英文:
how to return Consumer from Function interface
问题
以下是翻译的代码部分：
public static void main(String[] args) {
Function<Integer, Integer> factorial = n -> IntStream.rangeClosed(2, n)
.reduce(1, (x, y) -> x * y);
Function<Integer, Consumer<Integer>> f3 = n -> {
return x -> System.out.println(factorial.apply(x * factorial.apply(n)));
};
f3.apply(5).accept(2); // 输出 0
}
请问您还有其他需要帮助的地方吗？
英文:
I have learning functional interfaces. I have written below code to return a Consumer from Function interface but it's not working. It's returning output 0. I don't understand why it returning0.
Code:
public static void main(String[] args) {
Function<Integer, Integer> factorial = n -> IntStream.rangeClosed(2, n)
.reduce(1, (x, y) -> x * y);
Function<Integer, Consumer<Integer>> f3 = n -> {
return x -> System.out.println(factorial.apply(x * factorial.apply(n)));
};
f3.apply(5).accept(2); // output 0
}
Can someone explain why this is(f3.apply(5).accept(2)) returning 0. Is there any other way to implement this.
答案1
得分: 3
public static void main(String[] args) throws IOException {
Function<Integer, BigInteger> factorial = n -> {
BigInteger res = BigInteger.ONE;
for (int i = 2; i <= n; i++)
res = res.multiply(BigInteger.valueOf(i));
return res;
};
Function<Integer, Consumer<Integer>> f3 = n -> {
return (Consumer<Integer>)x -> {
BigInteger fact = factorial.apply(n);
fact = fact.multiply(BigInteger.valueOf(x));
System.out.println(factorial.apply(fact.intValue()));
};
};
f3.apply(5).accept(2);
}
英文:
public static void main(String[] args) throws IOException {
Function<Integer, BigInteger> factorial = n -> {
BigInteger res = BigInteger.ONE;
for (int i = 2; i <= n; i++)
res = res.multiply(BigInteger.valueOf(i));
return res;
};
Function<Integer, Consumer<Integer>> f3 = n -> { // n = 5
return (Consumer<Integer>)x -> { // x = 2
BigInteger fact = factorial.apply(n); // 120 - correct
fact = fact.multiply(BigInteger.valueOf(x)); // 240
System.out.println(factorial.apply(fact.intValue())); // too big for int and long
};
};
f3.apply(5).accept(2); // 4067885363647058120493575921486885310172051259182827146069755969081486918925585104009100729728348522923820890245870098659147156051905732563147381599098459244752463027688115705371704628286326621238456543307267608612545168337779669138759451760395968217423617954330737034164596496963986817722252221059768080852489940995605579171999666916004042965293896799800598079985264195119506681577622056215044851618236292136960000000000000000000000000000000000000000000000000000000000
}
答案2
得分: 1
得到Consumer变量后，您需要将代码拆分为两部分
Consumer<Integer> c = f3.apply(2);
// x -> System.out.println(factorial.apply(x * factorial.apply(5)))
c.accept(2);
从这里您可以看出，有些东西无法找到，因为您的consumer将执行(x * 5!)!，这是(120x)!，所以对于2 -> 240!约为10^468，而整数只能保存最多2^32。
我建议您去掉一个层次的factorial以获得更容易理解的结果
Function<Integer, Consumer<Integer>> f3 = n -> x -> {
System.out.println(x * factorial.apply(n));
};
Consumer<Integer> c = f3.apply(5);
c.accept(1); // 120
c.accept(2); // 240
c.accept(3); // 360
c.accept(4); // 480
英文:
To get the Consumer in a variable, you need to split your code in 2 parts
Consumer<Integer> c = f3.apply(2);
//x -> System.out.println(factorial.apply(x * factorial.apply(5)))
c.accept(2);
From here you see that something is not gonna be find, as your consumer will do (x * 5!)! which is (120x)! so with 2 -> 240!about 10^468, where an integer can hold only up to 2^32
I'd suggest you remove a level of factorial to get easier results to understand
Function<Integer, Consumer<Integer>> f3 = n -> x -> {
System.out.println(x * factorial.apply(n));
};
Consumer<Integer> c = f3.apply(5);
c.accept(1); // 120
c.accept(2); // 240
c.accept(3); // 360
c.accept(4); // 480
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