public static void main(String[] args) {
        int binary = 4;
        int  hexadecimal = 43;

        //Convert the integer to binary. Stored in String.
        String bin =  Integer.toBinaryString(binary);
        System.out.println(binary + " as binary: " +  bin);

        //Convert the second integer into hex. Stored in String.
        String hex =  Integer.toHexString(hexadecimal);
        System.out.println(hexadecimal + " as hex:  " + hex);

        //To convert back, parse the String with base 2  (binary).
        System.out.println(bin + " as integer: " + Integer.parseInt(bin,  2));

        //Hexadecimal is base-16, so pass in 16 as base.
        System.out.println(hex +  " as integer: " + Integer.parseInt(hex, 16));
    }

Just paste these java codes in your java file .Compile and Run it .

Now u will be able to easily convert the Number System to each other in java