How to convert binary string to binary byte array in Java

Question

I have binary string like this: String a = "100100". I need to have binary byte array: byte[] b = {1,0,0,1,0,0} for output.

This is my code:

    String a="100100";

    byte[] b = null;
    for (int i = 0; i < a.length(); i++) {
        b[i]=a.charAt(i)=='1'? (byte) 1: (byte) 0;
        System.out.println("b["+i+"]: "+b[i]);
    }

But this approach is not working when i run it. Can any one give a correction? Thank you

Answer 1

byte[] is not initialized. So we need to initialize before we use it .

byte[] b = new byte[a.length()];

try this

Answer 2

You haven't assigned a value to your byte[] b, hence resulting in a NullPointerException, since you later reference it by index.

Try this instead:

String a="100100";

byte[] b = new byte[a.length()]; // here
for (int i = 0; i < a.length(); i++) {
    b[i]=a.charAt(i)=='1'? (byte) 1: (byte) 0;
}
System.out.println(Arrays.toString(b)); // easier print once finished

Output

[1, 0, 0, 1, 0, 0]