试图理解为什么两段相似的代码是不同的。 首先编译好。 二不

Question

// compare 2 Strings

BinaryOperator<String> maxLengthString = BinaryOperator.maxBy(
            Comparator.comparingInt(String::length));

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// compare 2 int

BinaryOperator<Integer> maxLengthString = BinaryOperator.maxBy(
            Comparator.comparingInt(Integer::compareTo));

Answer 1

String::length takes 1 String and returns 1 int.

Integer::compareTo takes 2 ints and returns 1 int.

Take a look at the methods' signature.

Answer 2

The compareTo method expects implicitly an argument to be passed. In this context the compiler can't retrieve the argument, so it throws a compile time error.