CS 177 Recitation

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CS 177 Recitation

• November 2, 2006

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Announcements

• Project 3 due next Wednesday
• Exam 2 will come back next week

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Objects

• What is an object?
• Something which has data and operations
• Could an integer be considered an object?
• Yes.
• What are its data and operations?
• Data ? integer number
• Operations ? , -, /, , gt, lt, ,

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Objects

• Think of a car as an object.
• What are its data?
• Color, model, year, horsepower, mileage, etc
• What are its operations?
• Start engine, steer, accelerate, brake, change
  gears, etc
• How about the data for a string?
• The sequence of characters that are enclosed in
  quotes
• How about the operations for a string?
• Convert to uppercase, lowercase, access a
  particular character, search for a substring,
  find first occurrence of a character

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Object Oriented Programming

• What is object-oriented programming?
• A programming approach in which the problem is
  broken down into objects
• Example A classroom simulator could have objects
  for the teacher and students, desks, projector,
  chalkboard, etc
• What makes object-oriented programming so useful?
• Large systems can be broken into objects, and the
  objects can be implemented by different teams and
  later brought together
• Objects can be reused in other applications
• Why is an object an abstract representation?
• It does not represent all possible data and
  operations
• Example A car object would not represent the
  week-old french fry on the floor of the back seat
• We only represent what is necessary to solve the
  problem

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Properties and Methods

• What are properties of objects?
• The data or characteristics of an object
• Example For a string object, the length is a
  property
• str Strings rock!
• str.length would give us 13
• What are methods of objects?
• The operations that can be performed on the
  object
• str MaKe Me LOwEr
• lowstr str.toLowerCase()
• lowstr is now make me lower
• None of the methods for strings actually modify
  the string, they simply return a new string

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Properties and Methods

• What are some properties that we already know?
• document.myForm.myInput.value
• document.images.myImage.src
• What is a method that we know?
• document.write()
• In the above examples, what is the object?
• document
• So how can we access properties or methods?
• ltObject namegt.ltProperty or Method namegt

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String Manipulations
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Example 1
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More String Manipulations

• What does the charAt() method do?
• Given an integer, it returns the character at
  that index in the string
• str Clark Kent
• ch str.charAt(3) (ch now holds r)
• ch str.charAt(5) (ch now holds )
• Note The first character is at index 0, and the
  last is at n-1.
• What does the substring() method do?
• Given a beginning index and an ending index, it
  returns the part of the total string from the
  beginning index up to, but not including, the
  ending index.
• str My TA is AWESOME!
• sub str.substring(9,16) (sub now holds
  AWESOME)
• sub str.substring(4,12) (sub now holds A is
  AWE)
• Note First index is included in the substring,
  but the last is not.

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Example 2

• Using charAt() and substring(), write a function
  Capitalize(str) that receives a string and
  returns the same string with the first letter
  capitalized and all others lowercase.

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More string methods

• What does the search() method do?
• Given either a string or list of characters, it
  returns the index of the beginning of the first
  occurrence of the string or any character
  specified in the list.
• str I think therefore I am
• i str.search(I)
• (i 0)
• i str.search(f)
• (i 13)
• i str.search(here)
• (i 9)
• i str.search(\klmn\)
• (i 5)
• i str.search(\the\)
• (i 2)

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General searching
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Example 3

• Write JavaScript code which removes the all
  characters a from the string str
• str banana
• result
• i 0
• while(i lt str.length)
• if (str.charAt(i) ! a)
• result result str.charAt(i)
• i i 1
• str result
• What would result be here?
• bnn

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Example 4

• Write JavaScript code to look through the string
  str and find the index of the first occurrence of
  help, but is not case-sensitive (i.e. it would
  also find HeLP).
• str IsohHeLpelPmonhEllpious
• str str.toLowerCase()
• index str.search(help)
• What would index be here?
• 4

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Questions?