java中a + = 10和a = a + 10之间的区别？ [英] Difference between a += 10 and a = a + 10 in java?

问题描述

a + = 10 和 a = a + 10 两者是否相同，或者是否存在一些差异他们？我在用Java学习作业时遇到了这个问题。

Are a += 10 and a = a + 10 both the same, or is there some difference between them? I got this question while studying assignments in Java.

推荐答案

正如你现在提到的那样... ...这种情况：

As you've now mentioned casting... there is a difference in this case:

byte a = 5;
a += 10; // Valid
a = a + 10; // Invalid, as the expression "a + 10" is of type int

来自Java语言规范部15.26.2 ：

From the Java Language Specification section 15.26.2:

形式 E1 op = E2 的复合赋值表达式相当于
E1 =（T）（（E1）op（E2）），其中 T 是<$ c $的类型c> E1 ，但 E1 仅评估一次。

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.

有趣的是，他们在规范中给出的例子：

Interestingly, the example they give in the spec:

short x = 3;
x += 4.6;

在Java中有效，但在C＃中不是 ...基本上在C＃编译器执行+ =和 - =的特殊外壳，以确保表达式是目标类型或文件在目标类型范围内的文字。

is valid in Java, but not in C#... basically in C# the compiler performs special-casing of += and -= to ensure that the expression is either of the target type or is a literal within the target type's range.

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