Chapter 3

Question 1

What is the primary task when writing a Java program?

Answer 1

Defining a set of classes that your program will use

Question 2

What statement would you use if you wanted to create a variable called “name” which held the text string, “Joe”?

Answer 2

String name = new String(“Joe”);

Question 3

What is the name of the class that is typically used to divide a string into shorter strings called tokens?

Answer 3

StringTokenizer

it’s in the java.util package

Question 4

What do we call the special method that gets called when you use the “new” operator to create an object of a class?

Answer 4

a constructor

Question 5

How does Java handle “garbage collection”?

Answer 5

Java automatically clears memory of any objects that are no longer in use.

Question 6

Using dot notation, how would you refer to a variable called “driver” in an object called “car”?

Answer 6

car.driver

Question 7

If the driver of a car was represented in dot notation as “car.driver”, how could you represent the age of that driver?

Answer 7

car.driver.age

this is called “chaining”

Question 8

What statement would you use to declare a class variable called lastName and assign a value of “Jones” to it?

Answer 8

static String lastName = “Jones”;

static is the keyword that specifies the variable is a class variable

Question 9

When retrieving or changing the value of a class variable, how do you refer to that variable using dot notation?

Answer 9

[object instance].[variable]
OR
[class].[variable]

(For readability, the second method is preferable since it is, after all, a class variable]

Question 10

When reading code, what distinguishes methods from other program elements?

Answer 10

parentheses

Example: cancelOrder()

Question 11

What method can be used to print a number in currency format?

Answer 11

System.out.format( );

In the parentheses, you use a percent sign followed by one or more letter flags, then a comma and the variable to be formatted.

Question 12

What is an object reference?

Answer 12

An address indicating where the object’s variables and methods are stored

Question 13

What special flexibility does Java demonstrate when processing a group of concatenated variables where at least one of them is a string?

Answer 13

Java treats the whole group as a String.

Question 14

What is casting?

Answer 14

Converting a value from one data type to another

Question 15

Which primitive data type can not be cast to any other data type?

Answer 15

Booleans

Question 16

How do you cast a value or expression to another data type?

Answer 16

(typename) value

Question 17

What statement would you use to cast the result of expression “x / y” to an int data type, and store that result in a variable called “result”?

Answer 17

int result = (int)( x / y);

Question 18

What conditions must apply to be able to cast an object into an object of another class?

Answer 18

One class must be a subclass of the other

Question 19

When you cast a superclass object as an object of a subclass, what does the object gain?

Answer 19

All the methods and variables that the subclass defines

Question 20

Write a statement that will cast “emp”, an object of the Employee class, as an object of the VicePresident class, into the “veep” variable.

Answer 20

veep = (VicePresident) emp;

Question 21

Is it possible to cast an object to a primitive data type, and a primitive data type to an object?

Answer 21

No.

Question 22

What is the difference between a double and a Double?

Answer 22

A double is a primitive data type. Double is a “wrapper” class in the java.lang package that allows you to work with a double as an object.