How to Properly Assign Final Variables in Java Constructors?

How do I correctly assign values to final variables within a Java constructor?

class MyClass {
    final int myFinalVariable;

    MyClass(int value) {
        myFinalVariable = value;
    }
}

In Java, final variables are constants that can only be assigned once. When initializing final variables in a constructor, it's essential to do so before any other operations in the class that might attempt to modify that variable. This guide discusses best practices to follow when dealing with final variable assignments within constructors.

class Example {
    final int constantValue;

    Example(int value) {
        this.constantValue = value; // Correct assignment for a final variable
    }
}

Causes

• Attempting to assign a final variable after its initial assignment leads to a compilation error.
• It's common to forget that final variables must be initialized during their declaration or within the constructor.

Solutions

• Ensure final variables are assigned during their declaration, or within the constructor before any other assignment.
• If multiple constructors exist, consider using constructor chaining to ensure proper initialization.

Mistake: Attempting to assign a final variable after constructor execution.

Solution: Always assign final variables in the constructor or during declaration.

Mistake: Not initializing final variables in all constructor overloads.

Solution: Use constructor chaining to ensure every constructor initializes final variables.