Chapter 1 – Getting Started

Question 1

intermediate language

Answer 1

An intermediate language is an abstract programming language used by a compiler as an in-between step when translating a computer program into machine code. Before compiling the program into code for an actual, physical machine, the compiler first translates it into intermediate code suitable for a theoretical, abstract machine. This code is analyzed by the compiler, and if any opportunities for optimization are identified the compiler can perform the optimizations when making the translation into assembly language.

Question 2

Java byte-code (aka byte-code)

Answer 2

An intermediate language that Java code is translated into. Java bytecode is the instruction set of the Java virtual machine (JVM).

Question 3

code

Answer 3

A program or a part of a program.

Question 4

object-oriented programming (OOP)

Answer 4

OOP is a programming methodology that views a program as consisting of objects that interact with each other by means of actions.

Question 5

object

Answer 5

An object can be a variable, a data structure, a function, or a method, and as such, is a value in memory referenced by an identifier.

Question 6

method

Answer 6

Actions that an object can take are called the methods of that object.

Question 7

class

Answer 7

Objects of the same kind or that have the same type. For example, all of the airplanes in a flight simulation game might be of the same class, but they are different instances of that class.

Question 8

application program

Answer 8

A class with a method named main; when you run the Java program, the run-time system automatically invokes the method named main (that is, it automatically initiates the main action).

Question 9

applet

Answer 9

A little Java application, applets and applications are almost identical. The difference is that applications are meant to be run on your computer like any other program, whereas an applet is meant to be run from a Web browser, and so can be sent to another location on the Internet and run there. Applets always use a windowing interface, but not all programs with a windowing interface are applets.

Question 10

application

Answer 10

An application, or application program, is just a regular program. That is, computer software designed to help the user to perform specific tasks.

Question 11

applet viewer

Answer 11

Although applets are designed to be run via a Web browser, they can also be run via this thing, which is typically meant to be for debugging purposes.

Question 12

System.out.println

Answer 12

A method in the System.out framework that prints the text in its argument with a new line character (“\n”) attached at the end.

Question 13

invoking

Answer 13

hen an object performs an action using a method, it is called invoking (or calling) the method.

Question 14

dot

Answer 14

In a Java program, you write such a method invocation by writing the object followed by a dot (period), followed by the method name, and some parentheses that may or may not have something inside them.

Question 15

argument

Answer 15

The thing (or things) inside the parentheses is called an argument(s), which provides information needed by the method to carry out its action.

Question 16

sending a message

Answer 16

Another term for invoking a method is to send a message to the object. With this view, a message is sent to the object (by invoking a method) and in response, the object performs some action (namely, the action taken by the method invoked).

Question 17

variable int

Answer 17

A variable declaration that contains only integers. So for example, the following code declares the variable var and says that it can only take integer values (say 2, or -7):
> int var;

Question 18

equal sign / assignment operator

Answer 18

The equal sign (=) is used in Java as the assignment operator. This operator assigns the value to its right to the variable on its left. For example, the following will declare var as a variable integer and assign 7 - 9 to it:
> int var = 7 - 9;

Question 19

high-level, low-level, and machine languages

Answer 19

A high-level programming language is a language designed to be (relatively) easy for people to write and understand. Machine languages are the languages that computers can directly understand. Machine languages and things like them are called low-level languages.

Question 20

compiler

Answer 20

A compiler is a program that translates a high-level language program, such as a Java program, into an equivalent low-level-language program.

Question 21

Java Virtual Machine (JVM)

Answer 21

Bytecode is not the machine language for any particular computer; it is the machine language for a fictitious computer called the Java Virtual Machine (JVM). A Java virtual machine (JVM) is (also) a virtual machine that enables a computer to run Java programs as well as programs written in other languages that are also compiled to Java bytecode.

Question 22

interpreter

Answer 22

One of the ways to implement the JVM, an interpreter combines the translation of the bytecode and the execution of the corresponding machine language instructions. The interpreter works by translating an instruction of bytecode into instructions expressed in your computer’s machine language and then executing those instructions on your computer. It does this one bytecode instruction at a time. Thus, an interpreter translates and executes the instructions in the bytecode one after the other, rather than translating the entire bytecode program at once.

Question 23

Just-In-Time (JIT)

Answer 23

Modern implementations of the JVM use a JIT compiler, which uses a combination of interpretation and compilation. The JIT compiler reads the bytecode in chunks and compiles entire chunks to native machine language instructions as needed. The compiled machine language instructions are remembered—that is, cached—for future use, so the chunk needs to be compiled only once. This model generally runs programs faster than the interpreted model, which always has to translate the next bytecode instruction to machine code instructions.

Question 24

run command

Answer 24

A command that executes the JVM on the bytecode.

Question 25

source code

Answer 25

The original code before it is compiled into bytecode.

Question 26

object code

Answer 26

The bytecode (or really any intermediate language code) generated by a compiler.

