What is the simple method two concatenate two byte arrays in Java? I used this function but got an error:
java.lang.ArrayIndexOutOfBoundsException: 16
My function is:
public static byte[] concatinate(byte[] a, byte[] b) {
byte[] c = new byte[100];
for (int i = 0; i < (a.length + b.length); i++) {
if (i < a.length) {
c[i] = a[i];
} else {
c[i] = b[i];
}
}
return c;
}
Firstly, your code is bound to fail if a.length + b.length > 100. You should be using a.length + b.length as the length of c.
Yes, because when you've gone past a.length, you're still trying to use b[i]. Imagine a.length is 50 and b.length is 1. You've got 51 array elements to populate, but to populate c[50] you need b[0], not b[50].
All you need to change is this:
c[i] = b[i];
To this:
c[i] = b[i - a.length];
... or have two loops instead, as per Mureinik's answer. (I wouldn't expect either option to be significantly faster than the other, and they're definitely equivalent - you can use whichever you find most readable.)
However, I'd recommend using System.arraycopy instead:
public static byte[] concatenate(byte[] a, byte[] b) {
byte[] c = new byte[a.length + b.length];
System.arraycopy(a, 0, c, 0, a.length);
System.arraycopy(b, 0, c, a.length, b.length);
return c;
}
Much simpler :)
i is less than a.length, it'll copy the value from a. If i is a.length or greater, it'll copy the value from b. A total of a.length + b.length elements are copied, which is correct. Where's the problem?i == a.length, then b[i - a.length] is b[0]. I suggest you work this through on a piece of paper with an example. It really is fine...Just define an array the size of the combined two arrays, and iterate each of them individually:
public static byte[] concatinate(byte[] a, byte[] b) {
byte[] c = new byte[a.length + b.length];
for (int i = 0; i < a.length; i++) {
c[i] = a[i];
}
for (int i = 0; i < b.length; i++) {
c[a.length + i] = b[i];
}
return c;
}
The code for appending 2 byte[] was good.If you want to keep on appending the byte[] you can use this code....
byte[] readBytes ; // Your byte array .... //for eg. readBytes = "TestBytes".getBytes();
ByteArrayBuffer mReadBuffer = new ByteArrayBuffer(0 ) ; // Instead of 0, if you know the count of expected number of bytes, nice to input here
mReadBuffer.append(readBytes, 0, readBytes.length); // this copies all bytes from readBytes byte array into mReadBuffer // Any new entry of readBytes, you can just append here by repeating the same call.
// Finally, if you want the result into byte[] form: byte[] result = mReadBuffer.buffer();
i > b.length, will cause this exception.