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Jb0200r: Review

Module by: R.G. (Dick) Baldwin. E-mail the author

Summary: This module contains review questions and answers keyed to the module titled Jb0200: Java OOP: Variables.

Preface

This module contains review questions and answers keyed to the module titled Jb0200: Java OOP: Variables .

The questions and the answers are connected by hyperlinks to make it easy for you to navigate from the question to the answer and back again.

Questions

Question 1 .

Write a Java application that reads characters from the keyboard until encountering the # character. Echo each character to the screen as it is read. Terminate the program when the user enters the # character.

Answer 1

Question 2

What is the common name for the Java program element that is used to contain data that changes during the execution of the program?

Answer 2

Question 3

What must you do to make a variable available for use in a Java program?

Answer 3

Question 4

True or false? In Java, you are required to initialize the value of all variables when they are declared.

Answer 4

Question 5

Show the proper syntax for declaring two variables and initializing one of them using a single Java statement.

Answer 5

Question 6

True or false? The Java compiler will accept statements with type mismatches provided that a suitable type conversion can be implemented by the compiler at compile time.

Answer 6

Question 7

Show the proper syntax for the declaration of a variable of type String[] in the argument list of the main method of a Java program and explain its purpose.

Answer 7

Question 8

Describe the purpose of the type definition in Java.

Answer 8

Question 9

True or false? Variables of type int can contain either signed or unsigned values.

Answer 9

Question 10

What is the important characteristic of type definitions in Java that strongly supports the concept of platform independence of compiled Java programs?

Answer 10

Question 11

What are the two major categories of types in Java?

Answer 11

Question 12

What is the maximum number of values that can be stored in a variable of a primitive type in Java?

Answer 12

Question 13

List the primitive types in Java.

Answer 13

Question 14

True or false? Java stores variables of type char according to the 8-bit extended ASCII table.

Answer 14

Question 15

True or false? In Java, the name of a primitive variable evaluates to the value stored in the variable.

Answer 15

Question 16

True or false? Variables of primitive data types in Java are true objects.

Answer 16

Question 17

Why do we care that variables of primitive types are not true objects?

Answer 17

Question 18

What is the name of the mechanism commonly used to convert variables of primitive types to true objects?

Answer 18

Question 19

How can you tell the difference between a primitive type and a wrapper for the primitive type when the two are spelled the same?

Answer 19

Question 20

Show the proper syntax for declaring a variable of type double and initializing its value to 5.5.

Answer 20

Question 21

Show the proper syntax for declaring a variable of type Double and initializing its value to 5.5.

Answer 21

Question 22

Show the proper syntax for extracting the value from a variable of type Double .

Answer 22

Question 23

True or false? In Java, the name of a reference variable evaluates to the address of the location in memory where the variable is stored.

Answer 23

Question 24

What is a legal identifier in Java?

Answer 24

Question 25

What are the rules for variable names in Java?

Answer 25

Question 26

What is meant by the scope of a Java variable?

Answer 26

Question 27

What are the four possible scope categories for a Java variable?

Answer 27

Question 28

What is a member variable?

Answer 28

Question 29

Where are local variables declared in Java?

Answer 29

Question 30

What is the scope of a local variable in Java?

Answer 30

Question 31

What defines a block of code in Java?

Answer 31

Question 32

What is the scope of a variable that is declared within a block of code that is defined within a method and which is a subset of the statements that make up the method?

Answer 32

Question 33

What is the scope of a variable declared within the initialization clause of a for statement in Java? Provide an example code fragment.

Answer 33

Question 34

What are method parameters and what are they used for?

Answer 34

Question 35

What is the scope of a method parameter ?

Answer 35

Question 36

What are exception handler parameters ?

Answer 36

Question 37

Write a Java application that illustrates member variables (class and instance) , local variables, and method parameters.

Answer 37

Question 38

True or false? Member variables in a Java class can be initialized when the class is defined.

Answer 38

Question 39

How are method parameters initialized in Java?

Answer 39

Listings

What is the meaning of the following two images?

This image was inserted here simply to insert some space between the questions and the answers to keep them from being visible on the screen at the same time.

The image is also an example of the kinds of things that we do in my course titled ITSE 2321, Object-Oriented Programming.

Missing image

This image was also inserted for the purpose of inserting space between the questions and the answers.

Missing image

Answers

Answer 39

Method parameters are initialized by the values passed to the method.

Back to Question 39

Answer 38

Answer 37

See the application named member1 in this module for an example of such an application.

Back to Question 37

Answer 36

Exception handler parameters are arguments to exception handlers, which will be discussed in a future module.

Back to Question 36

Answer 35

The scope of a method parameter is the entire method for which it is a parameter.

Back to Question 35

Answer 34

Method parameters are the formal arguments of a method. Method parameters are used to pass values into and out of methods.

Back to Question 34

Answer 33

Java treats the scope of a variable declared within the initialization clause of a for statement to be limited to the total extent of the for statement. A sample code fragment follows where cnt is the variable being discussed:

Note:


for(int cnt = 0; cnt < max; cnt++){
  //do something
}//end of 

Back to Question 33

Answer 32

In Java, the scope can be reduced by placing it within a block of code within the method. The scope extends from the point at which it is declared to the end of the block of code in which it is declared.

Back to Question 32

Answer 31

A block of code is defined by enclosing it within curly brackets as shown below

{ ... } .

Back to Question 31

Answer 30

The scope of a local variable extends from the point at which it is declared to the end of the block of code in which it is declared.

Back to Question 30

Answer 29

In Java, local variables are declared within the body of a method or constructor, or within a block of code contained within the body of a method or constructor.

Back to Question 29

Answer 28

A member variable is a member of a class ( class variable) or a member of an object instantiated from that class ( instance variable). It must be declared within a class, but not within the body of a method or constructor of the class.

