java - Java 中的异或字节

Question

Java 不支持对字节的按位操作。我想像这样异或两个字节:

xoredByte = byte1 ^ byte2;

在 java 中，这必须按以下方式完成:

xoredByte = (byte) (byte1 ^ byte2);

编译为:

xoredByte = (byte) ((int)byte1 ^ (int)byte2);

这是否适用于所有情况？我的意思是，这些是等价的陈述吗？

如果不是，执行此操作的代码是什么？

Answer 1

是的，这两种说法是等价的。通常使用二元运算符(包括 ^)时，Java 对两个操作数应用“二进制数字提升”以确保它们至少都是 int 值。 Section 5.6.2 of the JLS包括这个:

When an operator applies binary numeric promotion to a pair of operands, each of which must denote a value that is convertible to a numeric type, the following rules apply, in order:

• If any operand is of a reference type, it is subjected to unboxing conversion (§5.1.8).

• Widening primitive conversion (§5.1.2) is applied to convert either or both operands as specified by the following rules:

• If either operand is of type double, the other is converted to double.

• Otherwise, if either operand is of type float, the other is converted to float.

• Otherwise, if either operand is of type long, the other is converted to long.

• Otherwise, both operands are converted to type int.

(强调我的)

和

Binary numeric promotion is performed on the operands of certain operators:

• The multiplicative operators *, /, and % (§15.17)

• The addition and subtraction operators for numeric types + and - (§15.18.2)

• The numerical comparison operators <, <=, >, and >= (§15.20.1)

• The numerical equality operators == and != (§15.21.1)

• The integer bitwise operators &, ^, and | (§15.22.1)

• In certain cases, the conditional operator ? : (§15.25)

(强调我的)

无论是否应用 (int) 转换，byte1 和 byte2 都将被提升为 int 手术前。这也是为什么需要转换回 (byte) 的原因。