编写Java双功能和函数

Question

How can I compose a Bifunction with a function in the folowing example:

public static void main(String[] args) {
    BiFunction<String, Integer, String> zeroPadding = (string, zeros) -> String.format("%0" +zeros+ "d", Integer.valueOf(string));

    Function<String, String> removeNonDigitChars = (string) -> string.replaceAll("\\D", "");
}

First I want to remove non digits chars, and the removeNonDigitChars result pass to zeroPadding BiFunction with parameters.

I've tried:

zeroPadding.andThen(removeNonDigitChars).apply("789.65", 8);

and

removeNonDigitChars.compose(zeroPadding).apply("789.65", 8);

But none of two works.

Answer 1

Your two attempts are applying the functions in the wrong order. You want removeNonDigitChars applied to the string before giving the string to zeroPadding .

Unfortunately, you can't use andThen() or compose() to combined the two functions.

If you want a combined function, just combine them yourself:

BiFunction<String, Integer, String> combined = (string, zeros) ->
        zeroPadding.apply(removeNonDigitChars.apply(string), zeros);

Then use like this:

combined.apply("789.65", 8) // returns "00078965"