Unit 5 · Lesson 414 minAcademic review pending

A Java object asks a database a question

The course objective names JDBC even though the unit list does not. This short bridge shows the complete path: open a connection, send a parameterized query, read rows, and close every resource safely.

Choose explanation

After this lesson

You should be able to

Name the Connection, PreparedStatement, and ResultSet roles in one query.
Use try-with-resources so database resources close on success or failure.

Three objects, three jobs

A Connection represents one live conversation with a database. A PreparedStatement represents one SQL command with placeholders for values. A ResultSet is the cursor over rows returned by a SELECT. Keeping those jobs separate makes the code readable and lets the JDBC driver manage database-specific details behind standard Java interfaces.

PreparedStatement is also the safe way to supply values. The SQL structure stays fixed while setInt or setString supplies data separately, so a student's input cannot become part of the SQL grammar. Do not build queries by joining raw input into a String.

One parameterized JDBC query

String sql = "SELECT name FROM student WHERE roll_no = ?";

try (Connection connection = dataSource.getConnection();
     PreparedStatement statement = connection.prepareStatement(sql)) {
    statement.setInt(1, rollNumber);

    try (ResultSet rows = statement.executeQuery()) {
        while (rows.next()) {
            System.out.println(rows.getString("name"));
        }
    }
}

Make the idea stick

Now try it yourself

java-labcheckpoint

ORDER

Run one safe database query

Order the JDBC resource flow from connection to cleanup.

Tap the next correct stepProgress: 0/5

Build the order one step at a time.

The compiler cannot provide a database

The external Java compiler can check JDBC syntax only if the required driver and database are available, which a simple online compiler normally does not provide. For this pilot, reason about the resource flow here; a later database lab can supply an isolated database and test data. The course must never embed real database passwords in a lesson or browser bundle.

Try it yourself

Modify the query to fetch name and marks for one department supplied as text.

Need a hint?

Use WHERE department = ? and setString(1, department). Keep the value out of the SQL String.

Check the worked solution

The placeholder preserves a fixed query structure while setString supplies the department as data.

String sql = "SELECT name, marks FROM student WHERE department = ?";
try (PreparedStatement statement = connection.prepareStatement(sql)) {
    statement.setString(1, department);
    try (ResultSet rows = statement.executeQuery()) {
        while (rows.next()) {
            System.out.println(rows.getString("name") + " " + rows.getInt("marks"));
        }
    }
}

Quick check

Why is PreparedStatement preferred when a query contains student-supplied text?

Select an answer to check your thinking.

Why this lesson exists

Syllabus mapping

Course Objective 4: To Develop data-centric applications using JDBC. · Outcome bridge — JDBC is named in the official objective but omitted from the unit topic list.

Maps to course outcome CO1.