Convert hex string to binary string

You need to tell Java that the int is in hex, like this:

String hexToBinary(String hex) {
    int i = Integer.parseInt(hex, 16);
    String bin = Integer.toBinaryString(i);
    return bin;
}

the accepted version will only work for 32 bit numbers.

Here's a version that works for arbitrarily long hex strings:

public static String hexToBinary(String hex) {
    return new BigInteger(hex, 16).toString(2);
}

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