java中的byte运算

package test;public class A {public static void main(String[] args) {//前提：在java中，默认都是int型//负数在计算机中用补码表示，转换规则为//十进求二进制负数情况//先求出与该负数相对应正整数二进制代码，然后所有位取反（不管符号位），末尾加1，不够位数时左边补1。//二进制求十进制负数情况//如果首位是1，表明是负整数。将所有位取反（不管符号位），末尾加1，所得数字就是该负数的绝对值。System.out.println((byte) -129); // 结果显示127// 129的二进制 为 1000 0001，因为是-129，根据补码运算规则，得到-129的补码表示 0111 1111，因此计算结果显示为127byte t = -120;  //120的二进制为 0111 1000，因为为(-120)，根据补码运算得到1000 1000，这是在计算机内部的表示System.out.println(Integer.toBinaryString(t)); // t转为整形，因为1000 1000为负数，所以需要在前面补充1， 显示结果为：1111111111111111111111110001000int t2 = (byte) 136 & 0xff; //运算步骤，136在java中默认是int类型，为  00000000 00000000 00000000 10001000，强制转为byte后，为1000 1000，//与  0xff 运算后(0xff为int类型)，又变成int类型 00000000 00000000 00000000 10001000System.out.println((byte) t2); // 强制转换后为 1000 1000，因为是负数，根据补码的表示规则为 0111 1000，为120，因为原始为负数，所以结果为-120System.out.println(t2 + " " + Integer.toBinaryString(t2)); // 显示结果为 136 10001000，说明如果是证书，int前面的0不显示 }// 整形转byte数组public static byte[] int2Bytes(int a) {byte[] b = new byte[4];b[0] = (byte) (a >> 24);b[1] = (byte) (a >> 16);b[2] = (byte) (a >> 8);b[3] = (byte) (a);return b;}public static int bytes2Int(byte[] b) {return ((b[0] & 0xff) << 24) | ((b[1] & 0xff) << 16)| ((b[2] & 0xff) << 8) | (b[3] & 0xff);}}

