Functional programming in Java can lead to more concise and expressive code, as it emphasizes the use of functions and immutable data structures. Additionally, it can help reduce the likelihood of errors and improve the overall maintainability of code.
Yes, it is possible to use object-oriented programming (OOP) and functional programming (FP) together.
functional programming encourages breaking down complex problems into smaller, more manageable functions that can be composed and combined to solve larger problems. This approach can help improve code modularity and make it easier to reason about and test individual components of a program.
A variable does never change in functional programming
Example
final int x = 4; // this does never change A pure function is a function that always returns the same output for a given input, without causing any side effects. It does not modify any external state or variables and does not rely on external state or variables. This makes pure functions easier to test, reason about, and parallelize.
Example 1
public int add(int x, int y) {
return x + y;
}Example 2
import java.util.Arrays;
public class PureFunctionExample {
public static void main(String[] args) {
int[] arr = {5, 3, 8, 2, 1};
int[] sortedArr = sort(arr);
System.out.println(Arrays.toString(sortedArr));
}
public static int[] sort(int[] arr) {
int[] newArr = arr.clone();
Arrays.sort(newArr);
return newArr;
}
}Example 3
public class PureFunctionExample {
public static void main(String[] args) {
String str = "Hello, World!";
String reversedStr = reverse(str);
System.out.println(reversedStr);
}
public static String reverse(String str) {
StringBuilder sb = new StringBuilder(str);
sb.reverse();
return sb.toString();
}
}In programming, first-class functions refer to the ability of a programming language to treat functions as first-class citizens, which means that functions can be treated like any other variable or data type. This means that functions can be assigned to variables, passed as arguments to other functions, and returned as values from functions.
Example 1
public class FirstClassFunctionExample {
protected static class SimpleMath {
public static Integer multiplyByThree(Integer x) {
return x * 3;
}
}
public static void main(String[] args) {
Function<Integer, Integer> simpleAdd = SimpleMath::multiplyByThree;
Integer x = 2;
// In order to utilize the function, you must make use of the apply method.
System.out.println(simpleAdd.apply(3));
}
}We can define a function without a class by using lambdas
Example 1
public class LambdaExample {
public static void main(String[] args) {
Function<Integer, Integer> someFunction = x -> x + 2;
Integer result = someFunction.apply(2);
System.out.println(result);
}
}Example 2
public class LambdaExample {
public static void main(String[] args) {
BiFunction<Integer, Integer, Integer> add = (a, b) -> a + b;
int sum = add.apply(5, 10);
System.out.println("The sum is: " + sum);
}
}We can define such a functional interface with multiple type parameters, as there is no built-in type for it.
Example 1
@FunctionalInterface
public interface TriFunction<T, U, V, R> {
R apply(T t, U u, V v);
}
public class FunctionExample {
public static void main(String[] args) {
TriFunction<Integer, Integer, Integer, Integer> add3 = (x, y, z) -> x + y + z;
Integer result = add3.apply(1, 2, 3);
System.out.println(result);
}
}Example 2
@FunctionalInterface
public interface VoidFunction<R>{
R apply();
}
public class FunctionExample {
public static void main(String[] args) {
VoidFunction<String> sayHello = () -> "Hello";
String result = sayHello.apply();
System.out.println(result);
}
}Example 1
package FunctionAsArgument.ExampleOne;
public class FunctionExample {
public static void main(String[] args) {
ArrayList<Integer> numbers = new ArrayList<>();
numbers.add(1);
numbers.add(2);
numbers.add(3);
numbers.add(4);
numbers.add(5);
numbers.add(100);
Function<Integer, Integer> square = n -> n * n;
ArrayList<Integer> squaredNumbers = map(numbers, square);
System.out.println(squaredNumbers);
}
public static ArrayList<Integer> map(ArrayList<Integer> numbers, Function<Integer, Integer> func) {
ArrayList<Integer> result = new ArrayList<>();
for (Integer number : numbers) {
result.add(func.apply(number));
}
return result;
}
}Example 2
public class FunctionExample {
public static void main(String[] args) {
String result = Processor.process(new Processor() {
@Override
public String apply(String input) {
return input.toLowerCase().replaceAll("\\s", "");
}
@Override
public String process(String input) {
return apply(apply(input));
}
}, "Christian Lehnert was here, Hiiii");
System.out.println(result);
}
private interface Processor {
String apply(String input);
String process(String input);
static String process(Processor p, String input) {
return p.process(input);
}
}
}Example 1
public class FunctionExample {
public static void main(String[] args) {
VoidFunction<VoidFunction<String>> greet = () -> () -> "Hello";
System.out.println(greet.apply().apply());
}
}Example 2
public class FunctionExample {
public static void main(String[] args) {
Function<Integer, Function<Integer, Integer>> xMultiply = times -> x -> x * times;
Function<Integer, Integer> timesFour = xMultiply.apply(4);
System.out.println(timesFour.apply(10));
Function<Integer, Integer> timesThree = xMultiply.apply(3);
System.out.println(timesThree.apply(10));
}
}Higher-order functions are functions that either take other functions as parameters or return functions as their results. They enable more concise and abstract code that can be reused in multiple contexts.
public class FunctionExample {
public static void main(String[] args) {
Function<Integer, Integer> applyTwice = x -> x * 2;
Consumer<Function<Integer, Integer>> printResult = f -> {
int result = f.apply(5);
System.out.println(result);
};
printResult.accept(applyTwice); // Output: 10
}
}