7: Assume the following class declaration.
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  • 1. TO Buy the Tutorial Visit Our Website Select the best answer. 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.