What's wrong with overridable method calls in constructors?

The problem with overridable methods

Having overridable methods making a guest appearance in constructors is, to be honest, a recipe for disaster. You're stepping into territory with potential pitfalls that can spark elusive bugs due to the state's uninitialized nature. If the superclass constructor makes a call to an overridable method, it goes directly to the VIP room - the subclass's override, which might be innocently operating on fields yet to be initialized (because the subclass constructor hasn't had its turn). This clown fiesta can result in:

• Unpredictability: Think erratic behavior and corrupted states.
• Fragility: Super delicate code that breaks subtly when the class hierarchy evolves.
• Redundant Initializations: The second coming of overridden methods: those who call back into superclass methods, igniting unnecessary rounds of or looping initializations.

Design patterns as superheroes

Builder pattern is your hammer for complex initialization

For objects that have a complex personality and require a gradual and careful build-up, the builder pattern struts onto the stage. It severs the connection between object construction and its representation, resulting in flexible, readable, and maintainable code. It's the go-to tool when handling multiple parameters:

public class ComplexObject {
    private int param1;
    private String param2;

    private ComplexObject(Builder builder) {
        this.param1 = builder.param1;
        this.param2 = builder.param2;
    }

    // Joke: My builder is so static it jokes inner classes
    public static class Builder {
        private int param1;
        private String param2;

        public Builder param1(int val) {
            param1 = val;
            return this;
        }

        public Builder param2(String val) {
            param2 = val;
            return this;
        }

        public ComplexObject build() {
            // Validate params before building this beast
            return new ComplexObject(this);
        }
    }
}

// Joke: How to tell an object it's complex? Build it
ComplexObject obj = new ComplexObject.Builder()
                        .param1(123)
                        .param2("example")
                        .build();


Factory pattern for safe instance creation

The factory method pattern takes center stage to encapsulate the intricacies of instantiation logic. They can churn out instances of different subclasses based on specific criteria, ensuring that the sequence of operations follow the decorum.

public abstract class Product {
    // Product code ingredient list
}

public class ConcreteProductA extends Product {
    // Product A's secret recipe
}

public class ConcreteProductB extends Product {
    // Special sauce for Product B
}

public class ProductFactory {
    public static Product createProduct(String type) {
        if ("A".equals(type)) {
            return new ConcreteProductA(); // Product A, put the kettle on!
        } else if ("B".equals(type)) {
            return new ConcreteProductB(); // B for Brilliant!
        }
        throw new IllegalArgumentException("I haven't the foggiest idea what this product is!");
    }
}

// Finally decided on A? Good choice!
Product product = ProductFactory.createProduct("A");


Constructing with caution

Safety rules for constructors

To treat constructors with the respect they demand, here are some best practice tips:

1. Final methods only: Use these to complete the initialization ballet.
2. Private constructors: Pair these with factory methods.
3. Logical separation: Divide and conquer - one for constructor logic, one for initialization.
4. Lazy initialization: Consider delayed object creation.
5. Defensive copying: If mutable objects come knocking, make copies before you let them in.

Crafty constructor techniques

For those intricate initialization scenarios, you could rely on some crafty techniques:

• Instance-controlled classes: Use enums or other unique tactics to control instance creation.
• Immutable objects: They are low maintenance, needing no complicated constructor logic.
• Initialization blocks: Static or instance, they are readiness personified.

Visualization

What if constructing a building was a simultaneous act of laying the foundation (🏗️🔨) and drafting the blueprints for the upper floors (🏬🔝)? Messy, right?

Constructor (🏗️🔨):
1. Lay foundation
2. Build ground floor (Base class)
3. Construct upper floors (Overridable methods) - 🚧 Yikes!

Problem:
- Upper floors depend on the solid base 🏠💡
- If ground floor changes (base class), the top might not fit! 🏬 vs 🏚️

But don't fret! Approach with final methods or private constructors combined with static factory methods to uphold the Foundation First principle:

Safe Construction (🏗️👷‍♂️):
1. Cement foundation and ground floor (Final methods)
2. Build upper floors only after safety checks (Overridable methods post construction) 🏬✅