java - 用于 Bigdecimal 空验证的三元运算符

Question

为什么我在这段代码中遇到空指针异常？

    BigDecimal test = null;
    String data = "";
    try {
    System.out.println(test==null?"":test.toString());
    data = test==null?"":test.toString();
    System.out.println(data);
    data = data +  " " + test==null?"":test.toString(); // catching null pointer in this line
    } catch (Exception e) {
        // TODO: handle exception
        e.printStackTrace();
    }

Answer 1

它将表达式计算为:

data = (data +  " " + test==null)?"":test.toString();

因此，由于 data + ""+ test 不是 null，它会尝试调用 test.toString()，即使 >test 为 null。

改变

data = data +  " " + test==null?"":test.toString();

至

data = data +  " " + (test==null?"":test.toString());