Question 27

.java files

Answer 27

These are files that hold the source code which will be compiled into object code.

Question 28

javac

Answer 28

This is a command that compiles its argument from a .java file (source code) to a .class file (object code). For example:
> javac program.java

Question 29

.class files

Answer 29

When you compile a Java class, the resulting bytecode for that class is placed in a .class file of the same name, except that the ending is changed from .java to .class. So, files when you compile a class named FirstProgram in the file FirstProgram.java, the resulting bytecode is stored in a file named FirstProgram.class.

Question 30

bug

Answer 30

A mistake in a program is called a bug.

Question 31

debugging

Answer 31

The process of eliminating mistakes in your program.

Question 32

syntax error

Answer 32

A syntax error is a grammatical mistake in your program; that is, a mistake in the allowed arrangement of words and punctuations. If you violate one of these rules—for example, by omitting a required punctuation—it is a syntax error. The compiler will catch syntax errors and output an error message telling you that it has found the error, where it thinks the error is, and what it thinks the error is. If the compiler says you have a syntax error, you undoubtedly do. However, the compiler could be incorrect about where and what the error is.

Question 33

run-time error

Answer 33

An error that is not detected until your program is run is called a run-time error. If the computer detects a run-time error when your program is run, then it will output an error message. The error message may not be easy to understand, but at least it lets you know that something is wrong.

Question 34

logic error

Answer 34

A mistake in the underlying algorithm for your program is called a logic error. If your program has only logic errors, it will compile and run without any error message. You have written a valid Java program, but you have not written a program that does what you want. The program runs and gives output, but the output is incorrect.

Question 35

identifier

Answer 35

The name of a variable (or other item you might define in a program).

Question 36

case-sensitive

Answer 36

Java is a case-sensitive language; that is, it distinguishes between upper- and lowercase letters in the spelling of identifiers.

Question 37

keyword (aka reserved words)

Answer 37

There is a special class of identifiers, called keywords or reserved words, that have a predefined meaning in Java and that you cannot use as names for variables or anything else.

Question 38

declare

Answer 38

Every variable in a Java program must be declared before it is used. When you declare a variable, you are telling the compiler—and, ultimately, the computer—what kind of data you will be storing in the variable.

Question 39

floating-point number

Answer 39

A number that has a decimal point. Decimals are represented with the double type in Java.

Question 40

primitive types

Answer 40

Java has basic types for characters, different kinds of integers, and different kinds of floating-point numbers (numbers with a decimal point), as well as a type for the values true and false. These basic types are known as primitive types. Here’s all of them: boolean, char, byte, short, int, long, float, double.

Question 41

assignment statement

Answer 41

The most direct way to change the value of a variable. This kind of statement has the following form:
> = ;
where is a literal that is interpreted appropriately for the type of .

Question 42

uninitialized variable

Answer 42

A variable that has been declared but that has not yet been given a value by some means, such as an assignment statement, is said to be uninitialized. For example:
> int variable;

Question 43

assigning int values to double variables

Answer 43

There are some special cases where it is permitted to assign a value of one type to a variable of another type. It is acceptable to assign a value of an integer type, such as int, to a variable of a floating-point type, such as the type double.

Question 44

integers and booleans

Answer 44

In many languages other than Java, you can assign integers to variables of type boolean and assign boolean values to integer variables. You cannot do that in Java. In Java, the boolean values true and false are not integers nor will they be automatically converted to integers. (In fact, it is not even legal to do an explicit type cast from the type boolean to the type int or vice versa. Explicit type casts are discussed later in this chapter in the subsection “Type Casting.”)

Question 45

constants (or literals)

Answer 45

Constants are things that don’t change in value. For example, 2.5. A literal is essentially a constant as it is written in the program. For example, “2.5” is a literal in the expression:
> double variable = 2.5;

Question 46

e notation

Answer 46

A more complicated notation for floating-point constants, such as constants of type double, is called scientific notation or floating-point notation and is particularly handy for writing very large numbers and very small fractions. For instance, in Java, we represent 2.5 * 10^5 as:
> double variable = 2.5e5;

Question 47

quotes and literal Strings, chars

Answer 47

In Java, a literal String expression contains the string in double quotes. For example:
>String myString = “bob”;
On the contrary, the char type has its literal in single quotes:
>char myChar = ‘b’;

Question 48

mixing types (e.g., what happens when you do x + y when x is an int and y is a double?)

Answer 48

In Java, some types can be mixed during arithmetic operations. The type that an arithmetic operation results in is the rightmost type in the expression as it appears in this list:
byte, short, int, long, float, double.
For example, if an int is added to a float, you will get a float.

Question 49

integer division

Answer 49

When used with two operands of type int, the division operator yields the integer part resulting from division. In other words, integer division discards the part after the decimal point. So, 10/3 is 3.

