Java 8链lambda

Question

我正在玩java lambdas,这是我目前的代码:

public class TypeChecker<T> {
    private T value;
    private Class clazz;
    private UnaryOperator<T> callback;

    private TypeChecker(T value) {
        this.value = value;
    }

    public static TypeChecker<String> when(String v) {
        return new TypeChecker<>(v);
    }

    public static TypeChecker<Integer> when(int v) {
        return new TypeChecker<>(v);
    }

    public TypeChecker<T> is(Class clazz) {
        this.clazz = clazz;
        return this;
    }

    public TypeChecker<T> then(UnaryOperator<T> callback) {
        this.callback = callback;
        return this;
    }

    public void execute() {
        if (clazz.isInstance(value)) {
            callback.apply(value);
        }
    }
}

TypeChecker.when("123").is(String.class).then(s -> {
    return s;
}).execute();

TypeChecker.when(123).is(Integer.class).then(n -> {
    return n;
}).execute();

在这里,我只是检查instanceOf变量及其工作正常.我想要实现的是这样的:

TypeChecker.when(123)
.is(String.class).then(s -> {
    return s;
})
.is(Integer.class).then(n -> {
    return n;
})
.is(Double.class).then(d -> {
    return d;
}).execute();

现在我如何链接它？我很困惑,我应该在哪里保存Clazz&Callbacks？我应该将它存储在地图中并执行方法只需迭代并检查吗？

Answer 1

您的问题让我想起了lambda表达式构建器模式.我将引入一个新的界面做的is().then()操作,并将其添加到Map在TypeChecker这样的:

class Matcher<T> {

  private final Map<Class<?>, UnaryOperator> mapping = new HashMap<>();
  private final T value;

  private Matcher(T value) {
    this.value = value;
  }

  public static <T> Matcher<T> when(T v) {
    return new Matcher<>(v);
  }

  public <S> Condition<S> is(Class<S> clazz) {
    return callback -> {
      mapping.put(clazz, callback);
      return this;
    };
  }

  public void execute() {
    mapping.forEach((key, val) -> {
      if (key.isInstance(value)) {
        val.apply(value);
      }
    });
  }

  interface Condition<S> {
    Matcher<?> then(UnaryOperator<? super S> callback);
  }
}

轻松测试,并应产生您想要的结果:

Matcher.when(123).is(String.class).then(s -> {
  System.out.println("STRING");
  return s;
})
        .is(Integer.class).then(i -> {
  System.out.println("INTEGER");
  return i;
}).execute();