java - 对角色进行一元运算后装箱

Question

  public static void main(String[] args) {
    Character x = ' ';
    while (x++ < 50) {
        int p = x;
    }
    System.out.println(x instanceof Character);
  }

因为是一元运算++。 x 在执行操作之前被拆箱为 char，然后扩展为 int。当我退出循环时，我得到“真”。我不明白如何将 int 装箱到 Character 后面； java 可以允许将 int 装箱为 Integer 或将 int 装箱并扩大为 Number、Object 等。

Answer 1

答案就在 Java 语言规范中 §15.14.2 Postfix Increment Operator ++

(我强调)

At run time, if evaluation of the operand expression completes abruptly, then the postfix increment expression completes abruptly for the same reason and no incrementation occurs. Otherwise, the value 1 is added to the value of the variable and the sum is stored back into the variable. Before the addition, binary numeric promotion (§5.6.2) is performed on the value 1 and the value of the variable. If necessary, the sum is narrowed by a narrowing primitive conversion (§5.1.3) and/or subjected to boxing conversion (§5.1.7) to the type of the variable before it is stored. The value of the postfix increment expression is the value of the variable before the new value is stored.