Java Lambda

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Lambda 示例

源码来源: Github java-design-patterns/factory-kit

基础类

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public interface Weapon {
}
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public enum WeaponType {
  SWORD, AXE, BOW, SPEAR
}
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public class Sword implements Weapon {
  @Override
  public String toString() {
    return "Sword";
  }
}

public class Axe implements Weapon {
  @Override
  public String toString() {
    return "Axe";
  }
}

// Bow Spear 略 
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import java.util.function.Supplier;

public interface Builder {
  void add(WeaponType name, Supplier<Weapon> supplier);
}
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import java.util.HashMap;
import java.util.Map;
import java.util.function.Consumer;
import java.util.function.Supplier;

public interface WeaponFactory {

  Weapon create(WeaponType name);

  static WeaponFactory factory(Consumer<Builder> consumer) {
    Map<WeaponType, Supplier<Weapon>> map = new HashMap<>();
    consumer.accept(map::put);
    return name -> map.get(name).get();
  }
}

非 Lambda 方式实现 WeaponFactory

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static WeaponFactory factory2(Consumer<Builder> consumer) {
    Map<WeaponType, Supplier<Weapon>> map = new HashMap<>();

    // accept 实现方式 1
    // consumer.accept(((name, supplier) -> map.put(name, supplier)));

    // accept 实现方式 2
    consumer.accept(new Builder() {
        @Override
        public void add(WeaponType name, Supplier<Weapon> supplier) {
            map.put(name, supplier);
        }
    });
    // create 非 lambda 实现方式 
    return new WeaponFactory() {
        @Override
        public Weapon create(WeaponType name) {
            return map.get(name).get();
        }
    };
}

Lambda 方式初始化 WeaponFactory

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private static WeaponFactory getWeaponFactory_lam() {
    return WeaponFactory.factory(builder -> {
        builder.add(WeaponType.SWORD, Sword::new);
        builder.add(WeaponType.AXE, Axe::new);
        builder.add(WeaponType.SPEAR, Spear::new);
        builder.add(WeaponType.BOW, Bow::new);
    });
}

非 Lambda 方式初始化 WeaponFactory

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private static WeaponFactory getWeaponFactory() {
    return WeaponFactory.factory(new Consumer<Builder>() {
        @Override
        public void accept(Builder builder) {
            builder.add(WeaponType.SWORD, new Supplier<Weapon>() {
                @Override
                public Weapon get() {
                    return new Sword();
                }
            });
            builder.add(WeaponType.AXE, () -> new Axe());
            builder.add(WeaponType.SPEAR, Spear::new);
        }
    });
}

相关资料