我正在尝试为一种非常简单的加密类型编写一个解码器。通过扫描仪输入 0-255 的数字，将位反转，然后转换为字符并打印。
例如，数字 178 应转换为字母“M”。
178 是 10110010。
反转所有位应得到 01001101，即 77 或“M”作为字符。
我遇到的主要问题是，据我所知，Java 不支持无符号字节。我可以将值读取为 int 或短整型，但由于额外的位，这些值将在转换过程中关闭。理想情况下，我可以只使用按位补码运算符，但我认为如果我使用带符号的数字执行此操作，我最终会得到负值。关于我应该如何处理这个问题有什么想法吗？
我会简单地使用个补码并通过使用二进制 and 去掉其他位。
public class Conv {
public static void main(String[] args) {
int val = 178;
val = ~val & 0xff;
System.out.println((char) val);
}
}
~n & 0xff
~& 0xff我首先以不同的方式阅读你的问题，反转顺序而不是位的值，这就是答案。
Integer.reverse()Integer.reverse(n << 24) & 0xff
Java 中的位运算是为
intintbyteScanner.nextIntScanner.nextByte将数字存储在整数中后，要翻转最低有效的 8 位，您可以与 0xff 进行异或。对于 0 到 255 之间的所有输入，这应该按您的预期工作：
x ^= 0xff;
示例：
String input = "178 0 255";
Scanner s = new Scanner(input);
while (s.hasNextInt()) {
int x = s.nextInt();
if (x < 0 || x > 255) {
System.err.println("Not in range 0-255: " + x);
} else {
x ^= 0xff;
System.out.println(x);
}
}
结果：
77
255
0
如果 Java 支持这一点，您可以将其读入更大的类型，按位补足，然后位屏蔽掉不需要的位。
int x = [your byte];
x = ~x & 0xFF;
最简单的方法是三个阶段：
int i = scanner.nextByte();i = ~i;i = i & 0xFF;然后将结果用作字符（在java中实际上是16位，但我们只会使用其中的8位）：
char c=(char)a;
System.out.println(c);
大家一起：
int i = scanner.nextByte(); // change this to nextInt() depending on file format
i = ~i;
i = i & 0xFF;
char c=(char)a;
System.out.println(c);
或者，您可以在不使用任何狡猾的签名算术的情况下完成此操作，而是使用字符串处理：-
public class ReverseBits {
public static void main(String[] args) {
byte[] reversedBits = {
(byte) 0b00000000,
(byte) 0b10000000,
(byte) 0b01000000,
(byte) 0b11000000,
(byte) 0b00100000,
(byte) 0b10100000,
(byte) 0b01100000,
(byte) 0b11100000,
(byte) 0b00010000,
(byte) 0b10010000,
(byte) 0b01010000,
(byte) 0b11010000,
(byte) 0b00110000,
(byte) 0b10110000,
(byte) 0b01110000,
(byte) 0b11110000,
(byte) 0b00001000,
(byte) 0b10001000,
(byte) 0b01001000,
(byte) 0b11001000,
(byte) 0b00101000,
(byte) 0b10101000,
(byte) 0b01101000,
(byte) 0b11101000,
(byte) 0b00011000,
(byte) 0b10011000,
(byte) 0b01011000,
(byte) 0b11011000,
(byte) 0b00111000,
(byte) 0b10111000,
(byte) 0b01111000,
(byte) 0b11111000,
(byte) 0b00000100,
(byte) 0b10000100,
(byte) 0b01000100,
(byte) 0b11000100,
(byte) 0b00100100,
(byte) 0b10100100,
(byte) 0b01100100,
(byte) 0b11100100,
(byte) 0b00010100,
(byte) 0b10010100,
(byte) 0b01010100,
(byte) 0b11010100,
(byte) 0b00110100,
(byte) 0b10110100,
(byte) 0b01110100,
(byte) 0b11110100,
(byte) 0b00001100,
(byte) 0b10001100,
(byte) 0b01001100,
(byte) 0b11001100,
(byte) 0b00101100,
(byte) 0b10101100,
(byte) 0b01101100,
(byte) 0b11101100,
(byte) 0b00011100,
(byte) 0b10011100,
(byte) 0b01011100,
(byte) 0b11011100,
(byte) 0b00111100,
(byte) 0b10111100,
(byte) 0b01111100,
(byte) 0b11111100,
(byte) 0b00000010,
(byte) 0b10000010,
(byte) 0b01000010,
(byte) 0b11000010,
(byte) 0b00100010,
(byte) 0b10100010,
(byte) 0b01100010,
(byte) 0b11100010,
(byte) 0b00010010,
(byte) 0b10010010,
(byte) 0b01010010,
(byte) 0b11010010,
(byte) 0b00110010,
(byte) 0b10110010,
(byte) 0b01110010,
(byte) 0b11110010,
(byte) 0b00001010,
(byte) 0b10001010,
(byte) 0b01001010,
(byte) 0b11001010,
(byte) 0b00101010,
(byte) 0b10101010,
(byte) 0b01101010,
(byte) 0b11101010,
(byte) 0b00011010,
(byte) 0b10011010,
