How to overload a method by method with parameters list that contains parameters of the exact same type but parametrized with other types

问题

I have a methods:

public List<Integer> convertBy(Function<String, List<String>> flines, Function<List<String>, String> join, Function<String, List<Integer>> collectInts) {
    return collectInts.apply(join.apply(flines.apply((String) value)));
}//first method

public Integer convertBy(Function<List<String>, String> join, Function<String, List<Integer>> collectInts, Function<List<Integer>, Integer> sum) {
    return sum.apply(collectInts.apply(join.apply((List<String>) value)));
}//second method

Despite their parameteres are parametrized with different types I cannot overload the first method. I might use different interface, other than Function<T,R> but don't know which one would suffice as I went through list of them and couldn't find one https://docs.oracle.com/javase/8/docs/api/java/util/function/package-summary.html.

Parameters in those functions are:

flines - reads the file from given path (String) and returns list of lines in that file (List<String>)

join - concatenates element of given List<String> and returns a String

collectInts - parses the given String and returns List of integers found in that String.

sum - adds elements from List<Integers> and returns the sum

Questions:

Can I overload the first mehod by the second one?
What other existing functional interface I might use besides function? I think none, as the types of argument and result always differ.

回答1:

If you want to create a method which applies multiple functions and is not interested in the intermediate values, you can make it a generic method. The code in your question is strange as it assumes that value can be a String and a List<String> at the same time.

But comparing with your other question, there’s a different picture. While the varargs method there can’t work that way, you can easily provide overloaded methods for the actual use cases:

public class InputConverter<T> {

    private T value;

    public InputConverter(T value) {
        this.value = value;
    }
    public <R> R convertBy(Function<? super T, ? extends R> f) {
        return f.apply(value);
    }
    public <T1,R> R convertBy(
        Function<? super T, ? extends T1> f1, Function<? super T1, ? extends R> f2) {
        return f2.apply(f1.apply(value));
    }
    public <T1,T2,R> R convertBy(
        Function<? super T, ? extends T1> f1, Function<? super T1, ? extends T2> f2,
        Function<? super T2, ? extends R> f3) {
        return f3.apply(f2.apply(f1.apply(value)));
    }
    public <T1,T2,T3,R> R convertBy(
        Function<? super T, ? extends T1> f1, Function<? super T1, ? extends T2> f2,
        Function<? super T2, ? extends T3> f3, Function<? super T3, ? extends R> f4) {
        return f4.apply(f3.apply(f2.apply(f1.apply(value))));
    }
}

Assuming that you fixed your interface types and created functions as described in this answer, you can use it like

InputConverter<String> fileConv=new InputConverter<>("LamComFile.txt");
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);

来源：https://stackoverflow.com/questions/33256485/how-to-overload-a-method-by-method-with-parameters-list-that-contains-parameters

标签

java

generics

functional-interface