3.12. byte 类型

3.12. byte 类型
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3.12.1. string2byte

			
	byte[] bytes = "Helloworld!!! - http://www.netkiller.cn".getBytes();

3.12.2. 初始化 byte[] 填充数据 0

			
package cn.netkiller.test;

import java.util.Arrays;

public class Test {


    public static void main(String[] args) throws InterruptedException {

        byte[] buffer = new byte[16];
        Arrays.fill(buffer, (byte) 0); // 确保每个元素为 0

        System.out.println(Arrays.toString(buffer));

    }

}

3.12.3. byte[] to String

			
	byte[] bytes = "Helloworld!!! - http://www.netkiller.cn".getBytes();
	String str = new String(bytes, StandardCharsets.UTF_8);
	System.out.println(str);

3.12.4. BigInteger2byte

			
BigInteger b= new BigInteger('300');
byte bytes= b.byteValue();

3.12.5. int to byte array

			
int a= 120;
byte b= (byte)a;

			
private byte[] bigIntToByteArray( final int i ) {
    BigInteger bigInt = BigInteger.valueOf(i);      
    return bigInt.toByteArray();
}

			
private byte[] intToByteArray ( final int i ) throws IOException {      
    ByteArrayOutputStream bos = new ByteArrayOutputStream();
    DataOutputStream dos = new DataOutputStream(bos);
    dos.writeInt(i);
    dos.flush();
    return bos.toByteArray();
}

			
private byte[] intToBytes( final int i ) {
    ByteBuffer bb = ByteBuffer.allocate(4); 
    bb.putInt(i); 
    return bb.array();
}

位移操作

			
private static byte[] intToBytes(final int a) {
    return new byte[] {
        (byte)((data >> 24) & 0xff),
        (byte)((data >> 16) & 0xff),
        (byte)((data >> 8) & 0xff),
        (byte)((data >> 0) & 0xff),
    };
}

3.12.6. byte array to int

			
private int convertByteArrayToInt(byte[] intBytes){
    ByteBuffer byteBuffer = ByteBuffer.wrap(intBytes);
    return byteBuffer.getInt();
}

			
private int convertByteArrayToInt(byte[] data) {
    if (data == null || data.length != 4) return 0x0;
    // ----------
    return (int)( // NOTE: type cast not necessary for int
            (0xff & data[0]) << 24  |
            (0xff & data[1]) << 16  |
            (0xff & data[2]) << 8   |
            (0xff & data[3]) << 0
            );
}

			
	public static byte[] intToByte32(int num) {
        byte[] arr = new byte[32];
        for (int i = 31; i >= 0; i--) {
            // &1 也可以改为num&0x01,表示取最地位数字.
            arr[i] = (byte) (num & 1);
            // 右移一位.
            num >>= 1;
        }
        return arr;
    }

			
	public static int byte32ToInt(byte[] arr) {
        if (arr == null || arr.length != 32) {
            throw new IllegalArgumentException("byte数组必须不为空,并且长度是32!");
        }
        int sum = 0;
        for (int i = 0; i < 32; ++i) {
            sum |= (arr[i] << (31 - i));
        }
        return sum;
    }

int array to byte array

			
private byte[] convertIntArrayToByteArray(int[] data) {
        if (data == null) return null;
        // ----------
        byte[] byts = new byte[data.length * 4];
        for (int i = 0; i < data.length; i++)
            System.arraycopy(convertIntToByteArray(data[i]), 0, byts, i * 4, 4);
        return byts;
    }

byte array to int array

			
public int[] convertByteArrayToIntArray(byte[] data) {
        if (data == null || data.length % 4 != 0) return null;
        // ----------
        int[] ints = new int[data.length / 4];
        for (int i = 0; i < ints.length; i++)
            ints[i] = ( convertByteArrayToInt(new byte[] {
                    data[(i*4)],
                    data[(i*4)+1],
                    data[(i*4)+2],
                    data[(i*4)+3],
            } ));
        return ints;
    }

3.12.7. byte2char

			
	byte b1 = 65;
    // char ch = b1;  
          
    char ch = (char) b1;
 
    System.out.println("byte value: " + b1);             // prints 65
    System.out.println("Converted char value: " + ch);   // prints A (ASCII is 65 for A)

			
	public static char byte2ToChar(byte[] arr) {
        if (arr == null || arr.length != 2) {
            throw new IllegalArgumentException("byte数组必须不为空,并且是2位!");
        }
        return (char) (((char) (arr[0] << 8)) | ((char) arr[1]));
    }			
    
    public static byte[] charToByte2(char c) {
        byte[] arr = new byte[2];
        arr[0] = (byte) (c >> 8);
        arr[1] = (byte) (c & 0xff);
        return arr;
    }

3.12.8. longToByte64

			
    public static byte[] longToByte64(long sum) {
        byte[] arr = new byte[64];
        for (int i = 63; i >= 0; i--) {
            arr[i] = (byte) (sum & 1);
            sum >>= 1;
        }
        return arr;
    }

