Builder模式示例

如果类的构造器或者静态工厂中具有多个参数，设计这种类时， Builde模式就是一种不错的选择， 特别是当大多数参数都是可选或者类型相同的时候 。 与使用 重叠构造器模式相比，使用 Builder模式 的客户端代码将更 易于 阅读和编写，构建器也比 JavaBeans 更加安全

import java.util.EnumSet;
import java.util.Objects;
import java.util.Set;

public abstract class Pizza {
    public enum Topping {HAM, MUSHROOM, ONION, PEPPER, SAUSAGE}
    /**
     * 配料
     */
    final Set<Topping> toppings;

    abstract static class Builder<T extends Builder<T>> {
        EnumSet<Topping> toppings = EnumSet.noneOf(Topping.class);

        public T addTopping(Topping topping) {
            toppings.add(Objects.requireNonNull(topping));
            return self();
        }

        abstract Pizza build();

        protected abstract T self();
    }

    Pizza(Builder<?> builder) {
        this.toppings = builder.toppings.clone();
    }

    @Override
    public String toString() {
        return "Pizza{" +
                "toppings=" + toppings +
                '}';
    }
}

import java.util.Objects;

public class NyPizza extends Pizza {
    private final Size size;
    public enum Size {SMALL, MEDIUM, LARGE}
    private NyPizza(Builder builder) {
        super(builder);
        size = builder.size;
    }

    public static class Builder extends Pizza.Builder<Builder> {
        private final Size size;
        public Builder(Size size) {
            this.size = Objects.requireNonNull(size);
        }

        @Override
        NyPizza build() {
            return new NyPizza(this);
        }

        @Override
        protected Builder self() {
            return this;
        }
    }

    @Override
    public String toString() {
        return "NyPizza{" +
                "size=" + size +
                "} " + super.toString();
    }
}

public class CalZone extends Pizza {
    /**
     * 加酱
     */
    private final boolean sauceInside;
    private CalZone(Builder builder) {
        super(builder);
        sauceInside = builder.sauceInside;
    }

    public static class Builder extends Pizza.Builder<Builder> {
        // 默认不加酱
        private boolean sauceInside = false;

        public Builder sauceInside(){
            sauceInside = true;
            return this;
        }

        @Override
        CalZone build() {
            return new CalZone(this);
        }

        @Override
        protected Builder self() {
            return this;
        }
    }

    @Override
    public String toString() {
        return "CalZone{" +
                "sauceInside=" + sauceInside +
                "} " + super.toString();
    }
}

public class CalZone extends Pizza {
    /**
     * 加酱
     */
    private final boolean sauceInside;
    private CalZone(Builder builder) {
        super(builder);
        sauceInside = builder.sauceInside;
    }

    public static class Builder extends Pizza.Builder<Builder> {
        // 默认不加酱
        private boolean sauceInside = false;

        public Builder sauceInside(){
            sauceInside = true;
            return this;
        }

        @Override
        CalZone build() {
            return new CalZone(this);
        }

        @Override
        protected Builder self() {
            return this;
        }
    }

    @Override
    public String toString() {
        return "CalZone{" +
                "sauceInside=" + sauceInside +
                "} " + super.toString();
    }
}

import org.junit.Test;

import static builder.NyPizza.Size.SMALL;
import static builder.Pizza.Topping.*;

public class BuilderTest {
   @Test
   public void test(){
      NyPizza pizza = new NyPizza.Builder(SMALL)
              .addTopping(SAUSAGE)
              .addTopping(ONION)
              .build();
      System.out.println(pizza);

      CalZone calZone = new CalZone.Builder()
              .addTopping(HAM).sauceInside()
              .build();
      System.out.println(calZone);
   }
}