Back to Question 28

Answer 27

The scope of a variable places it in one of the following four categories:

  • member variable
  • local variable
  • method parameter
  • exception handler parameter

Back to Question 27

Answer 26

The scope of a Java variable is the block of code within which the variable is accessible.

Back to Question 26

Answer 25

The rules for Java variable names are as follows:

  • Must be a legal Java identifier consisting of a series of Unicode characters.
  • Must not be the same as a Java keyword and must not be true or false.
  • Must not be the same as another variable whose declaration appears in the same scope.

Back to Question 25

Answer 24

In Java, a legal identifier is a sequence of Unicode letters and digits of unlimited length. The first character must be a letter. All subsequent characters must be letters or numerals from any alphabet that Unicode supports. In addition, the underscore character ( _ ) and the dollar sign ( $ ) are considered letters and may be used as any character including the first one.

Back to Question 24

Answer 23

False. The name of a reference variable evaluates to either null, or to information that can be used to access an object whose reference has been stored in the variable.

Back to Question 23

Answer 22

Later versions of Java support either syntax shown in Listing 1 .

1
Listing 1: Listing for Answer 22.

class test{
  public static void main(String[] args){
    Double var1 = 5.5;
    double var2 = var1.doubleValue();
    System.out.println(var2);

    double var3 = var1;
    System.out.println(var3);
  }//end main
}//end class test

Back to Question 22

Answer 21

The proper syntax for early versions of Java is shown below. Note the upper-case D . Also note the instantiation of a new object of type Double .

Note:


Double myWrappedData = new Double(5.5);

Later versions of Java support the following syntax with the new object of type Double being instantiated automatically:

Note:


Double myWrappedData = 5.5;

Back to Question 21

Answer 20

The proper syntax is shown below. Note the lower-case d .

Note:


double myPrimitiveData = 5.5;

Back to Question 20

Answer 19

The name of the primitive type begins with a lower-case letter and the name of the wrapper type begins with an upper-case letter such as double and Double . Note that in some cases, however, that they are not spelled the same. For example, the Integer class is the wrapper for type int .

Back to Question 19

Answer 18

Wrapper classes

Back to Question 18

Answer 17

This has some ramifications as to how variables can be used (passing to methods, returning from methods, etc.) . For example, all variables of primitive types are passed by value to methods meaning that the code in the method only has access to a copy of the variable and does not have the ability to modify the variable.

Back to Question 17

Answer 16

False. Primitive data types in Java (int, double, etc.) are not true objects.

Back to Question 16

Answer 15

Answer 14

False. The char type in Java is a 16-bit Unicode character.

Back to Question 14

Answer 13

  • byte
  • short
  • int
  • long
  • float
  • double
  • char
  • boolean

Back to Question 13

Answer 12

Primitive types contain a single value.

Back to Question 12

Answer 11

Java supports both primitive types and reference (or object) types.

Back to Question 11

Answer 10

In Java, a variable of a specified type is represented exactly the same way regardless of the platform on which the application or applet is being executed.

Back to Question 10

Answer 9

False. In Java, all variables of type int contain signed values.

Back to Question 9

Answer 8

All variables in Java must have a defined type . The definition of the type determines the set of values that can be stored in the variable and the operations that can be performed on the variable.

Back to Question 8

Answer 7

The syntax is shown in boldface below:

Note:

public static void main( String[] args )

In this case, the type of variable declared is an array of type String named args (type String[]) . The purpose of the String array variable in the argument list is to make it possible to capture arguments entered on the command line.

Back to Question 7

Answer 6

False. Fortunately, Java provides very strict type checking and generally refuses to compile statements with type mismatches.

Back to Question 6

Answer 5

Note:


int firstVariable, secondVariable = 10; 

Back to Question 5

Answer 4

False: In Java, it is possible to initialize the value of a variable when it is declared, but initialization is not required. (Note however that in some situations, the usage of the variable may require that it be purposely initialized.) .

Back to Question 4

Answer 3

To use a variable, you must notify the compiler of the name and the type of the variable (declare the variable).

Back to Question 3

Answer 2

Answer 1

2
Listing 2: Listing for Answer 1.

/*File simple4.java
This application reads characters from the keyboard until 
encountering the # character and echoes each character to 
the screen. The program terminates when the user enters 
the # character.
**********************************************************/
class simple4 { //define the controlling class
  public static void main(String[] args) 
                               throws java.io.IOException {
    int ch1 = 0;
    System.out.println(
                      "Enter some text, terminate with #");
    while( (ch1 = System.in.read() ) != '#') 
      System.out.print((char)ch1);
    System.out.println("Goodbye");
  }//end main
}//End simple4 class.

Back to Question 1

Miscellaneous

This section contains a variety of miscellaneous information.

Note:

Housekeeping material
  • Module name: Jb0200r: Review: Variables
  • File: Jb0200r.htm
  • Published: 11/23/12
  • Revised: 01/02/13

Note:

Disclaimers:

Financial : Although the Connexions site makes it possible for you to download a PDF file for this module at no charge, and also makes it possible for you to purchase a pre-printed version of the PDF file, you should be aware that some of the HTML elements in this module may not translate well into PDF.

I also want you to know that, I receive no financial compensation from the Connexions website even if you purchase the PDF version of the module.

In the past, unknown individuals have copied my modules from cnx.org, converted them to Kindle books, and placed them for sale on Amazon.com showing me as the author. I neither receive compensation for those sales nor do I know who does receive compensation. If you purchase such a book, please be aware that it is a copy of a module that is freely available on cnx.org and that it was made and published without my prior knowledge.

Affiliation : I am a professor of Computer Information Technology at Austin Community College in Austin, TX.

-end-

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