Name Section. CS 21a Introduction to Computing I 1 st Semester Final Exam

Transcription

1 CS a Introduction to Computing I st Semester Final Exam Write your name on each sheet. I. Multiple Choice. Encircle the letter of the best answer. ( points each) Answer questions and based on the following program: 0 public class MyApplet extends JApplet private JLabel mylabel; int age; public void init() Container c = this.getcontentpane(); c.setlayout( new FlowLayout() ); mylabel = new JLabel(); c.add( this.mylabel ); age = JOptionPane.showInputDialog( "Enter your age: "); mylabel.settext( "You are " + age + " years old.");. The above program should begin which of the following? a. import javax.swing.*; import java.awt.*; import java.awt.event.*; b. nothing; it s fine as it is c. import java.io.*; d. import javax.swing.*; import java.awt.*;. Which line will produce a compile-time error, assuming the necessary import lines have been added? a. b. c. d. Answer questions to based on the following program and its associated html file: import javax.swing.*; import java.awt.*; import java.awt.event.*; public class MultipleChoice extends JApplet implements ActionListener

2 private Panel question; private JTextArea questionarea; private Panel choicespanel; private JButton A, B, C, D; private JLabel labela, labelb, labelc, labeld; private Panel feedback; private JTextArea feedbackarea; public void init() Container c = this.getcontentpane(); c.setlayout( new BorderLayout() ); c.setbackground( Color.blue ); question = new Panel(); question.setlayout( new BorderLayout()); questionarea = new JTextArea(, 0); questionarea.settext( "0 + 0" ); question.add( "Center", questionarea ); question.add( "North", new JLabel( "Question:" ) ); choicespanel = new Panel(); choicespanel.setlayout( new GridLayout(,) ); A = new JButton( "A" ); B = new JButton( "B" ); C = new JButton( "C" ); D = new JButton( "D" ); labela = new JLabel( " 0" ); labelb = new JLabel( " 0" ); labelc = new JLabel( " 00" ); labeld = new JLabel( " 0" ); choicespanel.add( A ); choicespanel.add( labela ); choicespanel.add( new JLabel(" ") ); choicespanel.add( B ); choicespanel.add( labelb ); choicespanel.add( new JLabel(" ") ); choicespanel.add( C ); choicespanel.add( labelc ); choicespanel.add( new JLabel(" ") ); choicespanel.add( D ); choicespanel.add( labeld ); choicespanel.add( new JLabel(" ") ); A.addActionListener(this); B.addActionListener(this); C.addActionListener(this); D.addActionListener(this); feedback = new Panel(); feedback.setlayout( new BorderLayout()); feedback.add( "North", new JLabel( "Evaluation:" )); feedbackarea = new JTextArea(, 0 ); feedback.add( "Center", feedbackarea );

3 c.add( "North", question ); c.add( "Center", choicespanel ); c.add( "South", feedback ); public void actionperformed( ActionEvent ae ) Object temp; temp = ae.getsource(); if ( temp == A ) feedbackarea.settext( "Wrong answer!" ); else if ( temp == B ) feedbackarea.settext( "That's right!" ); else if ( temp == C ) feedbackarea.settext( "Sorry!" ); else if ( temp == D ) feedbackarea.settext( "Try again!" ); <APPLET CODE=MultipleChoice.class WIDTH=00 HEIGHT=00> </APPLET>. How does the applet look onscreen? a.

4 b. c.