(byte) 0b01011010,
(byte) 0b11011010,
(byte) 0b00111010,
(byte) 0b10111010,
(byte) 0b01111010,
(byte) 0b11111010,
(byte) 0b00000110,
(byte) 0b10000110,
(byte) 0b01000110,
(byte) 0b11000110,
(byte) 0b00100110,
(byte) 0b10100110,
(byte) 0b01100110,
(byte) 0b11100110,
(byte) 0b00010110,
(byte) 0b10010110,
(byte) 0b01010110,
(byte) 0b11010110,
(byte) 0b00110110,
(byte) 0b10110110,
(byte) 0b01110110,
(byte) 0b11110110,
(byte) 0b00001110,
(byte) 0b10001110,
(byte) 0b01001110,
(byte) 0b11001110,
(byte) 0b00101110,
(byte) 0b10101110,
(byte) 0b01101110,
(byte) 0b11101110,
(byte) 0b00011110,
(byte) 0b10011110,
(byte) 0b01011110,
(byte) 0b11011110,
(byte) 0b00111110,
(byte) 0b10111110,
(byte) 0b01111110,
(byte) 0b11111110,
(byte) 0b00000001,
(byte) 0b10000001,
(byte) 0b01000001,
(byte) 0b11000001,
(byte) 0b00100001,
(byte) 0b10100001,
(byte) 0b01100001,
(byte) 0b11100001,
(byte) 0b00010001,
(byte) 0b10010001,
(byte) 0b01010001,
(byte) 0b11010001,
(byte) 0b00110001,
(byte) 0b10110001,
(byte) 0b01110001,
(byte) 0b11110001,
(byte) 0b00001001,
(byte) 0b10001001,
(byte) 0b01001001,
(byte) 0b11001001,
(byte) 0b00101001,
(byte) 0b10101001,
(byte) 0b01101001,
(byte) 0b11101001,
(byte) 0b00011001,
(byte) 0b10011001,
(byte) 0b01011001,
(byte) 0b11011001,
(byte) 0b00111001,
(byte) 0b10111001,
(byte) 0b01111001,
(byte) 0b11111001,
(byte) 0b00000101,
(byte) 0b10000101,
(byte) 0b01000101,
(byte) 0b11000101,
(byte) 0b00100101,
(byte) 0b10100101,
(byte) 0b01100101,
(byte) 0b11100101,
(byte) 0b00010101,
(byte) 0b10010101,
(byte) 0b01010101,
(byte) 0b11010101,
(byte) 0b00110101,
(byte) 0b10110101,
(byte) 0b01110101,
(byte) 0b11110101,
(byte) 0b00001101,
(byte) 0b10001101,
(byte) 0b01001101,
(byte) 0b11001101,
(byte) 0b00101101,
(byte) 0b10101101,
(byte) 0b01101101,
(byte) 0b11101101,
(byte) 0b00011101,
(byte) 0b10011101,
(byte) 0b01011101,
(byte) 0b11011101,
(byte) 0b00111101,
(byte) 0b10111101,
(byte) 0b01111101,
(byte) 0b11111101,
(byte) 0b00000011,
(byte) 0b10000011,
(byte) 0b01000011,
(byte) 0b11000011,
(byte) 0b00100011,
(byte) 0b10100011,
(byte) 0b01100011,
(byte) 0b11100011,
(byte) 0b00010011,
(byte) 0b10010011,
(byte) 0b01010011,
(byte) 0b11010011,
(byte) 0b00110011,
(byte) 0b10110011,
(byte) 0b01110011,
(byte) 0b11110011,
(byte) 0b00001011,
(byte) 0b10001011,
(byte) 0b01001011,
(byte) 0b11001011,
(byte) 0b00101011,
(byte) 0b10101011,
(byte) 0b01101011,
(byte) 0b11101011,
(byte) 0b00011011,
(byte) 0b10011011,
(byte) 0b01011011,
(byte) 0b11011011,
(byte) 0b00111011,
(byte) 0b10111011,
(byte) 0b01111011,
(byte) 0b11111011,
(byte) 0b00000111,
(byte) 0b10000111,
(byte) 0b01000111,
(byte) 0b11000111,
(byte) 0b00100111,
(byte) 0b10100111,
(byte) 0b01100111,
(byte) 0b11100111,
(byte) 0b00010111,
(byte) 0b10010111,
(byte) 0b01010111,
(byte) 0b11010111,
(byte) 0b00110111,
(byte) 0b10110111,
(byte) 0b01110111,
(byte) 0b11110111,
(byte) 0b00001111,
(byte) 0b10001111,
(byte) 0b01001111,
(byte) 0b11001111,
(byte) 0b00101111,
(byte) 0b10101111,
(byte) 0b01101111,
(byte) 0b11101111,
(byte) 0b00011111,
(byte) 0b10011111,
(byte) 0b01011111,
(byte) 0b11011111,
(byte) 0b00111111,
(byte) 0b10111111,
