ExceptionInInitializerError

Why This Happens

ExceptionInInitializerError wraps an exception thrown during class initialization. This includes static blocks, static field initializers, and enum constructors. The class becomes unusable after this error. Subsequent attempts to use the class will throw NoClassDefFoundError.

The Problem

public class Config {
    static final int PORT = Integer.parseInt(System.getenv("PORT")); // NPE if env var not set
    static {
        // Any exception here causes ExceptionInInitializerError
    }
}

The Fix

public class Config {
    static final int PORT;
    static {
        String portStr = System.getenv("PORT");
        PORT = (portStr != null) ? Integer.parseInt(portStr) : 8080;
    }
}

Step-by-Step Fix

1. 1

   Find the root cause

   Look at the 'Caused by' chain in the stack trace. The real exception is wrapped inside ExceptionInInitializerError.

2. 2

   Identify the static initializer

   Find the static block or static field initialization in the class that threw the exception.

3. 3

   Fix the initialization

   Add error handling in the static block, provide defaults for missing values, or move risky initialization to a method called lazily.