5 d.. What are the dimensions of the applet? a. 00 pixels in height, 00 pixels in width b. 00 pixels in height, 00 pixels in width c. lines in height, 0 spaces in width d. 00 lines in height, 00 spaces in width. What are the contents of feedbackarea when the user clicks on 0? a. That s right! b. feedbackarea s contents do not change c. Wrong answer! d. Try again!. What elements are in the West portion of container c? a. A and C b. A, C, and Evaluation c. Question, questionarea, A, C, Evaluation, and feedbackarea d. none of the above. How many JLabels are there in container c? a. b. c. d. 0. Which of the following statements is TRUE? a. questionarea and feedbackarea are the same size b. questionarea is larger than feedbackarea c. feedbackarea is larger than questionarea d. the values of questionarea and feedbackarea cannot be changed

6 Answer questions to based on the code below: import javax.swing.*; import java.awt.*; import java.awt.event.*; public class DemoAppletNested extends JApplet implements ActionListener JTextField field; JTextArea area; JButton door; JButton door; public void init() field = new JTextField( 0 ); area = new JTextArea(, 0 ); door = new JButton( "Door " ); door = new JButton( "Door " ); JPanel door = new JPanel(); Container c = this.getcontentpane(); c.setlayout( new BorderLayout() ); c.add( new JLabel( "Type data in Text Field" ), "North" ); c.add( field, "South" ); c.add( door, "West" ); c.add( door, "East" ); door.setlayout( new FlowLayout() ); door.add( new JLabel( "Results" ) ); door.add( area ); c.add( door, "Center" ); door.addactionlistener( this ); door.addactionlistener( this ); public void actionperformed( ActionEvent ae ) Object temp; temp = ae.getsource(); if ( temp == door ) String s = field.gettext(); area.settext( s + "\n" + s ); else if ( temp == door ) String s = field.gettext(); int dollars = Integer.parseInt(s); int pesos = dollars*; area.settext( "Peso Conversion:" + pesos );

7 . What is the layout of the East region of container c? a. GridLayout b. FlowLayout c. BorderLayout d. None of the above 0. Where is the field located? a. Center region of c b. door panel c. South region of c d. actionlistener. If the user types 0 into the field and then clicks the Door button, what will appear in the area? a. 0 b. 0 0 c. Peso conversion: 0 Peso conversion: 0 d. Peso conversion: 0. Which of the following is TRUE about door and door a. They have the same height as the center region of c b. They have the same height as area c. They have the same width as door d. The have the same height as c. This screenshot illustrates which of the following? a. FlowLayout b. GridBagLayout c. BorderLayout d. CardLayout

8 . The screenshot illustrates which of the following? a. FlowLayout b. TabbedPane c. BoxLayout d. CardLayout. This screenshot illustrates which of the following? a. FlowLayout b. TabbedPane c. GridLayout d. BorderLayout

9 Answer questions to based on the following code: public class MyReader ArrayList<String> a; BufferedReader buf; public MyReader() a = new ArrayList<String>(); try buf = new BufferedReader( new FileReader( source.txt ) ); catch( Exception e) m.perform(); public void perform() try for( int i = 0; i < 00; i++ ) a[ i ] = s; catch( Exception e ) public static void main( String args[] ) MyReader m = new MyReader();. The above program should begin which of the following? a. import javax.swing.*; import java.awt.*; b. import javax.io.*; import java.awt.*; c. import java.util.*; d. import javax.util.*; import java.io.*;

10 . There is a line in the code that is incorrect. Which line is this? a. b. c. d.. The incorrect line should be replaced by which of the following statements? a. String s = buf.readfile(); b. buf = new BufferedReader( new Reader( source.txt ) ); c. a.add( s ); d. a.set(s);. If the textfile named source.txt does not exist, what will happen? a. A FileNotFoundException will be thrown and then the program will stop from its execution b. A FileNotFoundException will be thrown and the exception will be caught c. An ArrayIndexOutOfBounds exception will be thrown d. A NullPointerException will be thrown Assuming that the following code fragment works, answer questions 0, and.... ArrayList<String> a = new ArrayList<String>(); String s = "Hello"; String u = "Good Morning"; 0 String v = "Good Bye"; a.add( u ); a.add( v ); a.add( s ); for( int i = ; i > 0; i-- ) String temp = a.get( i ); System.out.print( temp + ); What will be printed out? a. Hello Good Morning b. Good Morning Goodbye Hello c. Hello Goodbye Good Morning d. Hello Goodbye 0

