This code demonstrates how it's possible to compress two numbers into one and then convert it back to two numbers.

TwoNumbersCompression.java

public class TwoNumbersCompression {
    public static void main(String[] args) {
        double compressed = compress(-5.57,8);
        System.out.println("Compressed: " + compressed);
        double[] decompressed = decompress(compressed);
        System.out.println("Decompressed: " + decompressed[0] + ", " + decompressed[1]);
    }

    // Convert to between 0 and 1
    public static double convert(double a) {
        // 0.5 + tan^-1(a) / pi
        return 0.5 + Math.atan(a) / Math.PI;
    }

    // Convert back to original number
    public static double convertBack(double a) {
        // tan(pi * (a - 0.5))
        return Math.tan(Math.PI * (a - 0.5));
    }

    // Compress two numbers into one
    public static double compress(double a, double b) {
        double a1 = convert(a);
        double b1 = convert(b);

        // Compression algorithm
        // (0.abcde, 0.fghij) -> 0.afbgchdiej
        // Explanation: a and f are the first digits, b and g are the second, etc.
        
        // Convert a1 to string
        String a1s = Double.toString(a1);
        // Convert b1 to string
        String b1s = Double.toString(b1);

        // Remove the 0. from the beginning of the strings
        a1s = a1s.substring(2);
        b1s = b1s.substring(2);

        // Create a new string to store the compressed number
        String c = "0.";

        // Loop through the strings
        for (int i = 0; i < Math.min(a1s.length(), b1s.length()); i++) {
            // Add the first digit of a1s to c
            c += a1s.charAt(i);
            // Add the first digit of b1s to c
            c += b1s.charAt(i);
        }

        // Convert c to a double and return it
        return Double.parseDouble(c);
    }

    // Decompress a number into two numbers
    public static double[] decompress(double c) {
        // Convert c to string
        String cs = Double.toString(c);

        // Remove the 0. from the beginning of the string
        cs = cs.substring(2);

        // Create two new strings to store the decompressed numbers
        String a1s = "0.";
        String b1s = "0.";

        // Loop through the string
        for (int i = 0; i < cs.length(); i++) {
            // If i is even, add the digit to a1s
            if (i % 2 == 0) {
                a1s += cs.charAt(i);
            }
            // If i is odd, add the digit to b1s
            else {
                b1s += cs.charAt(i);
            }
        }

        // Convert a1s and b1s to doubles
        double a1 = Double.parseDouble(a1s);
        double b1 = Double.parseDouble(b1s);

        // Convert a1 and b1 back to the original numbers
        double a = convertBack(a1);
        double b = convertBack(b1);

        // Round the numbers to 5 decimal places
        a = Math.round(a * 100000) / 100000.0;
        b = Math.round(b * 100000) / 100000.0;

        // Return the decompressed numbers
        return new double[] {a, b};
    }
}