White Space

1
White Space

• Spaces, blank lines, and tabs are collectively
  called white space and are used to separate words
  and symbols in a program
• Extra white space is ignored
• A valid Java program can be formatted many
  different ways
• Programs should be formatted to enhance
  readability, using consistent indentation

2
Comments

• Comments in a program are also called inline
  documentation
• They should be included to explain the purpose of
  the program and describe processing steps
• Java comments can take two forms
• // comment runs to the end of the line
• / comment runs to terminating symbol, even
  across line breaks /

3
Identifiers

• Identifiers are the words a programmer uses in a
  program
• Most identifiers have no predefined meaning
  except as specified by the programmer
• An identifier can be made up of letters, digits,
  the underscore character (_), and the dollar sign
  
• They cannot begin with a digit
• Java is case sensitive, therefore Total and total
  are different identifiers

4
Reserved Words

• Some identifiers, called reserved words, have
  specific meanings in Java and cannot be used in
  other ways
• abstract boolean break byte
  byvalue case cast catch char
  class const continue default
  do double else extends
  false final finally float for
  future generic goto if
  implements import inner instanceof
  int interface long native
  new null operator outer
  package private protected public
  rest return short static
  super switch synchronized this
  throw throws transient true
  try var void volatile while

5
Literals

• A literal is an explicit data value used in a
  program
• Integer literals 25 69 -4288
• Floating point literals 3.14159 42.075 -0.5
  
• String literals "The result is " "To
  thine own self be true."

6
The Java API

• The Java Application Programmer Interface (API)
  is a collection of classes that can be used
  as needed
• The println and print methods are part of the
  Java API they are not part of the Java
  language itself
• Both methods print information to the screen
  the difference is that println moves to the
  next line when done, but print does not
• See Countdown.java

7
Errors

• A program can have three types of errors
• The compiler will find problems with syntax and
  other basic issues (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
  (logical errors)

8
Command Line Arguments

• See Name_Tag.java
• The main method accepts extra information on the
  command line when a program is executed
• gt java Name_Tag John
• Each extra value is called command line argument
  
• In Java, command line arguments are always read
  as a list of character strings

9
Object-Oriented Programming

• Java is object-oriented language
• Programs are made from software components called
  objects
• An object contains data and methods
• An object is defined by a class
• Multiple objects can be created from the same
  class

10
Object-Oriented Programming

• A class represents a concept and an object
  represents the realization of that concept
  
• Car Class Objects

11
Object-Oriented Programming

• Objects can also be derived from each other using
  a process called inheritance
• Objects, classes, and inheritance will be
  discussed in greater detail later

12
Class Libraries

• The Java API is a class library, a group of
  classes that support program development
  Classes in a class hierarchy are often related by
  inheritance
• The classes in the Java API is separated into
  packages
• The System class, for example, is in package
  java.lang
• Each package contains a set of classes that
  relate in some way

13
The Java API Packages

• Some packages in the Java API
• java.applet java.awt
• java.beans java.io
• java.security java.sql
• java.lang java.math
• java.net java.rmi
• java.text java.util
• java.lang package free gift

14
Importing Packages

• Using a class from the Java API can be
  accomplished by
• using its fully qualified name
• java.lang.System.out.println ()
• Or, the package can be imported using an
  import statement, which has two forms
• import java.applet.
• import java.util.Random
• The java.lang package is automatically imported
  into every Java program

15
Primitive Data Types

• A data type is defined by a set of values and the
  operators you can perform on them
• Each value stored in memory is associated with a
  particular data type
• The Java language has several predefined types,
  called primitive data types. The following
  reserved words represent eight different
  primitive types
• byte, short, int, long, float, double, boolean,
  char

16
Integers

• There are four separate integer primitive data
  types They differ by the amount of memory
  used to store them Type byte
  short int long Storage 8
  bits 16 bits 32 bits 64 bits
  Min Value -128 -32,768
  -2,147,483,648 lt -9 x 1018 Max Value
  127 32,767 2,147,483,647 gt
  9 x 1018

17
Boolean

• A boolean value represents a true or false
  condition
• They can also be used to represent any two
  states, such as a light bulb being on or off
  
• The reserved words true and false are the
  only valid values for a boolean type

18
Characters

• The ASCII character set is still the basis for
  many other programming languages
• ASCII is a subset of Unicode, 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, ...

