Check for null object and null value contained in object in Java 8 way

Question

how to rewrite this function to be more Java 8 with Optionals? Or should I just leave it as it is?

public void setMemory(ArrayList<Integer> memory) {
    if (memory == null)
        throw new IllegalArgumentException("ERROR: memory object can't be null.");
    if (memory.contains(null))
        throw new IllegalArgumentException("ERROR: memory object can't contain null value.");

    this.memory = memory;
}

Answer 1

For the first case I would use: Objects.requireNonNull().

I don't think Optional is a way to go here as null is an illegal value.

Answer 2

You've got a pattern condition -> throw an exception which can be moved to a method:

private void checkOrElseThrow(boolean condition, Supplier<? extends RuntimeException> exceptionSupplier) {
    if (condition) {
        throw exceptionSupplier.get();
    }
}

public void setMemory(List<Integer> memory) {

    checkOrElseThrow(memory == null, () -> new IllegalArgumentException("message #1"));
    checkOrElseThrow(memory.contains(null), () -> new IllegalArgumentException("message #2"));

    this.memory = memory;
}

If the type of the exception is not going to be changed, it's reasonable to pass only the message of the exception (thank @tobias_k for pointing it out):

private void checkOrElseThrow(boolean condition, String exceptionMessage) {
    if (condition) {
        throw new IllegalArgumentException(exceptionMessage);
    }
}

public void setMemory(List<Integer> memory) {

    checkOrElseThrow(memory == null, "message #1");
    checkOrElseThrow(memory.contains(null), "message #2");

    this.memory = memory;
}