Why Does a Static Variable Initialized by a Method Call Sometimes Return Null?

Why does a static variable initialized by a method call that returns another static variable remain null?

class Example {
    static Integer staticVar;
    
    public static Integer getStaticVar() {
        return staticVar;
    }
    
    public static void initialize() {
        staticVar = getStaticVar(); // This can result in staticVar being null
    }
}

Static variables in programming often hold their values throughout the lifespan of an application. However, when they are initialized through method calls, especially if those methods reference themselves or other static variables, they can potentially return null if not properly configured.

class Example {
    static Integer staticVar = initialize(); 
    
    static Integer initialize() {
        return 10;  // Correctly initializes staticVar
    }
}

Causes

• The static variable being referenced has not been initialized before the method call is made.
• The method invoked does not set the static variable, or it returns a value that has not been assigned.
• Field initialization order can cause references to static variables to be null if those variables are accessed before they are assigned.

Solutions

• Ensure that the static variable is properly initialized before being referenced in the method call.
• Refactor the method to assign a value directly to the static variable if its intended behavior is to preset a value.
• Utilize constructors or initializers to properly set static fields in the correct order.

Mistake: Assuming static variables are automatically initialized; they need explicit initialization.

Solution: Always initialize your static variables explicitly for predictable behavior.

Mistake: Accessing a static variable before it has been assigned a value.

Solution: Rearrange your code to ensure all static fields are initialized before being accessed.