JDBC
1. What Is JDBC? (beginner)
JDBC (java.sql) = Java's USB for databases (one API, any DB!). Drivers translate to MySQL/Oracle dialect. Steps mantra: Load → Connect → Statement → Result → Close!
2. Five Steps (exam code — memorize!)
import java.sql.*;
public class Jdbc {
public static void main(String[] args) throws Exception {
// 1. LOAD driver (registers!)
Class.forName("com.mysql.cj.jdbc.Driver");
// 2. CONNECT (url + user + pass!)
Connection con = DriverManager.getConnection(
"jdbc:mysql://localhost:3306/college", "root", "pass");
// 3. STATEMENT (SQL carrier!)
Statement st = con.createStatement();
// 4. RESULT (rows!)
ResultSet rs = st.executeQuery("SELECT id, name FROM student");
while (rs.next()) { // row by row!
System.out.println(rs.getInt("id") + " " + rs.getString("name"));
}
// 5. CLOSE (reverse! rs → st → con!)
rs.close(); st.close(); con.close();
}
}
3. URL Anatomy
jdbc:mysql://localhost:3306/college = api:db://host:port/db! Oracle/Postgres differ only here!
4. Traps
- No jar on classpath →
ClassNotFoundException/No suitable driver(add mysql-connector jar!). Class.forNameoptional (Java 6+ auto!) but exams still ask!- Close in reverse (leak!); prefer try-with-resources (auto-close!).
5. Exam Points
- Five steps program — 7-10 marks, #1 JDBC question.
- URL parts + close order — 3-5 marks, frequent.