Java Academy · Lesson

Function and BiFunction

Transform values functionally.

What Function Represents

Function<T, R> is the core transformation interface in java.util.function. It takes one argument of type T and returns a result of type R.

Its single abstract method is R apply(T t).
It models a pure mapping from input to output.

import java.util.function.Function;

public class Main {
    public static void main(String[] args) {
        Function<String, Integer> length = s -> s.length();
        System.out.println(length.apply("hello"));
    }
}

Calling apply

You invoke a Function by calling apply. The lambda body is the transformation logic.

Input and output types can differ.
A method reference like String::toUpperCase can replace a lambda.

import java.util.function.Function;

public class Main {
    public static void main(String[] args) {
        Function<String, String> upper = String::toUpperCase;
        System.out.println(upper.apply("java"));
    }
}

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