Sandwich example for https://jaxenter.de/pattern-java-8-lambda-43323

Sandwich.java

package patternexamples;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.function.Function;

public class Sandwich {

    private final String bread;

    private final String meat;
    
    private final String cheese;

    private final List<String> vegetables;

    private Sandwich(Builder builder) {
        this.bread = builder.bread;
        this.meat = builder.meat;
        this.cheese = builder.cheese;
        this.vegetables = Collections.unmodifiableList(builder.vegetables);
    }
    
    public String getBread() {
        return bread;
    }

    public String getCheese() {
        return cheese;
    }

    public String getMeat() {
        return meat;
    }

    public List<String> getVegetables() {
        return vegetables;
    }
    
    public Sandwich withAdditionalVeggies(final String vegetable) {
        return new Builder(this).addVeggie(vegetable).close().create();
    }
    
    public Sandwich withCheese(final String cheese) {
        return new Builder(this).withCheese(cheese).noVeggies().create();
    }
    
    public Sandwich removeCheese() {
        return new Builder(this).noCheese().close().create();
    }
    
    public static interface ChooseBreadStep {

        public ChooseMeatStep withMeat(final String meat);

        public AddVeggiesStep vegan();
    }

    public static interface ChooseMeatStep {

        public ChooseCheeseStep withCheese(final String cheese);

        public AddVeggiesStep noCheese();
    }

    public static interface ChooseCheeseStep {

        public AddVeggiesStep addVeggie(final String vegetable);

        public CloseStep noVeggies();
    }

    public static interface AddVeggiesStep {

        public AddVeggiesStep addVeggie(final String vegetable);

        public CloseStep close();
    }

    public static interface CloseStep {
        
        public Sandwich create();
    }

    private static class Builder implements ChooseBreadStep, ChooseMeatStep, ChooseCheeseStep, AddVeggiesStep, CloseStep {

        final String bread;

        String meat;

        String cheese;

        final List<String> vegetables = new ArrayList<>();

        Builder(String bread) {
            this.bread = bread;
        }
        
        Builder(Sandwich template) {
            this.bread = template.bread;
            this.meat = template.meat;
            this.cheese = template.cheese;            
            this.vegetables.addAll(template.vegetables);                        
        }

        @Override
        public ChooseMeatStep withMeat(String meat) {
            this.meat = meat;
            return this;
        }

        @Override
        public AddVeggiesStep vegan() {
            return this;
        }

        @Override
        public ChooseCheeseStep withCheese(String cheese) {
            this.cheese = cheese;
            return this;
        }

        @Override
        public AddVeggiesStep noCheese() {
            this.cheese = null;
            return this;
        }

        @Override
        public AddVeggiesStep addVeggie(String vegetable) {
            this.vegetables.add(vegetable);
            return this;
        }

        @Override
        public CloseStep noVeggies() {
            return this;
        }

        @Override
        public CloseStep close() {
            return this;
        }

        @Override
        public Sandwich create() {
            return new Sandwich(this);
        }
    }
        
    public static Sandwich make(String bread, Function<ChooseBreadStep, CloseStep> configuration) {
         return configuration.andThen(CloseStep::create).apply(new Builder(bread));
    }
            
    public static void main(final String...a) {        
        Sandwich.make("white", cfg -> cfg
                .withMeat("parma")
                .withCheese("cheedar")
                .addVeggie("salad")
                .close()
        );
        Sandwich.make("brown", cfg -> cfg
                .withMeat("salami")
                .noCheese()
                .close());
        Sandwich.make("spelt", cfg -> cfg
                .vegan()
                .addVeggie("salad")
                .addVeggie("gherkins")
                .addVeggie("tomatoes")
                .close()
        );
        Sandwich sandwich = Sandwich.make("white", cfg -> cfg
                .withMeat("parma")
                .withCheese("cheedar")
                .addVeggie("salad")
                .close()               
        );       
        sandwich = sandwich.removeCheese();        
        assert(sandwich.meat.equals("parma") && sandwich.cheese == null && sandwich.vegetables.size() == 1);
        sandwich = sandwich
                .withAdditionalVeggies("tomatoes")
                .withCheese("gouda");
        assert(sandwich.meat.equals("parma") && sandwich.cheese.equals("gouda") && sandwich.vegetables.size() == 2);
    }
}