(byte) 0b01111111,
(byte) 0b11111111
};
for (var i = 0; i < 256; i++) {
var b = (byte) i;
var s = String.format("%8s", Integer.toBinaryString(b & 0xFF)).replace(' ', '0');
var reversedString = new StringBuilder();
reversedString.append(s);
reversedString = reversedString.reverse();
var sR = reversedString.toString();
System.out.println(i + ", " + s + ", " + sR + ", " + (byte) i + ", " + reversedBits[i]);
}
产生：-
0, 00000000, 00000000, 0, 0
1, 00000001, 10000000, 1, -128
2, 00000010, 01000000, 2, 64
3, 00000011, 11000000, 3, -64
4, 00000100, 00100000, 4, 32
5, 00000101, 10100000, 5, -96
6, 00000110, 01100000, 6, 96
7, 00000111, 11100000, 7, -32
8, 00001000, 00010000, 8, 16
9, 00001001, 10010000, 9, -112
10, 00001010, 01010000, 10, 80
11, 00001011, 11010000, 11, -48
12, 00001100, 00110000, 12, 48
13, 00001101, 10110000, 13, -80
14, 00001110, 01110000, 14, 112
15, 00001111, 11110000, 15, -16
16, 00010000, 00001000, 16, 8
17, 00010001, 10001000, 17, -120
18, 00010010, 01001000, 18, 72
19, 00010011, 11001000, 19, -56
20, 00010100, 00101000, 20, 40
21, 00010101, 10101000, 21, -88
22, 00010110, 01101000, 22, 104
23, 00010111, 11101000, 23, -24
24, 00011000, 00011000, 24, 24
25, 00011001, 10011000, 25, -104
26, 00011010, 01011000, 26, 88
27, 00011011, 11011000, 27, -40
28, 00011100, 00111000, 28, 56
29, 00011101, 10111000, 29, -72
30, 00011110, 01111000, 30, 120
31, 00011111, 11111000, 31, -8
32, 00100000, 00000100, 32, 4
33, 00100001, 10000100, 33, -124
34, 00100010, 01000100, 34, 68
35, 00100011, 11000100, 35, -60
36, 00100100, 00100100, 36, 36
37, 00100101, 10100100, 37, -92
38, 00100110, 01100100, 38, 100
39, 00100111, 11100100, 39, -28
40, 00101000, 00010100, 40, 20
41, 00101001, 10010100, 41, -108
42, 00101010, 01010100, 42, 84
43, 00101011, 11010100, 43, -44
44, 00101100, 00110100, 44, 52
45, 00101101, 10110100, 45, -76
46, 00101110, 01110100, 46, 116
47, 00101111, 11110100, 47, -12
48, 00110000, 00001100, 48, 12
49, 00110001, 10001100, 49, -116
50, 00110010, 01001100, 50, 76
51, 00110011, 11001100, 51, -52
52, 00110100, 00101100, 52, 44
53, 00110101, 10101100, 53, -84
54, 00110110, 01101100, 54, 108
55, 00110111, 11101100, 55, -20
56, 00111000, 00011100, 56, 28
57, 00111001, 10011100, 57, -100
58, 00111010, 01011100, 58, 92
59, 00111011, 11011100, 59, -36
60, 00111100, 00111100, 60, 60
61, 00111101, 10111100, 61, -68
62, 00111110, 01111100, 62, 124
63, 00111111, 11111100, 63, -4
64, 01000000, 00000010, 64, 2
65, 01000001, 10000010, 65, -126
66, 01000010, 01000010, 66, 66
67, 01000011, 11000010, 67, -62
68, 01000100, 00100010, 68, 34
69, 01000101, 10100010, 69, -94
70, 01000110, 01100010, 70, 98
71, 01000111, 11100010, 71, -30
72, 01001000, 00010010, 72, 18
73, 01001001, 10010010, 73, -110
74, 01001010, 01010010, 74, 82
75, 01001011, 11010010, 75, -46
76, 01001100, 00110010, 76, 50
77, 01001101, 10110010, 77, -78
78, 01001110, 01110010, 78, 114
79, 01001111, 11110010, 79, -14
80, 01010000, 00001010, 80, 10
81, 01010001, 10001010, 81, -118
82, 01010010, 01001010, 82, 74
83, 01010011, 11001010, 83, -54
84, 01010100, 00101010, 84, 42
85, 01010101, 10101010, 85, -86
