Mock Data Generator — Java source

// mock-data-generator — Java port of the CosmoDev tool.
// The seeded mulberry32 PRNG (bit-identical to src/lib/mockData.ts and the Go
// twin) drives a representative field set; int arithmetic already wraps mod
// 2^32 (the Math.imul semantics) and >>> supplies the unsigned shift.
import java.util.LinkedHashMap;
import java.util.Map;

public class MockDataGenerator {

    static final String[] FIRST =
        { "Ava", "Liam", "Noah", "Emma", "Olivia", "Aiden", "Sophia", "Mason" };
    static final String[] LAST =
        { "Smith", "Johnson", "Williams", "Brown", "Jones", "Garcia", "Miller", "Davis" };

    /** PRNG with carried state so draws stay in schema order (the TS closure). */
    static final class Rng {
        private int a;
        Rng(int seed) { this.a = seed; }
        double next() {
            a += 0x6D2B79F5;                                   // wraps: int is mod 2^32
            int t = (a ^ (a >>> 15)) * (1 | a);                // == Math.imul here
            t = (t + (t ^ (t >>> 7)) * (61 | t)) ^ t;
            return ((t ^ (t >>> 14)) & 0xFFFFFFFFL) / 4294967296.0; // unsigned
        }
    }

    /** Representative fields from the schema dispatch in mockData.ts. */
    static Object field(String type, int index, Rng rng, int min, int max) {
        switch (type) {
            case "index":
                return index; // no draw
            case "email": {   // two draws, like TS
                String f = FIRST[(int) (rng.next() * FIRST.length)].toLowerCase();
                String l = LAST[(int) (rng.next() * LAST.length)].toLowerCase();
                return f + "." + l + "@example.com";
            }
            case "integer":
                return min + (int) (rng.next() * (max - min + 1));
            case "boolean":
                return rng.next() < 0.5;
            default:
                return null; // unknown type -> null
        }
    }

    public static void main(String[] args) {
        Rng rng = new Rng(1234); // seed
        String[][] schema = {    // name, type, min, max
            { "id", "index", "0", "0" },
            { "email", "email", "0", "0" },
            { "age", "integer", "18", "65" },
            { "active", "boolean", "0", "0" },
        };

        for (int i = 0; i < 3; i++) { // count
            Map<String, Object> row = new LinkedHashMap<>(); // insertion order
            for (String[] spec : schema)
                row.put(spec[0], field(spec[1], i, rng,
                        Integer.parseInt(spec[2]), Integer.parseInt(spec[3])));
            System.out.println(row);
        }
    }
}