Design Pattern - Builder

 Builder 

Definition 

A builder pattern is a design pattern designed to provide a flexible solution to various object creation problems in object-oriented programming. The intent of the Builder design pattern is to separate the construction of a complex object from its representation. 

Advantages 

• Allows you to vary a product's internal representation 
• Encapsulates code for construction and representation 
• Provides control over steps of construction process 

Disadvantages 

• A distinct concrete builder must be created for each type of product
• May hamper dependency injection. 

Builder with code 

---

public class Car {

    private final Long id;
    private final String name;

    protected static class Builder {
        private Long id;
        private String name;

        public Builder id(Long id) {
            this.id = id;
            return this;
        }

        public Builder name(String name) {
            this.name = name;
            return this;
        }

        public Car build() {
            return new Car(this);
        }
    }

    private Car(Builder builder) {
        id = builder.id;
        name = builder.name;
    }

    public static Builder builder() {
        return new Builder();
    }

    public void runCar() {
        System.out.println("Car is running");
    }

}

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Now we can use the static Builder class inside the Car class. Let's make a car instance using Builder class and use the method runCar() to check if it is working. 

---

public class BuilderMain {

    public static void main(String[] args) {

        Car car = Car.builder()
                .id(1L)
                .name("Mustang")
                .build();

        car.runCar();
    }
}

---

And it seem's to work!! 

REFERENCE

https://en.wikipedia.org/wiki/Builder_pattern