Java 8 Functional Interfaces

Java 8 has many functional interfaces as defined in the Javadoc. In this blog, I'm going to explain few important Java 8 functional interfaces.

• Consumer<T>
• Arguments: T
• Returns: Void
• Supplier<T>
• Arguments: None
• Returns: T
• Function<T, R>
• Arguments: T
• Returns: R
• Predicate<T>
• Arguments: T
• Returns: boolean
• UnaryOperator<T>
• Arguments: T
• Returns: T
• BinaryOperator<T>
• Arguments: (T, T)
• Returns: T

public class Java8 {
    public static void main(String[] args) {
        System.out.print("Consumer: ");
        Consumer<String> consumer = (s) -> {
            System.out.println(s);
        };
        consumer.accept("hello");

        System.out.print("Supplier: ");
        Supplier<String> supplier = () -> {
            return "foo";
        };
        System.out.println(supplier.get());
        
        System.out.print("Function: ");
        Function<Integer, String> function = (i) -> {
            return "func" + i;
        };
        System.out.println(function.apply(1));
        
        System.out.print("Predicate: ");
        Predicate<Integer> predicate = (i) -> {
            return i == 0;
        };
        System.out.println(predicate.test(0));
        
        System.out.print("UnaryOperator: ");
        UnaryOperator<Integer> unaryOperator = (i) -> {
            return i * 100;
        };
        System.out.println(unaryOperator.apply(2));
        
        System.out.print("BinaryOperator: ");
        BinaryOperator<Integer> binaryOperator = (i, j) -> {
            return i + j;
        };
        System.out.println(binaryOperator.apply(3, 5));
    }
}

Output:

Consumer: hello
Supplier: foo
Function: func1
Predicate: true
UnaryOperator: 200
BinaryOperator: 8