java - 构造函数应抛出 IllegalArgumentException(需要在 this() 之前检查)

Question

我希望我的构造函数抛出 IllegalArgumentException当使用错误的参数调用时，会显示一条自写的错误消息。

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

错误的参数意味着 TOP.get(top) (分别为左、右)为空，因为 Map<Integer, Integer>不包含这样的元素。问题是我无法首先测试 this()之前不允许使用代码。

Answer 1

添加一个帮助程序方法来检查输入:

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);
}