1. Explain the difference between Statement, PreparedStatement, and CallableStatement in JDBC.

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1. Explain the difference between Statement, PreparedStatement, and CallableStatement in JDBC.

Overview

JDBC (Java Database Connectivity) is a pivotal Java API for connecting and executing operations in the database. Understanding the difference between Statement, PreparedStatement, and CallableStatement is crucial for efficiently managing database operations, ensuring data security, and optimizing performance in Java applications.

Key Concepts

  • Statement: Used for executing simple SQL queries without parameters.
  • PreparedStatement: Extends Statement, precompiles SQL queries, and allows the use of input parameters, enhancing performance and security.
  • CallableStatement: Extends PreparedStatement, used for executing stored procedures that can return results.

Common Interview Questions

Basic Level

  1. What is the difference between Statement and PreparedStatement in JDBC?
  2. How do you use a PreparedStatement to insert data into a database?

Intermediate Level

  1. Why is PreparedStatement preferred over Statement in JDBC?

Advanced Level

  1. How can you use a CallableStatement to execute a stored procedure that returns multiple results?

Detailed Answers

1. What is the difference between Statement and PreparedStatement in JDBC?

Answer:
Statement is used for executing a simple SQL query without parameters. It is compiled every time it's executed. PreparedStatement, on the other hand, represents a precompiled SQL statement that can be executed multiple times with different input parameters, improving performance and security by preventing SQL injection attacks.

Key Points:
- Statement is less efficient for repeated executions of similar SQL queries.
- PreparedStatement improves performance by reducing the time needed for query compilation.
- PreparedStatement enhances security by allowing parameterized queries.

Example:

// Using Statement
Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery("SELECT * FROM users WHERE userId = 1");

// Using PreparedStatement
PreparedStatement pstmt = conn.prepareStatement("SELECT * FROM users WHERE userId = ?");
pstmt.setInt(1, 1);
ResultSet rs = pstmt.executeQuery();

2. How do you use a PreparedStatement to insert data into a database?

Answer:
To use a PreparedStatement for inserting data, create a precompiled SQL statement with placeholders for values, set these values using appropriate setter methods (e.g., setInt, setString), and execute the statement.

Key Points:
- Use placeholders ? for parameters to prevent SQL injection.
- Call appropriate setter methods based on data type.
- Use executeUpdate() for insertion.

Example:

String query = "INSERT INTO users(name, email) VALUES(?, ?)";
PreparedStatement pstmt = conn.prepareStatement(query);
pstmt.setString(1, "John Doe");
pstmt.setString(2, "john.doe@example.com");
int affectedRows = pstmt.executeUpdate();

3. Why is PreparedStatement preferred over Statement in JDBC?

Answer:
PreparedStatement is preferred over Statement primarily for two reasons: performance optimization and security. Precompilation and reusable query plan of PreparedStatement make it faster for executing similar SQL queries multiple times. Its support for parameterized queries helps prevent SQL injection attacks, making applications more secure.

Key Points:
- Performance benefit from precompilation.
- Security enhancement through parameterization.
- Reduces parsing time as SQL statement is compiled only once.

Example:
Refer to the examples provided in questions 1 and 2 for code illustrations.

4. How can you use a CallableStatement to execute a stored procedure that returns multiple results?

Answer:
A CallableStatement is used to execute stored procedures. To handle multiple results, use methods like execute, getResultSet, and getMoreResults. After executing the CallableStatement, loop through the results using getMoreResults and getResultSet to process each.

Key Points:
- Use CallableStatement for stored procedures.
- Handle multiple results or update counts.
- Loop with getMoreResults and getResultSet.

Example:

CallableStatement cstmt = conn.prepareCall("{call GetEmployeeDetails(?)}");
cstmt.setInt(1, 1001); // Setting parameter value
boolean hasResults = cstmt.execute();
while (hasResults) {
    ResultSet rs = cstmt.getResultSet();
    while (rs.next()) {
        // Process result set
    }
    rs.close();
    hasResults = cstmt.getMoreResults(); // Check for more results
}

This guide covers the essentials of using Statement, PreparedStatement, and CallableStatement in JDBC, providing a solid foundation for interview preparation.

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