Checking individual bits in a byte array in Java?

Question

So say I have a byte array, and I have a function that checks whether the n-th least significant bit index of the byte array is a 1 or a 0. The function returns true if the bit is a 1 and false if the bit is a 0. The least significant bit of the byte array is defined as the last significant bit in the 0th index of the byte array, and the most significant bit of the byte array is defined as the most significant bit in the (byte array.length - 1)th index of the byte array.

For instance,

byte[] myArray = new byte[2];
byte[0] = 0b01111111;
byte[1] = 0b00001010;

Calling:

myFunction(0) = true;
myFunction(1) = true;
myFunction(7) = false;
myFunction(8) = false;
myFunction(9) = true;
myFunction(10) = false;
myFunction(11) = true;

What is the best way to do this?

Thanks!

Possible duplicate of How to get the value of a bit at a certain position from a byte? — Martin Schröder
– Martin Schröder, Commented May 29, 2017 at 14:08
@MartinSchröder first - necroposting, second - no, it's definitely different, here he requires byte[] — Andrii Plotnikov
– Andrii Plotnikov, Commented Nov 23, 2017 at 14:57

Rohit Jain · Accepted Answer · 2013-09-21 10:15:09Z

20

You can use this method:

public boolean isSet(byte[] arr, int bit) {
    int index = bit / 8;  // Get the index of the array for the byte with this bit
    int bitPosition = bit % 8;  // Position of this bit in a byte

    return (arr[index] >> bitPosition & 1) == 1;
}

bit % 8 is the bit position relative to a byte.
arr[index] >> bit % 8 moves the bit at index to bit 0 position.

edited Sep 21, 2013 at 10:15

answered Sep 21, 2013 at 10:09

Rohit Jain

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