Primitive Types I

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Primitive Types I
Qi ZhangAug 27
COMP 110 Introduction to Programming
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Last Lecture

• Overview of
• Hardware software
• Programming language and compiler
• OOP basics
• A sample Java program

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Todays Lecture

• Review worksheet
• Need to turn in at the end of the class, only
  counted as attendance
• not graded
• In-class exercises writing algorithms
• Work in groups
• Think about the problem, discuss and write down
  your algorithm in pseudocode
• Present your answer
• Primitive types and expressions
• Assignment 1

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New Office Hours

• Time Mon 4-5PM, Thur 3-4PM
• If it still does not work for you, please make
  appointment

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Extra Credits for Class Participation

• Extra credits for answering questions in class
• Your answer has to be correct
• 1 question 1 pt
• Up to 5 pts
• Send me email after class and tell me
• Which question you have answered

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Review Work Sheet

• 5 minutes
• Open book
• Not graded
• Need to turn in at the end of the class, only
  counted as attendance

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In-class Exercises Writing Your Algorithm
Ped 1
Ped 2
Ped 3
Start
disk 1
disk 2
disk 3
End
Start
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In-class Exercises Writing Your Algorithm

• Work in 3-4 people groups
• Discuss
• Write down (pseudocode)
• Present
• 10 minutes

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In-class Exercises Writing Your Algorithm

• http//www.mazeworks.com/hanoi/

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Primitive Types and Expressions

• Become familiar with Java primitive types
  (numbers, characters, etc.)
• Learn about assignment statements and expressions

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Variables and Values

• Variables store data such as numbers and letters.
• Think of them as places to store data.
• They are implemented as memory locations.
• The data stored by a variable is called its
  value.
• The value is stored in the memory location.
• Its value can be changed.

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Declaring Variables

• Syntax
• Type Variable_1, Variable_2,
• Example int count,speed
• double interestRate
• A variables type determines what kinds of values
  it can hold (int,double,char, etc.).
• A variable must be declared before it is used.

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Types in Java

• A class type is used for a class of objects and
  has both data and methods.
• Have fun! is a value of class type String
• Scanner keyboard new Scanner(System.in)
• A primitive type is used for simple,
  nondecomposable values such as an individual
  number or individual character.
• int, double, and char are primitive types.

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Naming Conventions

• Class types begin with an uppercase letter (e.g.
  String).
• Primitive types begin with a lowercase letter
  (e.g. int).
• Variables of both class and primitive types begin
  with a lowercase letters (e.g. myName,
  myBalance).
• Multiword names are punctuated using uppercase
  letters.

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Java Identifiers

• An identifier is a name, such as the name of a
  variable.
• Identifiers may contain only
• letters
• digits (0 through 9)
• the underscore character (_)
• and the dollar sign symbol () which has a
  special meaning
• but the first character cannot be a digit.

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Java Identifiers, cont.

• identifiers may not contain any spaces, dots (.),
  asterisks (), or other characters
• 2moro netscape.com go-team (not allowed)
• Identifiers can be arbitrarily long.
• Since Java is case sensitive, stuff, Stuff, and
  STUFF are different identifiers.

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Keywords or Reserved Words

• Words such as if are called keywords or reserved
  words and have special, predefined meanings.
• Keywords cannot be used as identifiers.
• See Appendix 1 for a complete list of Java
  keywords.
• other keywords int, public, class

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Primitive Types
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Assignment Statements

• An assignment statement is used to assign a value
  to a variable.
• answer 42
• The equal sign is called the assignment
  operator.
• We say, The variable named answer is assigned a
  value of 42.
• examples
• amount 3.99
• firstInitial W
• score numberOfCards handicap
• eggsPerBasket eggsPerBasket - 2

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Assignment Compatibilities

• Java is said to be strongly typed.
• You cant, for example, assign a floating point
  value to a variable declared to store an integer.
• Sometimes conversions between numbers are
  possible.
• doubleVariable 7
• is possible even if doubleVariable is of type
  double.

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Assignment Compatibilities

• A value of one type can be assigned to a variable
  of any type further to the right
• byte -gt short -gt int -gt long -gt float -gt double
• (memory used)
• 1 2 4 8 4 8
• but not to a variable of any type further to
  the left.
• You can assign a value of type char to a variable
  of type int.

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Type Casting

• A type cast temporarily changes the value of a
  variable from the declared type to some other
  type.
• For example,
• double distance
• distance 9.0
• int points
• points (int)distance
• illegal without (int)

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Initializing Variables

• To protect against an uninitialized variable (and
  to keep the compiler happy), assign a value at
  the time the variable is declared.
• Examples
• int count 0
• char grade A

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Questions

• Which identifiers are legal?
• 7-11 seven-11 seven_11 seven.11 7.11
  7_11
• For the following variables,
• int myInt2
• double myDouble3.0
• which of the following statements are correct?
• myDoublemyInt // statement 1
• myIntmyDouble // statement 2
• myDouble(double)myInt //statement 3
• myInt(int)myDouble //statement 4