This document contains 30 multiple choice questions about Java programming concepts such as classes, objects, arrays, inheritance, interfaces, events and GUI components. It also includes code snippets and questions asking to write short code examples to demonstrate understanding of concepts like layout managers, event handling and calculations.

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1: The .class extension on a file means that the file
a.contains Java source code.
b.contains HTML.
c.is produced by the Java compiler (javac).
d.contains a machine specific executable image.
2: Which command compiles the Java source code file Welcome.java?
a.cd Welcome.java
b.javac Welcome.java
c.java Welcome.java
d.compile Welcome.java
3: A(n) ________ enables a program to read data from the user.
a.printf
b.import declaration
c.Scanner
d.main routine
4: Which of the following is a Scanner method?
a.nextLine
b.nextText
c.nextWord
d.readNext
5: Every Java application is required to have
a. at least one public static method.
b.at least one data member.
c. a String variable which holds the name of the application.
d.a content pane and several GUI components.
6: Which of the following statements about creating arrays and
initializing their elements is false?
a. The new keyword should be used to create an array.
b. When an array is created, the number of elements must be placed in
square brackets following the type of element being stored.

2. c. The elements of an array have unknown values just after the array has
been created.
d. A for loop is an excellent way to initialize the elements of an array.
7: Assume the following class declaration.
class MyClass
{
int a;
String q;
public void firstMethod()
{
int b, ;
* 7;
+ c * a;
}
}
Mark the following statements as TRUE or FALSE.
q is a reference variable which refers to the empty string. __TRUE___ b
and c are local variables. ___TRUE____ a, b, and c are primitive data
types. ___FALSE____ MyClass is a Java application. ___FALSE____
8: Which statement below could be used to randomly select a state from
an array which contains exactly 50 strings which are the names of the
states?
1 + ( int ) ( Math.random( ) * 49 ); ( int ) ( Math.random( ) * 51 ); ( int )
( Math.random( ) * 50 ); 1 + ( int ) ( Math.random( ) * 50 );
9: To draw a single line from (0, 15) to (20, 25), call the method
_________ of the Graphics class in the paintComponent method.
a.drawLine( 0, 15, 20, 25 );
b.drawString( "single line", 0, 15 );
c.drawLine( 0, 15, 20, 10 );
d.drawLine( 15, 0, 25, 20 );
10: In the Java graphics system, coordinate units are measured in
________.
a.dots
b.pixels
c.points
d.inches
11: Which is a correct way to invoke the static method sqrt of the Math
class?
a.sqrt( 900 );.
b.math.sqrt( 900 );.
c.Math.sqrt( 900 );.
d.Math Math(); math.sqrt( 900 );.
12: When an object is concatenated with a String
a.a compilation error occurs.

3. b.a runtime error occurs.
c.the object’s toString method is implicitly called to obtain the String
representation of the object.
d.the object’s class name is used.
13: What do the following statements do?
double array[];
double[ 14 ];
a. Creates a double array containing 13 elements.
b.Creates a double array containing 14 elements.
c. Creates a double array containing 15 elements.
d. Declares but does not create a double array.
14: Consider the class below:
public class Test
{
public static void main( String args[] )
{
int a[];
int[ 10 ];
for ( int ; i <a.length; i++ )
a[ i ] = i + 1 * 2;
int ;
for ( int ; i <a.length; i++ )
result += a[ i ];
System.out.printf( "Result is: %dn", result );
} // end main
} // end class Test
The output of this Java program will be
a. Result is: 62
b. Result is: 64
c. Result is: 65
d. Result is: 67
15: Which method call converts the value in variable stringVariable to
an integer?
a. Convert.toInt( stringVariable )
b. Convert.parseInt( stringVariable )
c. Integer.parseInt( stringVariable )
d.Integer.toInt( stringVariable )
16: Which of the following is the method used to display a dialog box to
gather input?
a. showMessageDialog
b. getInput

