CSC 332 Algorithms and Data Structures

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CSC 332 Algorithms and Data Structures

• Java Overview

Dr. Paige H. Meeker Computer Science Presbyterian
College, Clinton, SC
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Answers to previous assignment

• Problem 1
• Create a class called LeapYear that will accept
  console input from the user of a year and return
  a statement (true or false) if that year is a
  leap year.
• Sample output
• What year would you like to test?
• ltuser inputgt 1984
• It is true that 1984 is a leap year.

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Calculating Leap Years

• public boolean isLeap(int year)
• if ((year 100) 0)
• if ((year 400) 0) return true
• else return false
• if ((year 4) 0) return true
• return false

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Answers to previous assignment

• Problem 2
• Write a program to determine all pairs of
  positive integers, (a,b), such that
• a lt b lt 1000
• (a2 b2 1)/(ab) is an integer.

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Positive Integer Calculation

• for (int i 1 i lt 1000 i)
• for (int j 1 j lt 1000 j)
• if (i lt j)
• int a ii
• int b jj
• if (((ab1)(ij)) 0)
• System.out.println ("a "i" b
  "j)

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Answers to previous assignment

• Problem 3
• Create a class called Roman that will accept
  console input from the user of an integer and
  return its Roman numeral equivalent.
• For conversion information, see
• http//www.yourdictionary.com/crossword/romanums.h
  tml
• http//www.novaroma.org/via_romana/numbers.html

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Roman Numeral Calculation

• private static int numbers 1000, 900, 500,
  400, 100, 90, 50, 40, 10, 9, 5, 4, 1
• private static String letters "M", "CM",
  "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V",
  "IV", "I"
• public String convert(int arabic)
• String roman ""
• for (int i 0 i lt numbers.length i)
• while (arabic gt numbersi)
• roman lettersi
• arabic - numbersi
• return roman

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Lecture 2 Java Overview

• Primitive Java
• Reference Types
• Objects and Classes
• Inheritance

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Primitive Java

• Conditional Statements
• Relational and Equality Operators
• Logical Operators
• if
• while
• for
• do
• break and continue
• Switch
• Methods

• Comments
• main
• Primitive Types
• Constants
• Declaration and Initialization of Primitive Types
• Basic Operators
• Assignment
• Binary
• Unary
• Type Conversions

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Reference Types

• Define
• Basics
• Dot operator
• Declaration
• vs
• Parameter passing
• Strings
• Arrays
• Exceptions
• I/O

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Objects and Classes

• Definition
• Javadoc
• Basic Methods
• Constructors
• Mutator/Accessor
• toString(), equals()
• main()
• Static
• this
• instanceOf
• Packages
• Creating / Importing

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Inheritance

• Definition
• Hierarchies
• Type compatibility
• Super and Final
• Overriding vs Overloading
• Abstract methods / Classes
• Multiple Inheritance
• Interface
• Generic Components

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Primitive Java Basics to Begin With

• Java code lives in files that end in .java
• Compiler is javac
• javac generates bytecode found in .class files
• Bytecodes are portable, interpreted by the Java
  interpreter java aka the Java Virtual Machine

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Primitive Java Basics to Begin With

• The name of the source file must match the name
  of the class, including case conventions.

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Primitive JavaComments

• // indicates a single line comment
• / indicates a multi-line comment /
• / indicates a comment that provides information
  to the javadoc utility to generate documentation
  from the comments /
• Well commented code is the sign of a good
  programmer!!

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Primitive JavaPrimitive Types

• 8 primitive types
• byte
• short
• int
• long
• float
• double
• char
• boolean

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Primitive JavaConstants

• Integer constants can be represented in decimal,
  octal, or hexadecimal notation
• Character constants are enclosed in single quotes
• String constants are enclosed in double quotes

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Primitive JavaDeclaration and Initialization of
Primitive Types

• Variables declared by providing
• Name
• Type
• (Hopefully) Initial Value
• Name must be an identifier
• Any combination of letters/digits/_ but cant
  start with a digit.
• Reserved Words not allowed
• Java is case-sensitive (age ! Age)

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Primitive JavaDeclaration and Initialization of
Primitive Types

• Naming Conventions
• Typically, variables start with a lower case
  letter and new words start with an uppercase
  letter.
• minimumWage
• operatorTest
• Etc

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Primitive JavaBasic Operators

• Assignment
• , , -, , /
• Binary Arithmetic Operators
• ,-,,,
• Unary Operators
• -, , --
• Type Conversions

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Primitive JavaConditional Statements

• Relational and Equality Operators
• Equality Operators and !
• Relational Operators lt, lt, gt, gt

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Primitive JavaConditional Statements

• Logical Operators
• AND
• OR
• NOT !

