the object of the ExceptionInInitializerError class.

Examples of ExceptionInInitializerError in Java

Based on the above discussion, ExceptionInInitializerError occurs in major cases. Let’s see some examples to understand it better.

Example 1: Scenario where we are assigning values to the static variable.

public class Test {
  static int x = 100 / 0;
  public static void main(String[] args) {
    System.out.println("Value of x is " + x);
  }
}

Output:

Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: java.lang.ArithmeticException: / by zero
    at Test.<clinit>(Test.java:4)

In the above code, we assigned a 100/0 value to a static variable x, which gives an undefined arithmetic behavior, so an exception occurs while assigning values to the static variable, which finally gives us the ExceptionInInitializerError.

We can also observe in the output that the actual exception ArithmeticException is wrapped inside an instance of the ExceptionInInitializerError class.

Example 2: Scenario where inside the static blocks, null values are assigned.

public class Test {
  static {
    String str = null;
    System.out.println(str.length());
  }

  public static void main(String[] args) {}
}

Output:

Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: java.lang.NullPointerException: Cannot invoke "String.length()" because "str" is null
    at Test.<clinit>(Test.java:7)

In the above code, we have created a static block inside which we have a string str with the null value. So, when we try to get its length using the length() method, we get NullPointerException as we print the length of a string with null as its value.

But, as this exception occurs inside a static block, it will be wrapped inside the ExceptionInInitializerError class, and we get ExceptionInInitializerError in the output.

Handle the ExceptionInInitializerError in Java

ExceptionInInitializerError in Java can be avoided by ensuring the following points:

1. Make sure that initializing static variables in a program doesn’t throw any Runtime Exception.
2. Make sure that the static initializer blocks in a program don’t throw any Runtime Exception.

Conclusion

In this article, we learned about ExceptionInInitializerError in Java, indicating that some exceptions occurred while initializing a static variable or evaluating a static block. This error works as a runtime wrapper for the underlying exception and stops the JVM until the programmer resolves the underlying exception.