What are the purposes of functional interfaces BinaryOperator<T>, DoubleBinaryOperator, IntBinaryOperator, and LongBinaryOperator?

These functional interfaces are used to represent reduction or combination operations of two arguments of the same type, returning a result of the same type.

• BinaryOperator<T>: Accepts two arguments of type T and returns a result of type T.
• DoubleBinaryOperator: Accepts two arguments of type double and returns a result of type double.
• IntBinaryOperator: Accepts two arguments of type int and returns a result of type int.
• LongBinaryOperator: Accepts two arguments of type long and returns a result of type long.

They are often used in streams for aggregate operations such as summing or finding minimum/maximum.

Example of using IntBinaryOperator:

// Represents an operation of adding two ints
// Equivalent to (a, b) -> a + b
IntBinaryOperator sumOperator = Integer::sum;

int result = sumOperator.applyAsInt(5, 3); // result will be 8

Example of using BinaryOperator<T>:

// Represents an operation of finding the maximum of two Strings (lexicographically)
BinaryOperator<String> maxOperator = BinaryOperator.maxBy(String::compareTo);

String maxString = maxOperator.apply("apple", "banana"); // maxString will be "banana"