86, 01010110, 01101010, 86, 106
87, 01010111, 11101010, 87, -22
88, 01011000, 00011010, 88, 26
89, 01011001, 10011010, 89, -102
90, 01011010, 01011010, 90, 90
91, 01011011, 11011010, 91, -38
92, 01011100, 00111010, 92, 58
93, 01011101, 10111010, 93, -70
94, 01011110, 01111010, 94, 122
95, 01011111, 11111010, 95, -6
96, 01100000, 00000110, 96, 6
97, 01100001, 10000110, 97, -122
98, 01100010, 01000110, 98, 70
99, 01100011, 11000110, 99, -58
100, 01100100, 00100110, 100, 38
101, 01100101, 10100110, 101, -90
102, 01100110, 01100110, 102, 102
103, 01100111, 11100110, 103, -26
104, 01101000, 00010110, 104, 22
105, 01101001, 10010110, 105, -106
106, 01101010, 01010110, 106, 86
107, 01101011, 11010110, 107, -42
108, 01101100, 00110110, 108, 54
109, 01101101, 10110110, 109, -74
110, 01101110, 01110110, 110, 118
111, 01101111, 11110110, 111, -10
112, 01110000, 00001110, 112, 14
113, 01110001, 10001110, 113, -114
114, 01110010, 01001110, 114, 78
115, 01110011, 11001110, 115, -50
116, 01110100, 00101110, 116, 46
117, 01110101, 10101110, 117, -82
118, 01110110, 01101110, 118, 110
119, 01110111, 11101110, 119, -18
120, 01111000, 00011110, 120, 30
121, 01111001, 10011110, 121, -98
122, 01111010, 01011110, 122, 94
123, 01111011, 11011110, 123, -34
124, 01111100, 00111110, 124, 62
125, 01111101, 10111110, 125, -66
126, 01111110, 01111110, 126, 126
127, 01111111, 11111110, 127, -2
128, 10000000, 00000001, -128, 1
129, 10000001, 10000001, -127, -127
130, 10000010, 01000001, -126, 65
131, 10000011, 11000001, -125, -63
132, 10000100, 00100001, -124, 33
133, 10000101, 10100001, -123, -95
134, 10000110, 01100001, -122, 97
135, 10000111, 11100001, -121, -31
136, 10001000, 00010001, -120, 17
137, 10001001, 10010001, -119, -111
138, 10001010, 01010001, -118, 81
139, 10001011, 11010001, -117, -47
140, 10001100, 00110001, -116, 49
141, 10001101, 10110001, -115, -79
142, 10001110, 01110001, -114, 113
143, 10001111, 11110001, -113, -15
144, 10010000, 00001001, -112, 9
145, 10010001, 10001001, -111, -119
146, 10010010, 01001001, -110, 73
147, 10010011, 11001001, -109, -55
148, 10010100, 00101001, -108, 41
149, 10010101, 10101001, -107, -87
150, 10010110, 01101001, -106, 105
151, 10010111, 11101001, -105, -23
152, 10011000, 00011001, -104, 25
153, 10011001, 10011001, -103, -103
154, 10011010, 01011001, -102, 89
155, 10011011, 11011001, -101, -39
156, 10011100, 00111001, -100, 57
157, 10011101, 10111001, -99, -71
158, 10011110, 01111001, -98, 121
159, 10011111, 11111001, -97, -7
160, 10100000, 00000101, -96, 5
161, 10100001, 10000101, -95, -123
162, 10100010, 01000101, -94, 69
163, 10100011, 11000101, -93, -59
164, 10100100, 00100101, -92, 37
165, 10100101, 10100101, -91, -91
166, 10100110, 01100101, -90, 101
167, 10100111, 11100101, -89, -27
168, 10101000, 00010101, -88, 21
169, 10101001, 10010101, -87, -107
170, 10101010, 01010101, -86, 85
171, 10101011, 11010101, -85, -43
172, 10101100, 00110101, -84, 53
173, 10101101, 10110101, -83, -75
174, 10101110, 01110101, -82, 117
175, 10101111, 11110101, -81, -11
176, 10110000, 00001101, -80, 13
177, 10110001, 10001101, -79, -115
