Factory Method

Provides an interface for creating objects in a superclass, but allows subclasses to alter the type of objects that will be created

The Factory Method is a creational design pattern that allows objects to be created without specifying the exact class of the object.

-> Allows multiple objects of different classes to be created

This is done by moving object initialisation inside a method, and using that method to get the object.

For example,

Changing

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class Thing {
  private int i;
  private int j;
  
  Thing(int a, int b) {
    i = a;
    j = b;
  }
}

//

new Thing(1,2);

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class Thing {
  private int i;
  private int j;
  
  private Thing(int a, int b) {
    i = a;
    j = b;
  }

  public static Thing create(int a, int b) {
    return new Thing(a, b);
  }
}

// 

Thing.create(1, 2)

This way, we could also make the create method abstract, allowing subclasses to fill in the functionality

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abstract class Thing {
  private int i;
  private int j;

  private Thing(int a, int b) {
    i = a;
    j = b;
  }

  // Static methods can't be abstract
  public abstract Thing create(int a, int b);
}

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