Download Java Programming

Chapter 1
Objects and Primitive data
1
Java

A programming language specifies the words and symbols
that we can use to write a program

A programming language employs a set of rules that dictate
how the words and symbols can be put together to form valid
program statements

The Java programming language was created by Sun
Microsystems, Inc.

It was introduced in 1995 and it's popularity has grown quickly
since
2
Futures of Java

Java is secure

Java is a platform –independent language

Java is an Internet programming language

Java is a high-performance language

Java is simple
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Java Program Structure

In the Java programming language:
 A program is made up of one or more classes
 A class contains one or more methods
 A method contains program statements

These terms will be explored in detail throughout the course

A Java application always contains a method called main

See Lincoln.java (page 28)
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Java Program Structure
//
comments about the class
public class MyProgram
{
class header
class body
Comments can be placed almost anywhere
}
5
Java Program Structure
//
comments about the class
public class MyProgram
{
//
comments about the method
public static void main (String[] args)
{
method body
method header
}
}
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Comments

Comments in a program are called inline documentation

They should be included to explain the purpose of the
program and describe processing steps

They do not affect how a program works

Java comments can take three forms:
// this comment runs to the end of the line
/*
this comment runs to the terminating
symbol, even across line breaks
/** this is a javadoc comment
*/
*/
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Identifiers

Identifiers are the words a programmer uses in a program

An identifier can be made up of letters, digits, the underscore
character ( _ ), and the dollar sign

Identifiers cannot begin with a digit

Java is case sensitive - Total, total, and TOTAL are
different identifiers

By convention, programmers use different case styles for
different types of identifiers, such as


title case for class names - Lincoln

upper case for constants – MAXIMUM
A reserved word cannot be used in any other way.
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Reserved Words

The Java reserved words:
abstract
assert
boolean
break
byte
case
catch
char
class
const
continue
default
do
double
else
enum
extends
false
final
finally
float
for
goto
if
implements
import
instanceof
int
interface
long
native
new
null
package
private
protected
public
return
short
static
strictfp
super
switch
synchronized
this
throw
throws
transient
true
try
void
volatile
while
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White Space

Spaces, blank lines, and tabs are called white space

White space is used to separate words and symbols in a
program

Extra white space is ignored

A valid Java program can be formatted many ways

Programs should be formatted to enhance readability, using
consistent indentation

See Lincoln2.java (page 34)

See Lincoln3.java (page 35)
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Program Development


The mechanics of developing a program include several
activities

writing the program in a specific programming language
(such as Java)

translating the program into a form that the computer can
execute

investigating and fixing various types of errors that can
occur
Software tools can be used to help with all parts of this
process
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Language Levels

There are four programming language levels:
 machine language
 assembly language
 high-level language
 fourth-generation language

Each type of CPU has its own specific machine language

The other levels were created to make it easier for a human
being to read and write programs
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Programming Languages

Each type of CPU executes only a particular machine
language

A program must be translated into machine language before
it can be executed

A compiler is a software tool which translates source code
into a specific target language

Often, that target language is the machine language for a
particular CPU type

The Java approach is somewhat different
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Java Translation

The Java compiler translates Java source code into a special
representation called bytecode

Java bytecode is not the machine language for any traditional
CPU

Another software tool, called an interpreter, translates
bytecode into machine language and executes it

Therefore the Java compiler is not tied to any particular
machine

Java is considered to be architecture-neutral
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Java Translation
Java source
code
Java
compiler
Java
bytecode
Bytecode
interpreter
Bytecode
compiler
Machine
code
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Errors

A program can have three types of errors

The compiler will find syntax errors and other basic problems
(compile-time errors)

If compile-time errors exist, an executable version of the
program is not created

A problem can occur during program execution, such as trying
to divide by zero, which causes a program to terminate
abnormally (run-time errors)

A program may run, but produce incorrect results, perhaps
using an incorrect formula (logical errors)
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Character Strings

A string of characters can be represented as a string literal by
putting double quotes around the text:

Examples:
"This is a string literal."
"123 Main Street"
"X"

Every character string is an object in Java, defined by the
String class

Every string literal represents a String object
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The println Method

In the Lincoln program, we invoked the println method to
print a character string

The System.out object represents a destination (the monitor
screen) to which we can send output
System.out.println ("Whatever you are, be a good one.");
object
method
name
information provided to the method
(parameters)
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The print Method

The System.out object provides another service as well

The print method is similar to the println method, except
that it does not advance to the next line

Therefore anything printed after a print statement will
appear on the same line

See Countdown.java (page 63)
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String Concatenation

