Varargs and Method Overloading

import java.util.*;
import java.util.stream.Collectors;

public class VarargsDemo {

    // Basic varargs
    static int sum(int... numbers) {
        int total = 0;
        for (int n : numbers) total += n;
        return total;
    }

    // Varargs with required first param
    static String join(String separator, String... parts) {
        return String.join(separator, parts);
    }

    // Type-safe heterogeneous container
    @SafeVarargs
    static <T> List<T> listOf(T... items) {
        return List.of(items);
    }

    // Printf-style formatting
    static void log(String format, Object... args) {
        String timestamp = java.time.LocalTime.now().toString();
        System.out.printf("[%s] %s%n", timestamp, String.format(format, args));
    }

    // Builder with varargs
    static class Query {
        private final String table;
        private final List<String> columns;
        private final List<String> conditions;

        private Query(String table, List<String> columns, List<String> conditions) {
            this.table = table;
            this.columns = columns;
            this.conditions = conditions;
        }

        static Query from(String table) {
            return new Query(table, List.of("*"), List.of());
        }

        Query select(String... cols) {
            return new Query(table, List.of(cols), conditions);
        }

        Query where(String... conds) {
            var all = new ArrayList<>(conditions);
            all.addAll(List.of(conds));
            return new Query(table, columns, all);
        }

        String build() {
            String sql = "SELECT " + String.join(", ", columns) + " FROM " + table;
            if (!conditions.isEmpty()) {
                sql += " WHERE " + String.join(" AND ", conditions);
            }
            return sql;
        }
    }

    // Overloading with varargs
    static String format(String value) { return value; }
    static String format(String value, int width) {
        return String.format("%" + width + "s", value);
    }
    static String format(String value, int width, char fill) {
        String padded = format(value, width);
        return padded.replace(' ', fill);
    }

    public static void main(String[] args) {
        System.out.println(sum(1, 2, 3, 4, 5));     // 15
        System.out.println(sum());                    // 0
        System.out.println(join("-", "a", "b", "c")); // a-b-c

        log("User %s logged in from %s", "alice", "192.168.1.1");

        // Query builder
        String sql = Query.from("users")
            .select("name", "email", "age")
            .where("age > 18", "active = true")
            .build();
        System.out.println(sql);

        // Overloaded
        System.out.println(format("hi", 10, '.'));  // ........hi
    }
}