JDBC

import java.sql.*;

// Connect to database
try (Connection conn = DriverManager.getConnection(
        "jdbc:postgresql://localhost:5432/mydb", "user", "pass")) {

    // Query
    try (PreparedStatement stmt = conn.prepareStatement(
            "SELECT id, name FROM users WHERE age > ?")) {
        stmt.setInt(1, 18);
        try (ResultSet rs = stmt.executeQuery()) {
            while (rs.next()) {
                int id = rs.getInt("id");
                String name = rs.getString("name");
                System.out.println(id + ": " + name);
            }
        }
    }

    // Transaction
    conn.setAutoCommit(false);
    try (PreparedStatement stmt = conn.prepareStatement(
            "UPDATE accounts SET balance = balance - ? WHERE id = ?")) {
        stmt.setInt(1, 100);
        stmt.setInt(2, 1);
        stmt.executeUpdate();
        conn.commit();
    } catch (SQLException e) {
        conn.rollback();
    }
}