The string concatenation operator (+) is used to append one
string to the end of another
"Peanut butter " + "and jelly"

It can also be used to append a number to a string

A string literal cannot be broken across two lines in a program

See Facts.java (page 65)
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String Concatenation

The + operator is also used for arithmetic addition

The function that it performs depends on the type of the
information on which it operates

If both operands are strings, or if one is a string and one is a
number, it performs string concatenation

If both operands are numeric, it adds them

See Addition.java (page 67)
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Escape Sequences


What if we wanted to print a the quote character?
The following line would confuse the compiler because it
would interpret the second quote as the end of the string
System.out.println ("I said "Hello" to you.");


An escape sequence is a series of characters that represents
a special character
An escape sequence begins with a backslash character (\)
System.out.println ("I said \"Hello\" to you.");
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Escape Sequences

Some Java escape sequences:
Escape Sequence
\b
\t
\n
\r
\"
\'
\\

Meaning
backspace
tab
newline
carriage return
double quote
single quote
backslash
See Roses.java (page 68)
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Primitive Data

There are eight primitive data types in Java

Four of them represent integers:


Two of them represent floating point numbers:


float, double
One of them represents characters:


byte, short, int, long
char
And one of them represents boolean values:

boolean
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Numeric Primitive Data

The difference between the various numeric primitive types
is their size, and therefore the values they can store:
Type
Storage
Min Value
Max Value
byte
short
int
long
8 bits
16 bits
32 bits
64 bits
-128
-32,768
-2,147,483,648
< -9 x 1018
127
32,767
2,147,483,647
> 9 x 1018
float
double
32 bits
64 bits
+/- 3.4 x 1038 with 7 significant digits
+/- 1.7 x 10308 with 15 significant digits
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Characters

A char variable stores a single character

Character literals are delimited by single quotes:
'a'

'X'
'7'
'$'
','
'\n'
Example declarations:
char topGrade = 'A';
char terminator = ';', separator = ' ';

Note the distinction between a primitive character variable,
which holds only one character, and a String object, which
can hold multiple characters.
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Character Sets

A character set is an ordered list of characters, with each
character corresponding to a unique number

A char variable in Java can store any character from the
Unicode character set

The Unicode character set uses sixteen bits per character,
allowing for 65,536 unique characters

It is an international character set, containing symbols and
characters from many world languages
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Characters

The ASCII character set is older and smaller than Unicode,
but is still quite popular

The ASCII characters are a subset of the Unicode character
set, including:
uppercase letters
lowercase letters
punctuation
digits
special symbols
control characters
A, B, C, …
a, b, c, …
period, semi-colon, …
0, 1, 2, …
&, |, \, …
carriage return, tab, ...
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Boolean

A boolean value represents a true or false condition

The reserved words true and false are the only valid
values for a boolean type
boolean done = false;

A boolean variable can also be used to represent any two
states, such as a light bulb being on or off
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Type Casting

In type casting, a data type is converted into another data
type.

Example
float c = 34.89675f;
int b = (int)c + 10;
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Automatic type and Casting



There are two type of data conversion: automatic type
conversion and casting.
When one type of data is assigned to a variable of another
type then automatic type conversion takes place provided it
meets the conditions specified:
 The two types are compatible
 The destination type is larger than the source type.
Casting is used for explicit type conversion. It loses
information above the magnitude of the value being
converted.
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Type Promotion Rules




All byte and short values are promoted to int type.
If one operand is long, the whole expression is promoted to
long.
If one operand is float then the whole expression is
promoted to float.
If one operand is double then the whole expression is
promoted to double.
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Variables




A variable is a name for a location in memory
Three components of a variable declaration are:
 Data type
 Name
 Initial value to be assigned (optional)
Syntax
datatype identifier [=value][, identifier[=value]...];
A variable can be given an initial value in the declaration
int sum = 0;
int base = 32, max = 149;

When a variable is referenced in a program, its current
value is used
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Scope and Lifetime of Variables






Variables can be declared inside a block.
The block begins with an opening curly brace and ends with
a closing curly brace.
A block defines a scope.
A new scope is created every time a new block is created.
Scope specifies what objects are visible to other parts of
the program.
It also determines the life of an object.
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Constants

A constant is an identifier that is similar to a variable except
that it holds the same value during its entire existence

As the name implies, it is constant, not variable

The compiler will issue an error if you try to change the value
of a constant

In Java, we use the final modifier to declare a constant
final int MIN_HEIGHT = 69;
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Operators






Arithmetic Operators
Bitwise Operators
Relational Operators
Logical Operators
Conditional Operators
Assignment operators
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Arithmetic Operators