19
Wrappers

• For each primitive data type there is a
  corresponding wrapper class.
• For example Wrapper classes are useful in
  situations where you need an object instead of a
  primitive type They also contain some
  useful methods Primitive Type int
  double char boolean
  Wrapper Class Integer Double
  Character Boolean

20
Numeric Input

• Converting a string that holds an integer into
  the integer value can be done with a method in
  the Integer wrapper class valueInteger.parseInt
  (my_string)
• A value can be read and converted in one line
  num
• Integer.parseInt (stdin.readLine())

21
Expressions

• An expression is a combination of operators and
  operands
• The arithmetic operators include addition (),
  subtraction (-),multiplication (), and division
  (/)
• Operands can be literal values, variables, or
  other sources of data
• The programmer determines what is done with the
  result of an expression (stored, printed, etc.)

22
Operator Precedence

• The order in which operands are evaluated in an
  expression is determined by a well-defined
  precedence hierarchy Operators at the same
  level of precedence are evaluated according
  to their associativity (right to left or left to
  right) Parentheses can be used to force
  precedence Appendix D contains a complete
  operator precedence chart for all Java
  operators

23
The if Statement

• The Java if statement has the following
  syntax if (condition) statement
  If the boolean condition is true, the
  statement is executed if it is false, the
  statement is skipped This provides basic
  decision making capabilities

24
Block Statements

• Several statements can be grouped together into
  a block statement
• Blocks are delimited by braces
• A block statement can be used wherever a
  statement is called for in the Java syntax

25
The if-else Statement

• An else clause can be added to an if statement to
  make it an if-else statement if
  (condition) statement1 else
  statement2 If the condition is true,
  statement1 is executed if the condition is
  false, statement2 is executed See
  Temperature3.java and Right_Triangle.java

26
Nested if Statements

• The body of an if statement or else clause can be
  another if statement These are called
  nested if statements See
  Football_Choice.java Note an else clause
  is matched to the last unmatched if (no
  matter what the indentation implies)

27
The while Statement

• A while statement has the following syntax
  while (condition) statement If
  the condition is true, the statement is executed
  then the condition is evaluated again
  The statement is executed over and over until the
  condition becomes false

28
The while Statement

• If the condition of a while statement is false
  initially, the statement is never executed
  Therefore, we say that a while statement
  executes zero or more times

29
Infinite Loops

• The body of a while loop must eventually make the
  condition false If not, it is an
  infinite loop, which will execute until the user
  interrupts the program This is a
  common type of logical error -- always double
  check that your loops will terminate
  normally See Forever.java

30
Program Development

• The creation of software involves four basic
  activities
• establishing the requirements
• creating a design
• implementing the code
• testing the implementation
• The development process is much more involved
  that this, but these basic steps are a good
  starting point

31
Requirements

• Requirements specify the tasks a program must
  accomplish (what to do, not how to do it)
• They often address the user interface
• An initial set of requirements are often
  provided, but usually must be critiqued,
  modified, and expanded
• It is often difficult to establish detailed,
  unambiguous, complete requirements
• Careful attention to the requirements can save
  significant time and money in the overall project

32
Design

• A program follows an algorithm, which is a
  step-by-step process for solving a problem
• The design specifies the algorithms and data
  needed
• In object-oriented development, it establishes
  the classes, objects, and methods that are
  required
• The details of a method may be expressed in
  pseudo-code, which is code-like, but does not
  necessarily follow any specific syntax

33
Implementation

• Implementation is the process of translating a
  design into source code
• Most novice programmers think that writing code
  is the heart of software development, but it
  actually should be the least creative
• Almost all important decisions are made during
  requirements analysis and design
• Implementation should focus on coding details,
  including style guidelines and documentation

34
Testing

• A program should be executed multiple times with
  various input in an attempt to find errors
• Debugging is the process of discovering the cause
  of a problem and fixing it
• Programmers often erroneously think that there is
  "only one more bug" to fix
• Tests should focus on design details as well as
  overall requirements