Replace Cluttered if…else with Java 8 Functional Interfaces

In Java development, excessive if...else... statements can make code hard to read. Using Java 8 functional interfaces provides a cleaner alternative.

Function Functional Interface

Mark an interface with @FunctionalInterface to indicate it has a single abstract method. Common built‑in functional interfaces include:

Supplier : no arguments, returns a value.

Consumer : accepts one argument, returns void.

Runnable : no arguments, no return value.

Function : accepts one argument and returns a value.

Tip: Handling Exception‑Throwing if

1. Define a functional interface that throws an exception.

/** * 抛异常接口 */
@FunctionalInterface
public interface ThrowExceptionFunction {
    void throwMessage(String message);
}

2. Create a utility method that returns an instance based on a boolean flag.

public static ThrowExceptionFunction isTrue(boolean b) {
    return (errorMessage) -> {
        if (b) {
            throw new RuntimeException(errorMessage);
        }
    };
}

3. Use it:

ThrowExceptionFunction f = VUtils.isTrue(flag); f.throwMessage("error");

Handling if‑branch with Functional Interfaces

1. Define a BranchHandle interface.

@FunctionalInterface
public interface BranchHandle {
    void trueOrFalseHandle(Runnable trueHandle, Runnable falseHandle);
}

2. Utility method returning BranchHandle based on a condition.

public static BranchHandle isTrueOrFalse(boolean b) {
    return (trueHandle, falseHandle) -> {
        if (b) {
            trueHandle.run();
        } else {
            falseHandle.run();
        }
    };
}

PresentOrElse Handling for Nullable Values

1. Define a PresentOrElseHandler interface.

public interface PresentOrElseHandler<T extends Object> {
    void presentOrElseHandle(Consumer<? super T> action, Runnable emptyAction);
}

2. Utility method that returns the handler based on string emptiness.

public static PresentOrElseHandler<?> isBlankOrNoBlank(String str) {
    return (consumer, runnable) -> {
        if (str == null || str.length() == 0) {
            runnable.run();
        } else {
            consumer.accept(str);
        }
    };
}