Operands of the arithmetic operators must be of numeric type.
Boolean operands cannot be used, but character operands
are allowed.
These operators are used in mathematical expressions.
An expression is a combination of one or more operators and
operands
Arithmetic expressions compute numeric results and make
use of the arithmetic operators:
Addition
Subtraction
Multiplication
Division
Remainder

+
*
/
%
If either or both operands used by an arithmetic operator are
floating point, then the result is a floating point
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Division and Remainder


If both operands to the division operator (/) are integers, the
result is an integer (the fractional part is discarded)
14 / 3
equals
4
8 / 12
equals
0
The remainder operator (%) returns the remainder after
dividing the second operand into the first
14 % 3
equals
2
8 % 12
equals
8
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Operator Precedence

Operators can be combined into complex expressions
result
=
total + count / max - offset;

Operators have a well-defined precedence which
determines the order in which they are evaluated

Multiplication, division, and remainder are evaluated prior to
addition, subtraction, and string concatenation

Arithmetic operators with the same precedence are
evaluated from left to right, but parentheses can be used to
force the evaluation order
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Operator Precedence

What is the order of evaluation in the following expressions?
a + b + c + d + e
a + b * c - d / e
a / (b + c) - d % e
a / (b * (c + (d - e)))
a + b + c + d + e
1
2
3
4
a + b * c - d / e
3
1
4
2
a / (b + c) - d % e
2
1
4
3
a / (b * (c + (d - e)))
4
3
2
1
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Expression Trees


The evaluation of a particular expression can be shown using
an expression tree
The operators lower in the tree have higher precedence for
that expression
+
a + (b – c) / d
/
a
b
d
c
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Increment and Decrement

The increment and decrement operators use only one operand

The increment operator (++) adds one to its operand

The decrement operator (--) subtracts one from its operand

The statement
count++;
is functionally equivalent to
count = count + 1;
42
Increment and Decrement

The increment and decrement operators can be applied in
postfix form:
count++

or prefix form:
++count

When used as part of a larger expression, the two forms can
have different effects

Because of their subtleties, the increment and decrement
operators should be used with care
43
Assignment Operators

Often we perform an operation on a variable, and then store
the result back into that variable

Java provides assignment operators to simplify that process

For example, the statement
num += count;
is equivalent to
num = num + count;
44
Assignment Operators

There are many assignment operators in Java, including the
following:
Operator
+=
-=
*=
/=
%=
Example
x
x
x
x
x
+=
-=
*=
/=
%=
y
y
y
y
y
Equivalent To
x
x
x
x
x
=
=
=
=
=
x
x
x
x
x
+
*
/
%
y
y
y
y
y
45
Assignment Operators

The behavior of some assignment operators depends on the
types of the operands

If the operands to the += operator are strings, the assignment
operator performs string concatenation

The behavior of an assignment operator (+=) is always
consistent with the behavior of the corresponding operator (+)
46
Class Libraries




A class library is a collection of classes that we can use when
developing programs
There is a Java standard class library that is part of any Java
development environment
These classes are not part of the Java language per se, but
we rely on them heavily
The System class and the String class are part of the Java
standard class library
47
Packages


The classes of the Java standard class library are organized
into packages
Some of the packages in the standard class library are:
Package
Purpose
java.lang
java.applet
java.awt
javax.swing
java.net
java.util
General support
Creating applets for the web
Graphics and graphical user interfaces
Additional graphics capabilities and components
Network communication
Utilities
48
The import Declaration

When you want to use a class from a package, you could use
its fully qualified name
java.util.Random

Or you can import the class, then just use the class name
import java.util.Random;

To import all classes in a particular package, you can use the *
wildcard character
import java.util.*;
49
The import Declaration


All classes of the java.lang package are automatically
imported into all programs
That's why we didn't have to explicitly import the System or
String classes in earlier programs

The Random class is part of the java.util package

It provides methods that generate pseudo-random numbers
50
Input/Output


To print output to the "standard output stream" just by calling
System.out.println
To read input from the console window you first construct a
Scanner that is attached to the "standard input stream"
System.in.
Scanner in = new Scanner(System.in);

The Scanner class provides convenient methods for reading
input values of various types

A Scanner object can be set up to read input from various
sources, including the user typing values on the keyboard

Keyboard input is represented by the System.in object

The new operator creates the Scanner object
51
Input/Output (cont)

Once created, the Scanner object can be used to invoke
various input methods of Scanner class, such as:
in.nextLine();
in.next();
in.nextInt();


in.nextdouble();
The Scanner class is part of the java.util class library,
and must be imported into a program to be used
See Echo.java (page 91)
52
Thank you for your attention!
53