3.12.9. byte64ToLong

			
	public static long byte8ToLong(byte[] arr) {
        if (arr == null || arr.length != 8) {
            throw new IllegalArgumentException("byte数组必须不为空,并且是8位!");
        }
        return (long) (((long) (arr[0] & 0xff) << 56) | ((long) (arr[1] & 0xff) << 48) | ((long) (arr[2] & 0xff) << 40)
                        | ((long) (arr[3] & 0xff) << 32) | ((long) (arr[4] & 0xff) << 24)
                        | ((long) (arr[5] & 0xff) << 16) | ((long) (arr[6] & 0xff) << 8) | ((long) (arr[7] & 0xff)));
    }
    			
	public static byte[] longToByte8(long sum) {
        byte[] arr = new byte[8];
        arr[0] = (byte) (sum >> 56);
        arr[1] = (byte) (sum >> 48);
        arr[2] = (byte) (sum >> 40);
        arr[3] = (byte) (sum >> 32);
        arr[4] = (byte) (sum >> 24);
        arr[5] = (byte) (sum >> 16);
        arr[6] = (byte) (sum >> 8);
        arr[7] = (byte) (sum & 0xff);
        return arr;
    }
    			
	public static long byte64ToLong(byte[] arr) {
        if (arr == null || arr.length != 64) {
            throw new IllegalArgumentException("byte数组必须不为空,并且长度是64!");
        }
        long sum = 0L;
        for (int i = 0; i < 64; ++i) {
            sum |= ((long) arr[i] << (63 - i));
        }
        return sum;
    }

3.12.10. short2byte

			
    public static byte[] shortToByte16(short s) {
        byte[] arr = new byte[16];
        for (int i = 15; i >= 0; i--) {
            arr[i] = (byte) (s & 1);
            s >>= 1;
        }
        return arr;
    }

    public static short byte16ToShort(byte[] arr) {
        if (arr == null || arr.length != 16) {
            throw new IllegalArgumentException("byte数组必须不为空,并且长度为16!");
        }
        short sum = 0;
        for (int i = 0; i < 16; ++i) {
            sum |= (arr[i] << (15 - i));
        }
        return sum;
    }			
    
    public static short byte2ToShort(byte[] arr) {
        if (arr != null && arr.length != 2) {
            throw new IllegalArgumentException("byte数组必须不为空,并且是2位!");
        }
        return (short) (((short) arr[0] << 8) | ((short) arr[1] & 0xff));
    }
    
    public static byte[] shortToByte2(Short s) {
        byte[] arr = new byte[2];
        arr[0] = (byte) (s >> 8);
        arr[1] = (byte) (s & 0xff);
        return arr;
    }

3.12.11. byte8ToDouble

			
	public static double byte8ToDouble(byte[] arr) {
        if (arr == null || arr.length != 8) {
            throw new IllegalArgumentException("byte数组必须不为空,并且是8位!");
        }
        long l = byte8ToLong(arr);
        return Double.longBitsToDouble(l);
    }

    public static byte[] doubleToByte8(double i) {
        long j = Double.doubleToLongBits(i);
        return longToByte8(j);
    }

3.12.12. byte4ToFloat

			
    public static float byte4ToFloat(byte[] arr) {
        if (arr == null || arr.length != 4) {
            throw new IllegalArgumentException("byte数组必须不为空,并且是4位!");
        }
        int i = byte4ToInt(arr);
        return Float.intBitsToFloat(i);
    }

    public static byte[] floatToByte4(float f) {
        int i = Float.floatToIntBits(f);
        return intToByte4(i);
    }

3.12.13. 无符号 byte

			
byte b= -120;
int a= bytes & 0xff;

			
byte a = (byte)234;
System.out.println(a);

上面的代码，结果是-22，因为java中byte是有符号的，byte范围是-128~127。

如果想输出234，该怎么做呢，首先想到的是将a 赋给大一点的类型，如下：

byte a = (byte)234;
int i = a&0xff;
System.out.println(i);

原因是 0xff是int，占4个字节，a是byte，占1个字节，进行&操作的细节如下：

   00000000 00000000 00000000 11101010    (a)
&
   00000000 00000000 00000000 11111111    (0xff)
---------------------------------------------------------------------
=  00000000 00000000 00000000 11101010

结果是int，但是符号位是0，说明是正数，最后就是正整数234.

3.12.14. byte to hex

			
byte bv = 10;
String hexString = Integer.toHexString(bv);

3.12.15. byte[] to hex

			
byte bytes[] = {(byte)0, (byte)0, (byte)134, (byte)0, (byte)61};
System.out.println(javax.xml.bind.DatatypeConverter.printHexBinary(bytes));

			
public static String byteArrayToHex(byte[] bytes) {
   StringBuilder sb = new StringBuilder(a.length * 2);
   for(byte b: bytes)
      sb.append(String.format("%02x", b));
   return sb.toString();
}

			
BigInteger n = new BigInteger(byteArray);
String hexa = n.toString(16));

3.12.16. 连接两个 byte[]

			
byte[] one = { 1, 2, 3 };
byte[] two = { 6, 8, 9 };
int length = one.Length + two.Length;
byte[] sum = new byte[length];
one.CopyTo(sum,0);
two.CopyTo(sum,one.Length);

			
byte[] one = { 1, 2, 3 };
byte[] two = { 6, 8, 9 };
List<byte> list1 = new List<byte>(one);
List<byte> list2 = new List<byte>(two);
list1.AddRange(list2);
byte[] sum2 = list1.ToArray();

3.12.17. List<Byte> to byte[]

			
		List<Byte> byteList = new ArrayList<Byte>();
        byteList.add((byte) 1);
        byteList.add((byte) 2);
        byteList.add((byte) 3);
        byte[] byteArray = Bytes.toArray(byteList);
        System.out.println(Arrays.toString(byteArray));

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