Java – what is the best way to test this? Binary number with 4 positions

Consider the four input fields a, B, C and D on the web surface. Users can fill in any of these There are 16 combinations of how to fill these fields Allowed are:

A B C D
-------
1 0 0 0
1 1 0 0
1 1 1 0
1 1 1 1

Where 1 means not null and 0 means null

I'm using JSF's MVC mode I don't want the logic in the view, but in the controller What is the best way to check this in Java?

So far, I have implemented two solutions

Solution 1:

@Override
public boolean isInputInvalid(Integer a,Integer b,Integer c,Integer d) {
    if (isNotSet(a) && isNotSet(b) && isNotSet(c) && isNotSet(d) {
        return true;
    }
    return (firstParameterDoesNotExistAndSecondDoesExist(a,b)) || (firstParameterDoesNotExistAndSecondDoesExist(b,c)) || (firstParameterDoesNotExistAndSecondDoesExist(c,d));
}

private boolean firstParameterDoesNotExistAndSecondDoesExist(Integer firstParameter,Integer secondParameter) {
    return isNotSet(firstParameter) && !isNotSet(secondParameter);
}

private boolean isNotSet(Integer parameter) {
    return parameter == null;
}

Solution 2:

public boolean isInputValid(Integer a,Integer d) {
    if (exists(a) && !exists(b) && !exists(c) && !exists(d) || //
            exists(a) && exists(b) && !exists(c) && !exists(d) || //
            exists(a) && exists(b) && exists(c) && !exists(d) || //
            exists(a) && exists(b) && exists(c) && exists(d)) {
        return true;
    }
    return false;
}

private boolean exists(Integer level) {
    return level != null;
}

be careful:

The first method checks whether the input is invalid, and the second method checks whether the input is valid (pay attention to the name of the method)

I wrote 16 unit test cases, and both versions run green

Do you have any tips / Tricks / tips on how to make your code more readable?

Solution

If you only care about readability:

public static List<String> validOptions = Arrays.asList("1000","1100","1110","1111");

public boolean isValid(Integer a,Integer d)
{
    StringBuilder sb = new StringBuilder();
    sb.append(a==null ? 0 : 1); 
    sb.append(b==null ? 0 : 1),sb.append(c==null ? 0 : 1); 
    sb.append(d==null ? 0 : 1);
    return validOptions.contains(sb.toString());
}

Note that this is not the fastest or cleanest solution (wasting some CPU and memory)