Using Java 8 Functional Interfaces to Replace if...else Statements

Function Functional Interface

Java 8 introduced the @FunctionalInterface annotation to mark interfaces that contain a single abstract method, enabling lambda expressions. The main functional interfaces are Supplier (no arguments, returns a value), Consumer (accepts one argument, returns void), Runnable (no arguments, no return), and Function (accepts an argument and returns a value).

Replacing if…else with Function

Instead of writing repetitive if…else blocks that throw exceptions or perform branching, you can define a functional interface such as ThrowExceptionFunction that encapsulates the logic and invoke it via a lambda.

/*** 抛异常接口 ***/
@FunctionalInterface
public interface ThrowExceptionFunction {
    void throwMessage(String message);
}
public static ThrowExceptionFunction isTrue(boolean b) {
    return (errorMessage) -> {
        if (b) {
            throw new RuntimeException(errorMessage);
        }
    };
}

Usage: VUtils.isTrue(condition).throwMessage("Error occurred"); – the method runs normally when the condition is false and throws an exception when true.

Branch handling

A BranchHandle interface can execute different Runnable actions based on a boolean value.

@FunctionalInterface
public interface BranchHandle {
    void trueOrFalseHandle(Runnable trueHandle, Runnable falseHandle);
}
public static BranchHandle isTrueOrFalse(boolean b) {
    return (trueHandle, falseHandle) -> {
        if (b) {
            trueHandle.run();
        } else {
            falseHandle.run();
        }
    };
}

Usage:

VUtils.isTrueOrFalse(flag).trueOrFalseHandle(() -> doTrue(), () -> doFalse());

Present‑or‑Else handling

The PresentOrElseHandler interface processes a value that may be null, executing a Consumer when the value is present and a Runnable otherwise.

@FunctionalInterface
public interface PresentOrElseHandler<T> {
    void presentOrElseHandle(Consumer<? super T> action, Runnable emptyAction);
}
public static PresentOrElseHandler<?> isBlankOrNoBlank(String str) {
    return (consumer, runnable) -> {
        if (str == null || str.length() == 0) {
            runnable.run();
        } else {
            consumer.accept(str);
        }
    };
}

Usage:

VUtils.isBlankOrNoBlank(text).presentOrElseHandle(s -> System.out.println(s), () -> System.out.println("empty"));

By leveraging these functional interfaces, Java code becomes more expressive and less cluttered with repetitive conditional statements.