11 . Why is the integer i in line.not initialized to even if there are strings in the program? a. Initializing integer i to will cause a NullPointerException b. Initializing integer i to will cause an ArrayIndex OutOfBoundsException c. Not initializing i to will increase the speed of the iterations d. None of the above. One line in the code fragment should be replaced so that all strings will be displayed. This line should be replaced with which of the following statements? a. for( int i = ; i > 0; i++ ) b. for( int i = ; i >= 0; i++ ) c. for( int i > ; i > 0; i++ ) d. for( int i = ; i > 0; i++ ) Answer questions to based on the following code: public class Sample int[][] myarray; public Sample() myarray = new int[][]; populategrid(); hoparound(); public void populategrid() int element = ; for( int x = 0; x < ; x++ ) for( int y = 0; y < ; y++ ) myarray[ x ][ y ] = element; element = element*; public void hoparound() int q = ; for( int x = 0; x < ; x++ ) System.out.print( myarray[ x ][ q ] + " " );

12 0 0 if( q == 0 ) q = ; else q = 0; public static void main( String args[] ) Sample s = new Sample();. When this program is executed, what will be printed out? a. 0 b. 0 0 c. 0 d.. What will be the output if line was changed to int q = 0? a. b. 0 0 c. 0 d.. What will be the output of line was changed to int q =? a. ArrayIndexOutOfBoundsException b. NullPointerException c. IOException d. EOFException. What line should be modified to increase the number of columns? a. Line b. Line c. Line d. Line. Which lines should be replaced if you wanted to implement the exact code above with arraylists instead of arrays? a.,,, b.,,, c.,,, d.,,,. Line should be replaced with what line to use a one-dimensional arraylists? a. int myarraylist(); b. String myarraylist(); c. ArrayList<String> myarraylist(); d. ArrayList<int> myarraylist();

13 Answer numbers and 0 based on the code below: public class MultipleObjects Food[] f; public MultipleObjects() f = new Food[ ]; loadfood(); loadfood(); loadfood(); public void loadfood() Burger b = new Burger(); f[ 0 ]( b ); public void loadfood() Burger b = new Burger(); f[ ] = b; public void loadfood() Softdrink s = new Burger(); f[ ] = b; public static void main( String args[] ) MultipleObject m = new MultipleObjects(); public class Burger extends Food public Burger() System.out.println( "The burger lives!" );

14 public class Softdrink public Softdrink() System.out.println( "The burger lives!" ); 0 public class Food double price; public Food() public void setprice( double price ) this.price = price;. MultipleObjects.java has erroneous lines of code. Which of the following cause the errors? a. The constructor MultipleObjects.java b. The loadfood() method c. The loadfood() method d. The loadfood() method 0. Which methods and attributes of Food will the Softdrink object inherit? a. Softdrink object will not inherit anything b. Softdrink object will inherit the price attribute only c. Softdrink object will inherit the price attribute and setprice() method d. Softdrink object will inherit the setprice() method only

15 Answer questions to based on the following code: public class Animal private String name; public Animal() name = "Nameless"; public Animal( String s ) name = s; public String getname() return name; public void makesound() System.out.println( "ZZZ.." ); public class Dog extends Animal private int numbarks; public Dog( int n ) numbarks = n; public Dog( String n ) super( n ); numbarks = ; public void makesound() for( int i = 0; i < numbarks; i++ ) System.out.println( "" ); public class Cat extends Animal public Cat( String s ) super( s ); // # public void scratch() System.out.println( "Scratch" );

16 . Which of the following methods is overridden by a subclass? a. getname() b. makesound() c. scratch() d. super(). Suppose Cat c = new Cat( Felix );, what output will result from the statement c.makesound(); a. ZZZ b. c. d. Scratch. Suppose Animal d = new Dog( Spot );, what output will result from the statement d.makesound(); a. ZZZ b. c. d. Scratch. Suppose Dog d = new Dog( );, what output will result from the statements System.out.println( d.getname() ); d.makesound(); a. b. c. Nameless d. Nameless. If the call to super( s ); in the Cat class is removed, a. The code will not compile successfully b. All Cat objects will be have the name Nameless c. There will be no superclass constructor invoked d. None of the above