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Primitive JavaIf Statement

• if (expression)
• statements
• Next statements
• if (expression)
• statements
• else
• more statements
• Next statements

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Primitive JavaWhile Statement

• while (expression)
• statements
• Next statements

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Primitive JavaFor Statement

• for (initialization test update)
• statements
• Next statements

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Primitive JavaDo Statement

• do
• statements
• while (expression)
• Next statements

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Primitive Javabreak

• outer
• while ()
• while ()
• if (disaster) break outer
• // Go to after outer labeled loop
• Statement where break would go if no outer
• //Control passes here after outer loop is exited.

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Primitive Javacontinue

• for (int i i lt 100 i)
• if (i10 0) continue
• System.out.println(i)

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Primitive Javaswitch

• The switch statement is used to select among
  several small integer (or character) values

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Primitive JavaConditional Operator ?

• Shorthand for simple if-else statements
• testExpr ? yesExpr noExppr
• Example
• minVal xlty ? x y

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Primitive Javamethods

• Function or Procedure
• Header
• Name
• Parameter List
• Return Type
• Overloading

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Primitive JavaConstants

• static
• final

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Reference TypesDefinition

• Any type that is not one of the 8 primitive types
  is a reference type. This includes
• Strings
• Arrays
• File Streams
• Classes you Create

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Reference TypesReference Variables

• Variable that stores the memory address where an
  object resides
• (see figure 2.1, p. 28)

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Reference TypesReference Variables

• Only operators allowed on references themselves
• Assignment
• Equality comparison or !
• Operations allowed on object being referenced
• Type conversion
• Access internal field or call method (dot
  operator)
• Use instanceof operator to verify stored object
  is of a certain type

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Reference TypesBasics

• dot operator (.)
• Used to select a method that is applied to an
  object
• Can access individual components of an object if
  they are viewable

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Reference TypesBasics

• Declaration of Objects
• Declaration simply provides a name for an object,
  not the actual object.
• Must construct the object using new
• Construction can specify an initial state for the
  object

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Reference TypesBasics

• Garbage Collection
• When a constructed object is no longer
  referenced by any variable, the memory it
  consumes is reclaimed and made available

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Reference TypesBasics

• Meaning of
• Stored values are copied
• lhs rhs
• lhs now refers to the same object as rhs.
  Objects are not copied this way. If you need to
  copy, use the clone method

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Reference TypesBasics

• Parameter Passing
• Call-by-value
• Figure 2.3

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Reference TypesBasics

• Meaning of
• lhs rhs if and only if they reference the same
  object. To compare the actual objects
  referenced, you need an equals method

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Reference TypesStrings

• Strings behave as reference types except that
  concatenation is allowed (using operators and
  )
• RULES
• Strings behave as objects except for the
  allowance of concatenation
• Strings are immutable

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Reference TypesStrings

• Concatenation
• this that //generates this that
• abc5 //generates abc5
• Comparison
• Use equals() and compareTo() methods
• Other methods
• length - compute string length
• charAt - get a single character
• substring get a substring

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Reference TypesStrings

• toString() converts primitive types and object to
  Strings

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Reference TypesArrays

• A basic mechanism for storing a collection of
  identically typed entities
• Each entity accessed via the array indexing
  operator
• Arrays always start at 0

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Reference TypesArrays

• Declaration
• int array1 new int 100
• //creates array of 100 ints
• int array2 3, 4, 5
• Try to get the size right the first time
  expanding arrays involves copying each individual
  value over a sometimes costly process

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Reference TypesArrayLists

• ArrayList is used for expanding arrays
• add method increases size by 1 and adds new item
  to array at appropriate position, expanding
  capacity if necessary
• Can only add objects no primitive types allowed!

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Reference TypesMultidimensional Arrays

• Arrays accessed by more than one index an array
  of arrays!

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Reference TypesException Handling

• Exceptions are used to handle exceptional
  occurrences such as errors. A try block
  encloses code that might generate an exception,
  and a catch block processes the exception. If
  things must be cleaned up before the exception is
  completed, the finally clause is used.

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Reference TypesException Handling finally
clause

• Three ways finally is used 1. The try block
  executes without exception control will pass to
  finally block. This will be true even if try
  block exits prior to the last statement via a
  return, break, or continue.

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Reference TypesException Handling finally
clause

• Three ways finally is used
• 2. An uncaught exception is encountered inside
  the try block control passes to the finally
  block. After executing the finally block, the
  exception propogates.

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Reference TypesException Handling finally
clause

• Three ways finally is used
• 3. If caught exception encountered in try block,
  control passes to appropriate catch block. After
  the catch block is executed, the finally block is
  executed.

