600'107 Introduction to Programming in Java

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600.107Introduction to Programming in Java

• Review Session
• Jai Madhok
• Email jaimadhok_at_jhu.edu

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Key Concepts

• Identifiers- What are they?
• Rules to determine invalid Vs valid identifiers
• Cannot be a reserved word
• No spaces in between
• No Symbols other than the and _
• Cannot begin with a digit

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Data Types

• 3 kinds of primitive data types
• Type conversion between data types
• Implicit Vs Explicit type conversion
• The Cast operator
• Syntax (dataType) Expression
• What happens when an operator has mixed operands?

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Strings

• It is an Object
• In Java, they are enclosed in double quotes
• What is a null string? Empty string?
• How does indexing work?
• Predefined Methods
• substring(startIndex, stopIndex)
• charAt(index)
• indexOf(ch)
• concat()
• length()
• replace()
• toLowerCase()/toUpperCase()

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Named Constants

• Use the word final
• Identifier is in all Capital Letters
• Memory location whose content is not allowed to
  change during program execution
• Ex final int CENTS_PER_DOLLAR100
• Several Advantages
• Prevent typographical errors
• Easy to modify the program in the future
• If you mistype the name of the location computer
  will warn you as compared to typing in a wrong
  value which the computer will blindly accept
• Good programming practice

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Input Statements

• To put data into variables from an input device
  we first create an input stream object and
  associate it with a standard input device
• Scanner scan new Scanner (System.in)
• More about Scanner
• next()
• nextInt()
• nextDouble()
• nextLine()
• How do we read in a single character using a
  scanner object?

Know how to use these!
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Tokenizing Parsing

• Sometimes we read in input in the form of a
  string and then want to extract numeric data from
  it
• How do we do this? Tokenize and Parse
• Syntax
• StringTokenizer t new StringTokenizer(str,
  delimiters)
• Say we want an integer
• int a Integer.parseInt(t.nextToken())
• Other method Double.parseDouble()
• Note Parsing and type casting are different
  things

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File Handling

• A file is defined as an area in secondary storage
  used to hold information
• Scanner scanf new Scanner(new FileReader(filename
  1))
• PrintWriter oFile new PrintWriter(filename2)
• Warning Closing the file you are writing to is
  more important than you think it is
• Use same methods for reading and
  writing/formatting files as you have been for
  user input/monitor display

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Formatting output with printf

• Syntax
• System.out.printf(formatString, argumentList)
• formatString is a string specifying the format
• argumentList list of arguments containing
  constant values, variables, expressions separated
  by commas
• --------------------------------------------------
  -----------------------------------
• Example
• System.out.printf(There are .2f inches in d
  centimeters n ,cm/2.54, cm)
• Where cm is a variable of the type int.
• Note You can also use the DecimalFormat class
  to format your decimal output. Take your pick!

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More fun with strings

• compareTo
• Compare Strings character by character until a
  mismatch is found.
• What does this method return?
• What is the basis for deciding what a mismatch
  is and what it isnt?
• equals
• Case sensitive method
• How to solve the case sensitivity issue?
• What does the method return?

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Operators- Order of Precedence

• () .
• Unary Operators negation, casting, not (!),
  , --
• Arithmetic Operators I /
• Arithmetic Operators II -
• Comparison Operators lt lt gt gt
• Equivalence Operators !
• Logical AND
• Logical OR
• Ternary Operator ?
• Assignment Operators , , -, , /,

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Control Structures

• Provide alternatives to sequential program
  execution and are used to alter flow of execution
• Alternatives are
• (i) Selection if, if/else, switch/case
• (ii) Repitition for, while, do-while

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While loops

• Using loop control variables
• Counter controlled while loops
• Sentinel Controlled while loops
• Flag controlled while loops
• EOF controlled while loops
• Do-While Loops ? different
• from a generic while

T
F
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For loops

• for (initial statement loop condition update
  Statement)
• KNOW THIS LOOP COLD!

Initial Statement
Loop Condition
T
Statements
Update Statement
F
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Break Statement

• Exit early from a loop
• Skip the remaining cases in a switch case
  construct
• Dont try and use them at random places to make
  your code work, most of the time it wont.

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Packages in Java

• util Scanner, StringTokenizer
• io- BufferedReader, FileReader
• text- DecimalFormat
• lang String, Math

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Miscellaneous things

• Reading flow in java
• a a 2
• A in ASCII is 65
• ASCII is a subset of Unicode
• Escape Sequences
• Compound Operators
• Increment/Decrement operators, pre/post

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Documentation Reading

• Read up some common methods of the following
  classes for use in the assignments and exams.
• String
• Scanner
• StringTokenizer
• Math
• Character

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Exam Format

• True/False
• Multiple Choice
• Code Tracing
• Code Completion
• Finding Errors
• Other random kinds of questions like matching
  exercises are a possibility

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Exam Tips

• Read through all questions carefully
• Write answers legibly, because we have to be able
  to read them to grade them
• Show all work for partial credit
• Do not spend too much time on any one particular
  problem if it is causing trouble, come back to it
  later on
• Read through the chapter summaries in the text
  book and all of Dr.Hs class notes
• Good Luck!

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Questions

• ?

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Sample Code Tracing 1

• char let A
• for (int i1 ilt3i)
• for(int jIjlt5j)
• System.out.print(let)
• System.out.println()
• let1
• Predict the output? 6 points
  Difficulty Medium

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Sample Code Tracing 2

• n1 6 n210
• if(n1 gt n2/2)
• if(true false)
• System.out.print( one )
• else
• System.out.print(two )
• System.out.print(three )
• Predict the output? 3 points Difficulty Easy

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Sample Code Tracing 3

• int num6
• while(numlt16)
• switch(num4)
• case 1 System.out.println(one) break
• case 2 System.out.println(two)
• case 3 System.out.println(three)break
• case 0 System.out.println(multiple)
• num3
• 4-6 points Difficulty Medium

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Sample Code Tracing 4

• boolean atrue, bfalse
• if (a (true !b) )
• if( b (!a false) )
• System.out.println(happy)
• else System.out.println( halloween )
• System.out.println(goblins)
• 6 points Difficulty Medium