Better BuilderPattern

1 - README.md

A Better Builder Pattern

The Builder pattern came up during a recent PR while looking at the standard Getter/Setter POJO pattern. I usually avoided the classic Builder pattern based on the necessity to duplicate the member variables in the static inner Builder class.

After some Googling and discussion we decided to use a slightly different Builder pattern. In this version the base object is instantiated in the Builder constructor and simply returned (and discarded) from the build() function. This pattern allows for efficiently creating an immutable object while eliminating one of my pet peeves of duplicate code!

Here's an implementation where the Builder pattern is encapsulated in a BaseBuilder class.

2 - BaseBuilder.java

public abstract class BaseBuilder<T> {
    protected T data;

    /**
     * Constructor that accepts instantiated data object.
     * @param data
     */
    public BaseBuilder(T data) {
        this.data = data;
    }

    /**
     * Pass back the built up object and prevent class from modifying it further
     * @return
     */
    public T build() {
        T value = data;
        // discard built data object
        data = null;
        return value;
    }
}

3 - User.java

public class User {
    private final String firstName;
    private final String lastName;

    private String state;
    private String country;

    private User(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    public String getFirstName() {
        return firstName;
    }

    public String getLastName() {
        return lastName;
    }

    public String getState() {
        return state;
    }

    public String getCountry() {
        return country;
    }

    public static class Builder extends BaseBuilder<User> {

        public Builder(final String firstName, final String lastName) {
            super(new User(firstName, lastName));
        }

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

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

4 - MainApplication.java

public class MainApplication {
    public static void main(String[] args) {
        User user = new User.Builder("Justin", "Riffhard")
                .state("CA")
                .country("USA")
                .build();

        Log.d(user.getState());
        Log.d(user.getCountry());
    }
}