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Reference TypesException Handling

• Common Exceptions
• Runtime exceptions
• Checked exceptions
• Errors

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Reference TypesRuntime Exceptions

• Do not have to be handled include events like
  divide-by-zero, illegal array access, etc. Do not
  have to be caught. Typically result in abnormal
  program termination.

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Reference TypesChecked Exceptions

• Must be handled programmer must include a catch
  block or a throws clause clause, allowing the
  exception to be passed back to a method that will
  handle it. Examples include end-of-file or
  file-not-found problems.

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Reference TypesErrors

• Errors are problems with the virtual machine.
  OutOfMemory or UnknownError are examples
  usually unrecoverable, should not be caught.

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Reference TypesThrow and Throws

• Throw clause used to throw an exception
• Throws clause indicates propogated exceptions

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Reference TypesI/O

• java.io package contains many methods to
  input/output information. Includes
• Stream operations
• System.in, System.out, System.err
• StringTokenizer
• FileReader

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Homework!!

• Due Tuesday, Sept. 5
• Assignment 2

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Objects and Classes

• Definition and creation
• Public / Private sections
• Specification vs. Implementation
• Constructors
• Accessors and Mutators
• toString
• equals
• Packages
• this
• instanceof Operator
• static class members
• Design Patterns

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Objects and ClassesDefinition and Creation

• An object is a data type that has structure and
  state.
• We view objects as atomic units the parts
  cannot be dissected by the general users of the
  object
• Information hiding makes implementation details,
  including components of an object, inaccessible
• Encaptulation is the grouping of data and the
  operations that apply to them to form an
  aggregate, while hiding the implementation of the
  agregate.

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Objects and ClassesDefinition and Creation

• Object oriented code supports reuse through
• Generic code
• Inheritance
• Polymorphism

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Objects and ClassesDefinition and Creation

• An object is an instance of a class, which
  consists of fields that store data and methods
  that are applied to instances of the class

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Objects and ClassesPublic vs Private

• Public members are visible to non-class routines
• Private members are not all data members should
  be private (in general)

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Objects and ClassesFields and Methods

• Field stores data
• Method performs an action

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Objects and ClassesClass Specification and
Javadoc

• Class specification represents what can be done
  to an object while the implementation represents
  how these specifications are met
• The javadoc program can be run to automatically
  generate documentation for classes in HTML format

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Objects and ClassesClass Specification and
Javadoc

• Comments that begin with / will be added to the
  documentation produced by the javadoc command
• Special tags include _at_author, _at_param, _at_return,
  _at_throws

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Objects and ClassesCommon Methods

• Constructors
• Accessors
• Mutators
• toString
• equals
• main

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Objects and ClassesCommon Methods

• Constructor
• Tells how an object is declared and initialized.
• Classes can have multiple constructors
• Default constructor initializes primitive fields
  to 0 and reference fields to null. (Exists only
  if there are no other constructors written)
• Constructors are methods with the same name as
  the class and no return type

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Objects and ClassesCommon Methods

• Mutators and Accessors
• Accessors examine data of the class, but do not
  change it.
• Mutators change the data of the class in a
  specified way.

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Objects and ClassesCommon Methods

• public String toString()
• Method that returns a string based on the objects
  state. Default returns the objects memory
  location unless creator of the class overrides it.

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Objects and ClassesCommon Methods

• public boolean equals(Object a)
• Method that tests to see if two objects hold the
  same value(s). The parameter to equals is an
  Object and must be checked to ensure it is an
  instanceOf the same class.

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Objects and ClassesCommon Methods

• public static void main
• Method called when java .class files are run.

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Objects and ClassesStatic Fields and Methods

• Static methods do not need a controlling object
  called by using the class name instead of an
  object name. Some fields are also static and if
  static is used with the keyword final, the field
  is a constant.

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Objects and Classesthis

• this is a reference to the current object can
  be used to send the current object, as a unit, to
  some other method
• Sometimes used to create default constructors
• public Date()
• this(1,1,2006)//call 3 parameter
  construtor

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Objects and ClassesinstanceOf

• Used to test if an expression is an instance of
  some class

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Objects and ClassesPackages

• Organizes a collection of classes
• The import directive is used to provide shorthand
  for a fully qualified class name
• The package statement indicates that a class is
  part of a package it precedes the class
  definition and the class is stored in a folder
  with that package name.

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Inheritance

• Definition
• Hierarchies
• Type compatibility
• Super and Final
• Overriding vs Overloading
• Abstract methods / Classes
• Multiple Inheritance
• Interface
• Generic Components