关于字节添加和分配的有趣观察 [英] Interesting observation on byte addition and assignment

问题描述

今天，在帮助某人时，我遇到了一个有趣的问题，我无法理解其原因.使用+ =时，我们不需要显式强制转换，但是当使用i + i时，我们需要显式强制转换.找不到确切原因.任何输入将不胜感激.

Today while helping someone I came across an interesting issue which I couldn't understand the reason. While using += we don't need to explicit casting, but when we use i+i, we need to explicitly cast. Couldn't find exact reason. Any input will be appreciated.

public class Test{
       byte c = 2;
       byte d = 5;

       public  void test(String args[])
       {
           c += 2;
           d = (byte) (d + 3);   
       }
    }

推荐答案

定义Java，以便+ =和其他复合赋值运算符自动将结果转换为要更新的变量的类型.结果，使用+ =时不需要强制类型转换，尽管仅使用普通运算符时也必须强制类型转换.您可以在Java语言规范中的

Java is defined such that += and the other compound assignment operators automatically cast the result to the type of the variable being updated. As a result, the cast isn't necessary when using +=, though it is necessary when just using the normal operators. You can see this in the Java Language Specification at http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.26.2

具体来说，表达式

a op= b

等同于

(a = (type of a)((a) op (b));

希望这会有所帮助！

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