17 For numbers -, consider the folowing snippet of code: 0 public void readfile() try /* [#] code to print out contents of * "classlist.txt" to "classlist-copy.txt" */ catch( FileNotFoundException fnfe ) fnfe.printstacktrace(); catch( [#] ex ) ex.printstacktrace();. To print out the contents of the file "classlist.txt" to another file called "classlist-copy.txt", which of the following lines can be used? i. BufferedReader reader = new BufferedReader( new InputStreamReader( "classlist.txt" ) ); ii. BufferedReader reader = new BufferedReader( new FileReader( "classlist.txt" ) ); iii. PrintStream printer = new PrintStream( new FileOutputStream( "classlist.txt" ) ); iv. PrintStream printer = new PrintStream( new BufferedWriter( "classlist-copy.txt" ) ); a. i and iii b. ii and iii c. ii and iv d. None of the above. If "classlist.txt" is deleted from the computer and the application is run, which code is executed? a. fnfe.printstacktrace() b. ex.printstacktrace() c. Both a and b: the code will throw two exceptions d. None of the above: the code will not throw any exceptions

18 . If the programmer chooses not to catch exceptions, he/she must a. Use FileInputStream and FileOutputStream, classes which do not throw exceptions b. Call reader.close() and printer.close() to make sure exceptions are closed c. Declare that exceptions will be thrown by the method d. Compile the program using the "javap" command to solve the problem. To catch all other exceptions related to files, line must catch a. BufferedIOException b. FileException c. EOFException d. IOException 0. In order to use a Canvas, a class must a. Extend Canvas and override the paint() method b. Extend Canvas and override the draw() method c. Execute this = Canvas.getCanvas() to assign the class to a Canvas d. Execute Graphics g = new Graphics() to draw using "g" For the numbers -, consider the following snippet of code: 0 0 int a, b; public void draw( Graphics g ) int result = a * b % ; Color mycolor; switch( result ) case 0: mycolor = Color.YELLOW; case : mycolor = Color.BLUE; case : mycolor = Color.RED; default: mycolor = Color.BLACK; g.setcolor( mycolor ); g.fillrect( 0, 0, 0, 0 );. If a = and b =, calling this method would draw a a. Filled yellow rectangle b. Filled blue rectangle c. Filled red rectangle d. Filled black rectangle

19 . If a = and b =, calling this method would draw a a. Filled yellow rectangle b. Filled blue rectangle c. Filled red rectangle d. Filled black rectangle. To draw a hollow circle instead, line must be changed to a. g.fillrect( 0, 0, 0, 0, false ); b. g.drawcircle( 0, 0, 0, 0 ); c. g.drawoval( 0, 0, 0, 0 ); d. g.fillcircle( 0, 0, 0, 0, false );. Which of the following is NOT a benefit of encapsulating shapes? a. It is easier to display similar shapes in the canvas b. Shapes can override each other c. The code is shorter and more organized d. Can use arrays or ArrayLists and inheritance to maintain the different shape objects. Which of the following is true? a. A stream is a sequence of bytes and/or characters b. Applets can read and write to text files c. An uncaught exception will always result in a compile error d. If you want to update the file without closing it yet, you can call the update() method II. True or False ( point each). Static fields are shared by all instances of the same class.. The parameter of the main method of a Java application is an array.. All exceptions thrown in a Java program have to be caught.. Arrays are objects.. flush() is a method of the PrintStream class.. setlayout() is a method of the Container class.. addactionlistener() is a method of the ActionEvent class.. JApplet is a subclass of JFrame.. Subclass variables can refer to objects of its superclass. 0. All private methods of a class can be accessed from its subclasses.