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

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

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

Answer 3

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

Answer 4

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

Answer 5

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

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

Describe the purpose of the type definition in Java.

Answer 8

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

Answer 9

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

Answer 10

What are the two major categories of types in Java?

Answer 11

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

Answer 12

List the primitive types in Java.

Answer 13

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

Answer 14

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

Answer 15

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

Answer 16

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

Answer 17

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

Answer 18

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

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

Answer 20

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

Answer 21

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

Answer 22

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

What is a legal identifier in Java?

Answer 24

What are the rules for variable names in Java?

Answer 25

What is meant by the scope of a Java variable?

Answer 26

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

Answer 27

What is a member variable?

Answer 28

Where are local variables declared in Java?

Answer 29

What is the scope of a local variable in Java?

Answer 30

What defines a block of code in Java?

Answer 31

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

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

What are method parameters and what are they used for?

Answer 34

What is the scope of a method parameter ?

Answer 35

What are exception handler parameters ?

Answer 36

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

Answer 37

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

Answer 38

How are method parameters initialized in Java?

Answer 39

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

Back to Question 39

True.

Back to Question 38

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

Back to Question 37

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

Back to Question 36

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

Back to Question 35

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

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:

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

Back to Question 33

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

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

{ ... } .

Back to Question 31

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

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

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

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

Back to Question 27

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

Back to Question 26

The rules for Java variable names are as follows:

Back to Question 25

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

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

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

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

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 .

Double myWrappedData = new Double(5.5);

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

Double myWrappedData = 5.5;

Back to Question 21

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

double myPrimitiveData = 5.5;

Back to Question 20

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

Wrapper classes

Back to Question 18

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

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

Back to Question 16

True.

Back to Question 15

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

Back to Question 14

Back to Question 13

Primitive types contain a single value.

Back to Question 12

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

Back to Question 11

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

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

Back to Question 9

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

The syntax is shown in boldface below:

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

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

Back to Question 6

int firstVariable, secondVariable = 10; 

Back to Question 5

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

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

variable

Back to Question 2

/*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