java - 传递一些 lambda 作为方法的参数

Question

我想将一些 lambda 方法作为参数传递给该方法。不是一个 lambda，而是几个 lambda。如何做到这一点？

flines = arg -> arg.startsWith("WAW");

String fname = System.getProperty("user.home") + "/LamComFile.txt"; 

InputConverter<String> fileConv = new InputConverter<>(fname);

List<String> lines = fileConv.convertBy(flines);

String text = fileConv.convertBy(flines, join);

List<Integer> ints = fileConv.convertBy(flines, join, collectInts);

Integer sumints = fileConv.convertBy(flines, join, collectInts, sum);
    ...

Answer 1

我认为你必须编写返回类型取决于Function-argument的方法:

class InputConverter<T> {
   private final T value;

    public InputConverter(T value) {
        this.value = value;
    }

    public <R> R convertBy(Function<T, R> function){
        return function.apply(value);
    }
 }

然后您可以使用标准方法 compose 和 andThen 组合 Function 参数:

final String fname = "fname_value"

InputConverter<String> inputConverter = new InputConverter<>(fname);

Function<String, List<String>> valueToListFunction = Arrays::asList;
Function<List<String>, String> firstValueFunction = l -> l.get(0);

List<String> strings = inputConverter.convertBy(valueToListFunction);//[fname_value]
String firstValue = inputConverter.convertBy(
            valueToListFunction
                    .andThen(firstValueFunction)
);

您还可以使用其他标准FunctionalInterfaces，例如UnaryOperator:

UnaryOperator<String> firstChangeFunction = arg -> arg.concat(" + first");
UnaryOperator<String> secondChangeFunction = arg -> arg.concat(" + second");

String firstValue = inputConverter.convertBy(
            valueToListFunction
                    .andThen(firstValueFunction)
                    .andThen(secondChangeFunction)
                    .compose(firstChangeFunction)
); // sout: fname_value + first + second

或者自己写。