工具函数：

/** * java basic number types: * long => 64 -9,223,372,036,854,775,808 ~ 9,223,372,036,854,775,807  * int  => 32 -2,147,483,648 ~ 2,147,483,647  * short=> 16 -32,768 ~ 32,767  * byte =>  8 -128~127 */public class Test {private static char[] hex_chars = new char[]{'0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'};private static int ONE_BYTE_MASK = 0XFF; //255//byte数组填充0public static void fillWithNUL(byte[] b){for(int i=0; i<b.length; ++i){b[i] = 0x00; //16进制表示}}//byte数组逆序public static byte[] reverse(byte[] b){byte[] b1 = new byte[b.length];int index = 0;for(int i=b.length-1; i>=0; --i){b1[index] = b[i];++index;}return b1;}//两个数组是否相等public static boolean byteArrayEquals(byte[] array1,int array1off,byte[] array2,int array2off,int len){    for (int i = 0; i < len; ++i)    if (array1[array1off+i] != array2[array2off+i])    return false;    return true;}//byte转成intpublic static int onebyte2int(byte[] b, int off){return (0xFF & b[off]); //0xFF java数字默认是int类型的}//int型转为bytepublic static void int2onebyte(int n, byte[] b, int off) throws Exception{if(!(n>=0 && n<=255)) throw new Exception(n+" exceed unsigned char range [0,255]!");b[off] = 0x00;b[off] |= n;}//两个byte转成intpublic static int twobyte2int(byte[] b, int off){int n = 0;n |= ( 0xFF & b[off] ) << 8;n |= ( 0xFF & b[off+1] );return n;}//int转为bytepublic static void int2twobyte(int n, byte[] b, int off) throws Exception{if(!(n>=0 && n<=65535)) throw new Exception(n+" exceed unsigned short int range [0,65535]!");b[off]   = 0x00;b[off+1] = 0x00;b[off]   |= (n >> 8);b[off+1] |= n;}//三组byte转为整形public static int threebyte2int(byte[] b, int off){int n = 0;n |= ( 0xFF & b[off] )   << 16;n |= ( 0xFF & b[off+1] ) << 8;n |= ( 0xFF & b[off+2] );return n;}//int转为三组bytepublic static void int2threebyte(int n, byte[] b, int off) throws Exception{if(!(n>=0 && n<=0xFFFFFF)) throw new Exception(n+" exceed unsigned short int range [0,16777215]!");b[off]   = 0x00;b[off+1] = 0x00;b[off+2] = 0x00;b[off]   |= (n >> 16);b[off+1] |= (n >> 8);b[off+2] |= n;}//4组byte转成longpublic static long fourbyte2long(byte[] b, int off){long n = 0L;n |= ( 0xFFL & b[off] )   << 24;n |= ( 0xFFL & b[off+1] ) << 16;n |= ( 0xFFL & b[off+2] ) << 8;n |= ( 0xFFL & b[off+3] );return n;}//long转到4个数组中public static void long2fourbyte(long n, byte[] b, int off) throws Exception{if(!(n>=0 && n<=4294967295L)) throw new Exception(n+" exceed unsigned long int range [0,4294967295]!");b[off]   = 0x00;b[off+1] = 0x00;b[off+2] = 0x00;b[off+3] = 0x00;b[off]   |= (n >> 24);b[off+1] |= (n >> 16);b[off+2] |= (n >> 8);b[off+3] |= n;}//四组byte转intpublic static int byte2int(byte[] b){if(b==null || b.length!=4) return -1;int mask = 0xff;int temp = 0;int res = 0;for (int i = 0; i < 4; i++) {res <<= 8; //左移8位，为0不变temp = b[i] & mask;res |= temp;}return res;}//int转为byte数组public static byte[] int2byte(int n) {int mask = 0xff;byte[] b = new byte[4];b[3] = (byte)(n & mask); //强转 b[2] = (byte)(n >> 8 & mask);b[1] = (byte)(n >> 16 & mask);b[0] = (byte)(n >> 24 & mask);return b;}//byte转shortpublic static short byte2short(byte[] b) {if(b==null || b.length!=2) return -1;int mask = 0xff;int temp = 0;short res = 0;for (int i = 0; i < 2; i++) {res <<= 8;temp = b[i] & mask;res |= temp;}return res;}//short转为bytepublic static byte[] short2byte(short n) {byte[] b = new byte[2];b[1] = (byte)(n & 0xff);b[0] = (byte)(n >> 8 & 0xff);return b;}//数组拷贝public byte[] subArray(byte[] byte_array,int off,int len){byte[] result = new byte[len];System.arraycopy(byte_array, off, result, 0, len); //源数组，起始位置，目的数组，起始位置，长度return result;}//byte数组转为16进制，利用 hex_chars 数组public static String byte2hex(byte[] byte_array,int off,int len){StringBuilder sb = new StringBuilder();for(int i=off; i<off+len; ++i){byte temp = byte_array[i];sb.append( hex_chars[ temp>>>4 & 0X0F ] ); //无符号右移，左侧补0sb.append( hex_chars[ temp & 0X0F ] );}return sb.toString();}public static String byte2hex(byte[] byte_array){StringBuilder sb = new StringBuilder();for(int i=0; i<byte_array.length; ++i){byte temp = byte_array[i];sb.append( hex_chars[ temp>>>4 & 0X0F ] );sb.append( hex_chars[ temp & 0X0F ] );}return sb.toString();}public static String byte2hexWithBlank(byte[] byte_array){if(byte_array==null) return "";StringBuilder sb = new StringBuilder();for(int i=0; i<byte_array.length; ++i){byte temp = byte_array[i];sb.append( hex_chars[ temp>>>4 & 0X0F ] );sb.append( hex_chars[ temp & 0X0F ] );sb.append(" ");}return sb.toString();}//16进制字符串转byte数组public static byte[] hex2byte(String hexString) throws Exception{byte[] hexStrBytes = hexString.getBytes();if(hexStrBytes.length % 2 != 0) throw new IllegalArgumentException("["+hexString+"] lengh is even");byte[] bytes = new byte[hexStrBytes.length/2];for(int i=0; i<hexStrBytes.length; i+=2 ){String item = new String(hexStrBytes,i,2);int2onebyte(Integer.parseInt(item,16),bytes,i/2); }return bytes;}public static byte[] hex2byteWithBlank(String hexStringWithBlank) throws Exception{hexStringWithBlank = hexStringWithBlank.replaceAll(" ", "");return hex2byte(hexStringWithBlank);}//两个数组是否相等public static boolean equals(byte[] b1,byte[] b2){return Arrays.equals(b1, b2);}//public static String revertStringFromBytes(byte[] ba){int index = 0;for(int i=0; i<ba.length; ++i){if(ba[i]=='\0'){index = i;break;}}return new String(ba,0,index); //转为}public static void main(String[] args) throws Exception{int i=10;System.out.println("10转16进制=="+Integer.toHexString(i)); //a，返回的都是strSystem.out.println("10转8进制=="+Integer.toOctalString(i)); //12System.out.println("10转2进制=="+Integer.toBinaryString(i)); //1010String str1 = "A";System.out.println("16转10进制=="+Integer.parseInt(str1, 16)); //10 结果是intString str2 = "12";System.out.println("16转10进制=="+Integer.parseInt(str2, 8)); //10 结果是intString str3 = "1010";System.out.println("16转10进制=="+Integer.parseInt(str3, 2)); //10 结果是int}}