Sample Quiz Answers
For Chapter 1
THIS PAGE CONTAINS SAMPLE ANSWERS to the Quiz on
Chapter 1 of this on-line
Java textbook. Note that in many cases, there are lots of correct
answers to a given question.
Question 1:
One of the components of a computer is its CPU. What is a
CPU and what role does it play in a computer?
Answer:
The CPU, or Central Processing Unit, is the active part of the computer. Its
function is to execute programs that are coded in machine language and stored
in the main memory (RAM) of the computer. It does this by repeating the
fetch-and-execute cycle over and over; that is, it repeatedly fetches a machine
language instruction from memory and executes it.
Question 2:
Explain what is meant by an "asynchronous event." Give some examples.
Answer:
An asynchronous event is one that occurs at an unpredictable time
outside the control of the program that the CPU is running. It is not "synchronized"
with the program. An example would be when the user presses a key on the keyboard or
clicks the mouse button. (These events generate "interrupts" that cause the
CPU to interrupt what it is doing and to take some action to handle the asynchronous
event. After handling the event, the CPU returns to what it was doing before it was
interrupted.)
Question 3:
What is the difference between a "compiler" and an "interpreter"?
Answer:
Compilers and interpreters have similar functions: They take a program
written in some programming language and translate it into machine language. A compiler
does the translation all at once. It produces a complete machine language program that
can then be executed. An interpreter, on the other hand, just translates one instruction
at a time, and then executes that instruction immediately. (Java uses a compiler
to translate java programs into Java Bytecode, which is a machine language for the
imaginary Java Virtual Machine. Java Bytecode programs are then executed by an
interpreter.)
Question 4:
Explain the difference between high-level languages
and machine language.
Answer:
Programs written in the machine language of a given type of computer
can be directly executed by the CPU of that type of computer. High-level
language programs must be translated into machine language before they
can be executed. (Machine language instructions are encoded as binary
numbers that are meant to be used by a machine, not read or written
by people. High-level languages use a syntax that is closer to
human language.)
Question 5:
If you have the source code for a Java program, and you want to
run that program, you will need both a compiler and an
interpreter. What does the Java compiler do, and
what does the Java interpreter do?
Answer:
The Java compiler translates Java programs into a language called Java
bytecode. Although bytecode is similar to machine language, it
is not the machine language of any actual computer. A Java
interpreter is used to run the compiled Java bytecode program.
(Each type of computer needs its own Java bytecode interpreter,
but all these interpreters interpret the same bytecode language.)
Question 6:
What is a subroutine?
Answer:
A subroutine is a set of instructions for performing some task
that have been grouped together and given a name. Later, when
that task needs to be performed, it is only necessary to
call the subroutine by giving its name, rather than
repeating the whole sequence of instructions.
Question 7:
Java is an object-oriented programming language. What is an object?
Answer:
An object consists of some data together with a set of subroutines that
manipulate that data. (An object is a kind of "module," or self-contained
entity that communicates with the rest of the world through a well-defined
interface. An object should represent some coherent concept or
real-world object.)
Question 8:
What is a variable? (There are four different ideas associated
with variables in Java. Try to mention all four aspects in your answer.
Hint: One of the aspects is the variable's name.)
Answer:
A variable is a memory location that has been given a name
so that it can easily be referred to in a program. The variable holds
a value, which must be of some specified type. The value
can be changed during the course of the execution of the program.
Question 9:
Java is a "platform-independent language." What does this mean?
Answer:
A Java program can be compiled once into a Java Bytecode program.
The compiled program can then be run on any computer that has an interpreter for the
Java virtual machine. Other languages have to be re-compiled for each platform
on which they are going to run. The point about Java is that it can be executed on
many different types of computers without being recompiled.
Question 10:
What is the "Internet"? Give some examples of how it is used. (What kind
of services does it provide?)
Answer:
The Internet is a network connecting millions of computers
around the world. Computers connected to the Internet can communicate with
each other. The Internet can be used for Telnet (which lets a user of one
computer log onto another computer remotely), FTP (which is used to copy
files between computers), and the World Wide Web (which lets a user view
"pages" of information published on computers around the world).
