CODEWITHSUNDEEP
javaarraysbytelong-integer
Rahul Baradia
Rahul Baradia

Reputation: 11951

concatenate long and bytearray to another bytearray

I am trying to concatenate long and bytearray to another bytearray.

I tried like this :

byte[] value1= new byte[16];
byte[] value2= new byte[16];
byte[] finalvalue = new byte[value1.length + value2.length];
long ts = System.currentTimeMillis();
int val = 100;

ByteBuffer.wrap(value1).order(ByteOrder.LITTLE_ENDIAN).asLongBuffer().put(ts);
ByteBuffer.wrap(value2).order(ByteOrder.LITTLE_ENDIAN).asIntBuffer().put(val);

System.arraycopy(value1, 0, finalvalue, 0, value1.length);
System.arraycopy(value2, 0, finalvalue, value1.length,value2.length);

When I tried to print this, I am not getting the correct values. It printing like this 

BYTEVALUE -95-15-4410659100000000002000000000000000

it should print like this 

- BYTEVALUE- 1354707038625,100

Can anyone help me out where I am going wrong.

Help will be appreciated.

Update:

Use to print values using StringBuffer like this:

StringBuffer sb = new StringBuffer(finalvalue.length);
for (int i = 0; i < finalvalue.length; i++) {
  sb.append(finalvalue[i]);
}

Upvotes: 0

Views: 184

Answers (1)

Duncan Jones
Duncan Jones

Reputation: 69339

Your code is not doing what you think it is. Consider the following self-contained application:

import java.nio.ByteBuffer;
import java.nio.ByteOrder;

public class ByteArrayTest {

  public static void main(String[] args) {
    byte[] value1 = new byte[16];
    byte[] value2 = new byte[16];
    byte[] finalvalue = new byte[value1.length + value2.length];
    long ts = System.currentTimeMillis();
    int val = 100;

    ByteBuffer.wrap(value1).order(ByteOrder.LITTLE_ENDIAN).asLongBuffer()
        .put(ts);
    ByteBuffer.wrap(value2).order(ByteOrder.LITTLE_ENDIAN).asIntBuffer()
        .put(val);

    System.arraycopy(value1, 0, finalvalue, 0, value1.length);
    System.arraycopy(value2, 0, finalvalue, value1.length, value2.length);

    printByteArray(finalvalue);
  }

  private static void printByteArray(final byte[] array) {
    StringBuilder sb = new StringBuilder(array.length);
    for (byte b : array) {
      sb.append(String.format("%02X", b));
    }
    System.out.println(sb.toString());
  }
}

The output of this is:

BE26086B3B010000000000000000000064000000000000000000000000000000

Splitting this into component parts, we can see why:

  • The first sixteen bytes are BE26086B3B0100000000000000000000. This is your timestamp in little endian order. If you ignore the zero bytes, this converts to 1,354,710,394,558 in decimal, which is correct.

  • The second sixteen bytes are 64000000000000000000000000000000, which is your hard-coded value 100.

The zeroes represent the space in the byte arrays that you didn't use.

Upvotes: 2

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