Constructor shall throw IllegalArgumentException (need check before this())

principal-ideal-domain :

I want my constructor to throw an IllegalArgumentException with a self written error message when it is called with wrong arguments.

public Card(int top, int left, int right) {
    this(TOP.get(top) + 3 * LEFT.get(left) + 9 * RIGHT.get(right));
}

Wrong arguments mean that TOP.get(top) (resp. LEFT, RIGHT) is null since the Map<Integer, Integer> doesn't contain such an element. The problem is that I can't test for that first since this() doesn't allow code before.

Stefan :

Add a helper method that checks the input for you:

public Card(int top, int left, int right) {
    this(helper(top, left, right));
}

private static int helper(int top, int left, int right) {
    if (TOP.get(top) == null || LEFT.get(left) == null || RIGHT.get(right) == null)) {  
        throw new IllegalArgumentException();
    }
    return TOP.get(top) + 3 * LEFT.get(left) + 9 * RIGHT.get(right);
}

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