java - 为什么 c += 5 编译而不是 c = c + 5？

Question

这个问题在这里已经有了答案:





Why don't Java's +=, -=, *=, /= compound assignment operators require casting?

(11 个回答)


20 小时前关闭。




为什么当我们输入:

char c = 'A';
c += 5;

我们没有错误，但是当我们输入:

char c = 'A';
c = c + 5;

我们得到一个错误。我无法理解这是如何发生的，因为在我看来，这两个是相同的陈述。

Answer 1

+= , -=等运算符在 Java 中称为“复合赋值”。它们的语义包括 转换到目标类型 .
Oracle docs对此非常清楚:

A compound assignment expression of the form E1 op= E2 is equivalent to E1 = (T) ((E1) op (E2)), where T is the type of E1, except that E1 is evaluated only once.

For example, the following code is correct:

   short x = 3;
   x += 4.6;

and results in x having the value 7 because it is equivalent to:

   short x = 3;
   x = (short)(x + 4.6);

在您的示例中， c += 5;相当于 c = (char)(c + 5);