Question 50

the % operator

Answer 50

The operator % can be used with operands of type int to recover the information lost when you use / to do division with numbers of type int. x % y gives you the remainder of x / y.

Question 51

type coercion

Answer 51

An automatic, or implicit, type cast. For example, in the following code, “5” is an int that is typecasted to “5.0,” a double:
> double d = 5;

Question 52

v++ versus ++v

Answer 52

Notice that the two increment operators n++ and ++n have the exact same effect on a variable n: They both increase the value of n by one. But the two expressions evaluate to different values. Remember, if the ++ is before the variable, then the incrementing is done before the value is returned; if the ++ is after the variable, then the incrementing is done after the value is returned.

Question 53

decrement operator

Answer 53

Both n−− and −−n change the value of n by subtracting one, but they evaluate to different values. n−− evaluates to the value n had before it was decremented; on the other hand, −−n evaluates to the value n has after it is decremented.

Question 54

String

Answer 54

There is no primitive type for strings in Java. However, there is a class called String that can be used to store and process strings of characters. This section introduces the class String.

Question 55

+ operator (w/ strings)

Answer 55

When you use the + operator on two strings, the result is the string obtained by connecting the two strings to get a longer string.

Question 56

concatenation

Answer 56

The string obtained by connecting the two strings to get a longer string. To concatenate s1 and s2 in Java, do:
> s1 + s2;

Question 57

method call or method invocation

Answer 57

Classes are central to Java, and you will soon be defining and using your own classes. A class is the name for a type whose values are objects. Objects are entities that store data and can take actions. For example, objects of the class String store data consisting of strings of characters, such as "Hello". The actions that an object can take are called methods. So to call the method length() on a string, do the following (Dot notation):
> "Hello".length();

Question 58

calling object

Answer 58

The object before the dot is known as the calling object in method invocation. In the following example, the string s:
> String s = “Hello”;
> s.length();

Question 59

position

Answer 59

Some methods for the class String depend on counting positions in the string. Positions are counted starting with 0, not with 1. So, in the string “Surf time”, ‘S’ is in position 0, ‘u’ is in position 1, and so forth.

Question 60

index

Answer 60

A position is usually referred to as an index. So, it would be preferable to say: ‘S’ is at index 0, ‘u’ is at index 1, and so on.

Question 61

backslash \

Answer 61

A backslash, \, preceding a character tells the compiler that the character following the \ does not have its usual meaning.

Question 62

escape sequence

Answer 62

A sequence of characters that starts with a backslash \ is called an escape sequence or an escape character. The sequence is typed in as two characters with no space between the symbols. Several escape sequences are defined in Java.
" Double quote.
' Single quote.
\ Backslash.
\n New line. Go to the beginning of the next line.
\r Carriage return. Go to the beginning of the current line. \t Tab. White space up to the next tab stop.

Question 63

What does it mean to say that strings in Java are immutable objects?

Answer 63

In Java, an object of type String is an immutable object, meaning that the characters in the String object cannot be changed.

Question 64

ASCII

Answer 64

The ASCII character set is simply a list of all the characters normally used on an English-language keyboard plus a few special characters. In this list, each character has been assigned a number so that characters can be stored by storing the corresponding number.

Question 65

Unicode

Answer 65

The Unicode character set includes the ASCII character set plus many of the characters used in languages with a different alphabet from English.

Question 66

//comments

Answer 66

All of the text between the // and the end of the line is a comment. The compiler simply ignores anything that follows // on a line.

Question 67

line comments

Answer 67

The symbols // are two slashes (without a space between them). Comments indicated with // are often called line comments or inline comments.

Question 68

/comments/

Answer 68

There is another way to insert comments in a Java program. Anything between the symbol pair /* and the symbol pair / is considered a comment and is ignored by the compiler. Unlike the // comments, which require an additional // on each line, the / to */ comments can span several lines.

Question 69

block comments

Answer 69

Comments of the /* */ type are often called block comments.

Question 70

when to comment

Answer 70

It is difficult to say just how many comments a program should contain. The only correct answer is “just enough,” which of course conveys little to the novice programmer. It will take some experience to get a feel for when it is best to include a comment. Whenever something is important and not obvious, it merits a comment. However, providing too many comments is as bad as providing too few. A program that has a comment on each line is so buried in comments that the structure of the program is hidden in a sea of obvious observations.

Question 71

self-documenting

Answer 71

A well-written program is called self-documenting, which means that the structure of the program is clear from the choice of identifier names and the indenting pattern. A completely self-documenting program would need none of these // comments that are only for the programmer who reads or modifies the code. That may be an ideal that is not always realizable, but if your code is full of // comments and you follow our convention on when to use them, then either you simply have too many comments or your code is poorly designed.

Question 72

class loader

Answer 72

A Java program is divided into smaller parts called classes, and normally each class definition is in a separate file and is compiled separately. In order to run your program, the bytecode for these various classes needs to be connected together. The connecting is done by a program known as the class loader.