178, 10110010, 01001101, -78, 77
179, 10110011, 11001101, -77, -51
180, 10110100, 00101101, -76, 45
181, 10110101, 10101101, -75, -83
182, 10110110, 01101101, -74, 109
183, 10110111, 11101101, -73, -19
184, 10111000, 00011101, -72, 29
185, 10111001, 10011101, -71, -99
186, 10111010, 01011101, -70, 93
187, 10111011, 11011101, -69, -35
188, 10111100, 00111101, -68, 61
189, 10111101, 10111101, -67, -67
190, 10111110, 01111101, -66, 125
191, 10111111, 11111101, -65, -3
192, 11000000, 00000011, -64, 3
193, 11000001, 10000011, -63, -125
194, 11000010, 01000011, -62, 67
195, 11000011, 11000011, -61, -61
196, 11000100, 00100011, -60, 35
197, 11000101, 10100011, -59, -93
198, 11000110, 01100011, -58, 99
199, 11000111, 11100011, -57, -29
200, 11001000, 00010011, -56, 19
201, 11001001, 10010011, -55, -109
202, 11001010, 01010011, -54, 83
203, 11001011, 11010011, -53, -45
204, 11001100, 00110011, -52, 51
205, 11001101, 10110011, -51, -77
206, 11001110, 01110011, -50, 115
207, 11001111, 11110011, -49, -13
208, 11010000, 00001011, -48, 11
209, 11010001, 10001011, -47, -117
210, 11010010, 01001011, -46, 75
211, 11010011, 11001011, -45, -53
212, 11010100, 00101011, -44, 43
213, 11010101, 10101011, -43, -85
214, 11010110, 01101011, -42, 107
215, 11010111, 11101011, -41, -21
216, 11011000, 00011011, -40, 27
217, 11011001, 10011011, -39, -101
218, 11011010, 01011011, -38, 91
219, 11011011, 11011011, -37, -37
220, 11011100, 00111011, -36, 59
221, 11011101, 10111011, -35, -69
222, 11011110, 01111011, -34, 123
223, 11011111, 11111011, -33, -5
224, 11100000, 00000111, -32, 7
225, 11100001, 10000111, -31, -121
226, 11100010, 01000111, -30, 71
227, 11100011, 11000111, -29, -57
228, 11100100, 00100111, -28, 39
229, 11100101, 10100111, -27, -89
230, 11100110, 01100111, -26, 103
231, 11100111, 11100111, -25, -25
232, 11101000, 00010111, -24, 23
233, 11101001, 10010111, -23, -105
234, 11101010, 01010111, -22, 87
235, 11101011, 11010111, -21, -41
236, 11101100, 00110111, -20, 55
237, 11101101, 10110111, -19, -73
238, 11101110, 01110111, -18, 119
239, 11101111, 11110111, -17, -9
240, 11110000, 00001111, -16, 15
241, 11110001, 10001111, -15, -113
242, 11110010, 01001111, -14, 79
243, 11110011, 11001111, -13, -49
244, 11110100, 00101111, -12, 47
245, 11110101, 10101111, -11, -81
246, 11110110, 01101111, -10, 111
247, 11110111, 11101111, -9, -17
248, 11111000, 00011111, -8, 31
249, 11111001, 10011111, -7, -97
250, 11111010, 01011111, -6, 95
251, 11111011, 11011111, -5, -33
252, 11111100, 00111111, -4, 63
253, 11111101, 10111111, -3, -65
254, 11111110, 01111111, -2, 127
255, 11111111, 11111111, -1, -1
通过检查您可以看到这是正确的。特别是在 +/- 127/128 边界附近，其他一些答案是错误的。
到底是谁决定在 Java 中使用有符号字节？这确实是第一个邪恶。
这里是 Java 字节，按二进制表示形式排序（从 00000000 到 11111111）：
0、1、2、..、126、127、-128、-127、..、-2、-1
00000000 为 0，11111111 为 -1
反转 0 为 -1，反转 1 为 -2，...，反转 127 为 -128。 因此，如果你想反转 Java 字节的位，你应该得到具有相反符号的字节并减一：
byte myByte = 123;
byte myInvertedByte = -myByte-1;
private byte reverseBitsByte(byte x)
{
int intSize = 8;
byte y = 0;
for (int position = intSize - 1; position >= 0; position--)
{
y += ((x & 1) << position);
x >>= 1;
}
return y;
}