4. c. inputDialog
d. showInputDialog
17: provides the basic attributes and behaviors of a window—a title bar
at the top of the window, and buttons to minimize, maximize and close the
window.
a. JLabel
b. JFrame
c. JSwing
d. JWindowControl
18: Which of the following does not generate an event?
a. Typing in a text field.
b. Clicking on a button.
c. Viewing the text in a label.
d. Moving the mouse.
19: When the user presses Enter in a JTextField, the GUI component
generates an , which is processed by an object that implements the
interface .
a. ActionEvent, ActionListener
b. ActionEvent, ActionEventListener
c. TextEvent, TextListener
d. TextEvent, TextEventListener
202: When the user clicks a JCheckBox, a(n) occurs.
a. CheckedEvent
b. ButtonEvent
c. ItemEvent
d. ActionEvent
21: Which method determines if a JRadioButton is selected?
a. isSelected
b. getSelected
c. selected
d. none of the above
22: The logical relationship between radio buttons is maintained by
objects of what class?
a. MutualExclusionGroup
b. RadioButtonGroup
c. Group
d. ButtonGroup
23: Which layout manager is the default for JPanel?
a. FlowLayout
b. BorderLayout
c. GridLayout
d. none of the above
24. A Java interface
a. must contain only public abstract methods.

5. b. can be implemented by any number of Java classes.
c. reference can refer to objects of any class which implements the
interface.
d. all of the above
25. Writing an application which handles mouse events can be done by
a. having a GUI class implement the KeyListener interface.
b. creating an inner class which extends the MouseAdapter class.
c. adding mouse functionality to the paintComponent method.
d. all of the above
26. Write a Java statement using printf to output the value of Math.PI,
showing 5 digits after the decimal point.
27. Write a Java statement that declares a class called MyDrawingPanel
that inherits from the JPanel class. Do not declare any methods or
member variables in this class.
28. Class Cap has been defined as a base class, and class BaseballCap
inherits from class Cap. Is the following Java statement legal? Explain
why or why not.
29. Write a few lines of code that would place 2 radio buttons labeled on
and off side by side into the top part of a JFrame based window. Assume
that the code you are writing is inside the constructor of an application
which inherits from JFrame. Declare any variables that you need. You
should only need 6-8 lines of code.
30. This Java application is supposed to do the following. There are 2
text fields for user input. The first is used to input a voltage value. The
second is used to input a resistance value in ohms. All values are floating
point values. The user clicks a button to perform a calculation. One
button causes the program to calculate and display the current flowing
through the resistor, / R. Another button causes the program to calculate
the power being dissipated by the resistor, * V. The result of the selected
calculation is displayed in a single output text area. The output string
should say something like this: “10 volts dropped across 1000 ohms
creates 0.1 amps.” Clicking of a button generates the event which causes
the program to do the selected calculation and update the output area.
The user interface has already been setup in the class that follows. Your
job is to implement the ButtonHandler nested inner class which handles
button events, does the requested calculation and displays the
appropriate result.

6. b. can be implemented by any number of Java classes.
c. reference can refer to objects of any class which implements the
interface.
d. all of the above
25. Writing an application which handles mouse events can be done by
a. having a GUI class implement the KeyListener interface.
b. creating an inner class which extends the MouseAdapter class.
c. adding mouse functionality to the paintComponent method.
d. all of the above
26. Write a Java statement using printf to output the value of Math.PI,
showing 5 digits after the decimal point.
27. Write a Java statement that declares a class called MyDrawingPanel
that inherits from the JPanel class. Do not declare any methods or
member variables in this class.
28. Class Cap has been defined as a base class, and class BaseballCap
inherits from class Cap. Is the following Java statement legal? Explain
why or why not.
29. Write a few lines of code that would place 2 radio buttons labeled on
and off side by side into the top part of a JFrame based window. Assume
that the code you are writing is inside the constructor of an application
which inherits from JFrame. Declare any variables that you need. You
should only need 6-8 lines of code.
30. This Java application is supposed to do the following. There are 2
text fields for user input. The first is used to input a voltage value. The
second is used to input a resistance value in ohms. All values are floating
point values. The user clicks a button to perform a calculation. One
button causes the program to calculate and display the current flowing
through the resistor, / R. Another button causes the program to calculate
the power being dissipated by the resistor, * V. The result of the selected
calculation is displayed in a single output text area. The output string
should say something like this: “10 volts dropped across 1000 ohms
creates 0.1 amps.” Clicking of a button generates the event which causes
the program to do the selected calculation and update the output area.
The user interface has already been setup in the class that follows. Your
job is to implement the ButtonHandler nested inner class which handles
button events, does the requested calculation and displays the
appropriate result.