Instance Factory Methods vs Static Factory Methods: Understanding the Differences

What are the differences between instance factory methods and static factory methods, and when should each be used?

Factory methods are design patterns that provide a way to create objects without specifying the exact class of the object that will be created. There are two main types of factory methods: instance factory methods and static factory methods. Understanding when to use each can significantly affect your code architecture, scalability, and performance.

class Product {
    private String name;
    
    private Product(String name) {
        this.name = name;
    }
    
    // Static factory method
    public static Product create(String name) {
        return new Product(name);
    }
}

class Factory {
    // Instance factory method
    public Product createProduct(String name) {
        return new Product(name);
    }
}

// Usage
Product product1 = Product.create("Static Product"); // Using static factory method
Factory factory = new Factory();
Product product2 = factory.createProduct("Instance Product"); // Using instance factory method

Causes

• Instance factory methods require an instance of the class to be created first before creating products.
• Static factory methods belong to the class itself and can be directly called without needing an instance.

Solutions

• Use instance factory methods when the creation of an object depends on instance-level data or state.
• Opt for static factory methods when the creation logic does not depend on instance data, providing more flexibility and easier testing.

Mistake: Confusing when to use an instance or static factory method.

Solution: Evaluate whether object creation relies on instance-specific data to determine the appropriate method.

Mistake: Overusing static factory methods leading to singleton-like patterns.

Solution: Ensure static factory methods generate new objects where applicable instead of reusing instances unnecessarily.