Core Java Assessment

Given that you are working with a JDBC 4.0 driver, which three are required for this JDBC driver to be compliant?

• Must include a META-INF/services/java.sql.Driver file

• Must provide implementations of Driver, Connection, Statement, and ResultSet interfaces

• Must support scrollable ResultSets

• Must support PreparedStatement and CallableStatement

• Must support transactions

Which three are available through an instance of DatabaseMetaData?

• The number of rows returned

• The name of the JDBC driver

• The default transaction isolation level

• The last query used

• The names of stored procedures in the database

Given this code fragment:

Statement stmt = conn.createStatement();

ResultSet rs;

String query = "<QUERY HERE>";

stmt.execute(query);

if ((rs = stmt.getResultSet()) != null) {

System.out.println("Results");

}

if (stmt.getUpdateCount() > -1) {

System.out.println("Update");

}

Which query statements entered into <QUERY HERE> produce the output that follows the query string (in the following answer), assuming each query is valid? (Choose all that apply.)

• "SELECT * FROM Customer"

  Results

• . "INSERT INTO Book VALUES ('1023456789', 'One Night in Paris', '1984-10-20',

  'Hardcover', 13.95)"

  Update

• "UPDATE Customer SET Phone = '555-234-1021' WHERE CustomerID = 101"

  Update

• "SELECT Author.LastName FROM Author"

  Results

• . "DELETE FROM Book WHERE ISBN = '1023456789'"

  Update

Given:

String call = "{CALL REMOVEBOOKS(?, ?)}";

String titleToRemove = null;

int maxBooks = 0;

CallableStatement cstmt = conn.prepareCall(call);

String titles = "%Hero%";

int numBooksRemoved;

// Code added here

If REMOVEBOOKS is a stored procedure that takes an INOUT integer parameter as its first argument and an IN String parameter as its second argument, which code blocks, when placed at the line

// Code added here, could correctly execute the stored procedure and return a result?

• cstmt.setInt(0, maxBooks);

  cstmt.setString(1, titleToRemove);

  cstmt.registerOutParameter(0, java.sql.Types.INTEGER);

  cstmt.execute();

  numBooksRemoved = cstmt.getInt(0);

• cstmt.setInt(1, maxBooks);

  cstmt.setString(2, titleToRemove);

  cstmt.registerOutParameter(1, java.sql.Types.INTEGER);

  cstmt.executeQuery(query);

  numBooksRemoved = cstmt.getInt(1);

• cstmt.setInt(1, maxBooks);

  cstmt.setString(2, titleToRemove);

  cstmt.execute();

  cstmt.registerOutParameter(1, java.sql.Types.INTEGER);

  numBooksRemoved = cstmt.getInt(1);

• cstmt.setInt(1, maxBooks);

  cstmt.setString(2, titleToRemove);

  cstmt.registerOutParameter(1, java.sql.Types.INTEGER);

  ResultSet rs = cstmt.executeQuery();

  rs.next();

  numbBooks = rs.getInt(1);

• cstmt.setInt(1, maxBooks);

  cstmt.setString(2, titleToRemove);

  cstmt.registerOutParameter(1, java.sql.Types.INTEGER);

  cstmt.execute();

  numBooksRemoved = cstmt.getInt(1);

Assume you have a class that holds two private variables: a and b. Which of the following pairs can prevent concurrent access problems in that class? (Choose all that apply.)

• public synchronized int read(){return a+b;}

  public synchronized void set(int a, int b){this.a=a;this.b=b;}

• public int read(){synchronized(a){return a+b;}}

  public void set(int a, int b){synchronized(a){this.a=a;this.b=b;}}

• public int read(){synchronized(a){return a+b;}}

  public void set(int a, int b){synchronized(b){this.a=a;this.b=b;}}

• public synchronized(this) int read(){return a+b;}

  public synchronized(this) void set(int a, int b){this.a=a;this.b=b;}

• public int read(){synchronized(this){return a+b;}}

  public void set(int a, int b){synchronized(this){this.a=a;this.b=b;}}

public class TwoThreads {

static Thread laurel, hardy;

public static void main(String[] args) {

laurel = new Thread() {

public void run() {

System.out.println("A");

try {

hardy.sleep(1000);

} catch (Exception e) {

System.out.println("B");

}

System.out.println("C");

}

};

hardy = new Thread() {

public void run() {

System.out.println("D");

try {

laurel.wait();

} catch (Exception e) {

System.out.println("E");

}

System.out.println("F");

}

};

laurel.start();

hardy.start();

}

}

Which letters will eventually appear somewhere in the output? (Choose all that apply.)

• A

• C

• D

• E

• F

This class is intended to allow users to write a series of messages so that

each message is identified with a timestamp and the name of the thread that wrote the message:

public class Logger {

private StringBuilder contents = new StringBuilder();

public void log(String message) {

contents.append(System.currentTimeMillis());

contents.append(": ");

contents.append(Thread.currentThread().getName());

contents.append(message);

contents.append("\n");

}

public String getContents() { return contents.toString(); }

}

How can we ensure that instances of this class can be safely used by multiple threads?

• This class is already thread-safe

• Replacing StringBuilder with StringBuffer will make this class thread-safe

• Synchronize the log() method only

• Synchronize the getContents() method only

• Synchronize both log() and getContents()

Given:

public class TestObj {

public static void main(String[] args) {

Object o = new Object() {

public boolean equals(Object obj) {

return true;

}

}

System.out.println(o.equals("Fred"));

}

}

What is the result?

• An exception occurs at runtime

• Compilation fails because of an error on line 3

• Compilation fails because of an error on line 4

• Compilation fails because of an error on line 8

• Compilation fails because of an error on a line other than 3, 4, or 8

Given:

public class Car {

class Engine {

// insert code here

}

public static void main(String[] args) {

new Car().go();

}

void go() {

new Engine();

}

void drive() { System.out.println("hi"); }

}

Which, inserted independently at line 5, produce the output "hi"? (Choose all that apply.)

• { Car.drive(); }

• { this.drive(); }

• { Car.this.drive(); }

• Engine() { this.drive(); }

• Engine() { Car.this.drive(); }

Given:

import java.util.*;

public class Pockets {

public static void main(String[] args) {

String[] sa = {"nickel", "button", "key", "lint"};

Sorter s = new Sorter();

for(String s2: sa) System.out.print(s2 + " ");

Arrays.sort(sa,s);

System.out.println();

for(String s2: sa) System.out.print(s2 + " ");

}

class Sorter implements Comparator<String> {

public int compare(String a, String b) {

return b.compareTo(a);

}

}

}

What is the result?

• Compilation fails

• button key lint nickel

  nickel lint key button

• nickel button key lint

  button key lint nickel

• nickel button key lint

  nickel lint key button

• An exception is thrown at runtime