Part 1
1. Which of the following is a correct interface?
abstract interface A { abstract void print({ };}
interface A { void print() { }; }
abstract interface A { print(); }
interface A { void print();}
2. Analyze the following code.
import java.util.*; // 1
public class Test { // 2
public static void main(String[ ] args) { // 3
Calendar[ ] calendars = new Calendar[10]; // 4
calendars[0] = new Calendar(); // 5
calendars[1] = new GregorianCalendar(); // 6
} // 7
} // 8
The program has a compile error on Line 4 because java.util.Calendar is an abstract class.
The program has no compile errors.
The program has a compile error on Line 6 because Calendar[1] is not of a GregorianCalendar type.
The program has a compile error on Line 5 because java.util.Calendar is an abstract class.
3. What is the output of Integer.parseInt("10", 2)?
Invalid statement;
2;
1;
10;
4. Analyze the following code.
Number numberRef = new Integer(0);
Double doubleRef = (Double)numberRef;
The compiler detects that numberRef is not an instance of Double.
The program runs fine, since Integer is a subclass of Double.
A runtime class casting exception occurs, since numberRef is not an instance of Double.
You can convert an int to double, so you can cast an Integer instance to a Double instance.
There is no such class named Integer. You should use the class Int.
5. To divide BigDecimal b1 by b2, and assign the result to b1, you write _____.
b1 = b1.divide(b2);.
b1 = b2.divide(b1);.
b1 = b2.divide(b1);.
b1.divide(b2);.
b2.divide(b1);.
6. Analyze the following code.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Test extends JFrame {
public void Test() {
JButton jbtOK = new JButton("OK");
add(jbtOK);
jbtOK.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
System.out.println("The OK button is clicked");
}
});
}
public static void main(String[ ] args) {
JFrame frame = new Test();
frame.setSize(300, 300);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}
The actionPerformed method is not executed when you click the OK button, because no instance of Test is registered with jbtOK.
When you run the program, the button is not displayed, because the constructor is declared wrong. It should be declared public Test(), not public void Test().
The message, "The OK button is clicked," is displayed when you click the OK button.
The program has a compile error because no listeners are registered with jbtOK.
The program has a runtime error because no listeners are registered with jbtOK.
7. To listen to mouse-clicked events, the listener must implement the _____ interface or extend the _____ adapter.
MouseMotionListener/MouseMotionAdapter
WindowListener/WindowAdapter
ComponentListener/ComponentAdapter
MouseListener/MouseAdapter
8. Clicking the closing button on the upper-right corner of a frame generates a(n) _____ event.
ContainerEvent
WindowEvent
MouseMotionEvent
ItemEvent
ComponentEvent
9. Which statement is true about a non-static inner class?
It must implement an interface.
It must be final if it is declared in a method scope.
It is accessible from any other class.
It can access private instance variables in the enclosing object.
It can only be instantiated in the enclosing class.
10. The method in the ActionEvent _____ returns the action command of the button.
getActionCommand()
getModifiers()
getID()
paramString()
Part 2
1. Which of the following statements are false?
If you compile an interface without errors, but with warnings, a .class file is created for the interface.
If you compile an interface without errors, a .class file is created for the interface.
If you compile a class with errors, a .class file is created for the class.
If you compile a class without errors but with warnings, a .class file is created.
2. To divide BigDecimal b1 by b2, and assign the result to b1, you write _____.
b1 = b1.divide(b2);.
b1 = b2.divide(b1);.
b1 = b2.divide(b1);.
b1.divide(b2);.
b2.divide(b1);.
3. In JDK 1.5, you may directly assign a primitive data type value to a wrapper object. This is called _____.
auto boxing.
auto unboxing.
auto casting.
auto conversion.
4. Assume Calendar calendar = new GregorianCalendar(). _____ returns the month of the year.
calendar.get(Calendar.MONTH)
calendar.get(Calendar.WEEK_OF_MONTH)
calendar.get(Calendar.MONTH_OF_YEAR)
calendar.get(Calendar.WEEK_OF_YEAR)
5. What is the output of the following code?
public class Test {
public static void main(String[ ] args) {
java.math.BigInteger x = new java.math.BigInteger("3");
java.math.BigInteger y = new java.math.BigInteger("7");
x.add(y);
System.out.println(x);
}
}
3
11
10
4
6. The interface _____ should be implemented to listen for a button action event.
FocusListener
ContainerListener
ActionListener
MouseListener
WindowListener
7. Which of the following is not a correct name for listener adapters?
MouseAdapter
ActionAdapter
KeyAdapter
WindowAdapter
8. Analyze the following code.
import java.awt.*; // 1
import java.awt.event.*; // 2
import javax.swing.*; // 3
// 4
public class Test extends JFrame { // 5
public Test() { // 6
JButton jbtOK = new JButton("OK"); // 7
JButton jbtCancel = new JButton("Cancel"); // 8
getContentPane().add(jbtOK); // 9
getContentPane().add(jbtCancel); // 10
jbtOK.addActionListener(this); // 11
jbtCancel.addActionListener(this); // 12
} // 13
// 14
public void actionperformed(ActionEvent e) { // 15
System.out.println("A button is clicked"); // 16
} // 17
// 18
public static void main(String[ ] args) { // 19
JFrame frame = new Test(); // 20
frame.setSize(300, 300); // 21
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // 22
frame.setVisible(true); // 23
} // 24
} // 25 (Points : 3)
The program has runtime errors on Lines 9 and 10 because jbtOK and jbtCancel are added to the same location in the container.
The program has compile errors on Line 15 because the signature of actionperformed is wrong.
The program has compile errors on Line 20 because new Test() is assigned to frame (a variable of JFrame).
The program has compile errors on Lines 11 and 12 because Test does not implement ActionListener.
9. Pressing a button generates a(n) _____ event.
ContainerEvent
MouseMotionEvent
ItemEvent
ActionEvent
MouseEvent
10. The method in the ActionEvent _____ returns the action command of the button.
getActionCommand()
getModifiers()
getID()
paramString().