Class 7

Objectives Identify, declare, and use primitive data types Use variables in programs to hold data in RAM Use assignment statements to store data with proper identifiers Use operators and parentheses correctly in numeric expressions

Introduction Data are collections of raw facts or figures A program performs operations on input data to output information Input data can come from a variety of sources The program itself Users of the program External files

Variables Variables are like storage locations in the computer’s memory. Storage for the value of the variable

Naming Rules of Variables First character must be one of the letters a-z, A-Z, or an underscore ( _ ) or a $ After first character use a-z, A-Z, 0-9, underscore ( _ ) or $ Any length Keep them meaningful

Variable Rules (con’t) Case sensitive ItemsOrder does not equal itemsorder Cannot declare two variables of the same name in a method Cannot give a variable the same name as a method

Storing Data Java is a strongly typed language Variables must be declared with a data type Variable locations can hold only that data type Java has two categories of data types Primitive data types hold single data items Integers, characters, floating point, and booleans are primitive types Reference data types hold a value that refers to the location of the data All Objects and arrays are reference types

Intrinsic Data Types JAVA has eight intrinsic data types, which form the basis for all other data types (i.e., classes): 1. boolean: - a 1 byte value that is assigned a value of either true or false (both are JAVA defined values). Boolean values have no direct conversion to integer values, and are initialized to false.

Intrinsic Data Types 2. byte: - a 1 byte integer, capable of representing numbers from numbers from -128 to +127. It is initialized to 0. 3. char: - a 2 byte integer that is normally used to represent character values using the Unicode system (the first 128 values of which correspond to ASCII values). It is initialized to \u0000.

Intrinsic Data Types 4. short: - a 2 byte integer, able to represent numbers between -32K and +32K. It is initialized to 0. 5. int: - a 4 byte integer, able to represent numbers between -2 billion and +2 billion.

Intrinsic Data Types 6. long: - an 8 byte integer, capable of representing numbers between -2 and +2 . It is initialized to 0. 7. float: - a 4 byte IEEE format real number, giving about 7 decimal digits of precision. It is initialized to 0.0f. 63 63

Intrinsic Data Types 8. double: - an 8 byte IEEE format real number, giving about 15 decimal digits of precision. It is initialized to 0.0d.

Declaring Variables General form: 1. dataType identifier; 2. dataType identifier, identifier, identifier; 3. dataType identifier = initialValue; 4. dataType identifier = new dataType(); int myAge; int myAge, yourAge, theirAges; int myAge = 24; Person me = new Person();

Key JAVA Operators ( ) Parenthesis (X+2)/3 Operator Description Example ( ) Parenthesis (X+2)/3

Key JAVA Operators Operator Description Example * Multiply X*2

Key JAVA Operators Operator Description Example / Divide X/12

Key JAVA Operators Operator Description Example % Modulus 7%3

Key JAVA Operators Operator Description Example + Add X+7

Key JAVA Operators Operator Description Example - Subtract X-6

Key JAVA Operators = Assignment operator Y=X+3 Operator Description Example = Assignment operator Y=X+3

Arithmetic Operators The order of operator precedence is a predetermined order that defines the sequence in which operators are evaluated in an expression Addition, subtraction, multiplication, and division can manipulate any numeric data type When Java performs math on mixed data types, the result is always the larger data type Casts allow programmers to force a conversion from one primitive type to another

Numeric Expressions Numeric expressions evaluate to a number Only numeric primitive data types may be used in a numeric expression A value and variable must be separated by an arithmetic operator Unless parentheses supercede, an expression is evaluated left to right with the following rules of precedence: Multiplication and/or division Integer division Modular division Addition and/or subtraction

Parentheses in Expressions Parentheses may be used to change the order of operations The part of the expression within the parentheses is evaluated first Parentheses can provide clarity in complex expressions Numeric and conditional expressions should be grouped with parentheses Parentheses can be nested Java evaluates the innermost expression first and then moves on to the outermost expression

How precedence works x = ( 3 + 8 ) / 3 * 2 + 5 % 3 x = ? 11 / 3 / 3 * 2 + 5 % 3 x = 3 * 2 + 5 % 3 x = 6 + 5 % 3 x = 6 + 2 x = 8

Assignment Statements General syntax: identifier = value; x = 5; dataType identifier = value; int x = 6; identifier = formula; x = 3 * y+5; identifier = differentIdentifier; x = y;

Using Variables in Output to the console instead of to a window System.out.println(“Hello World”); System.out.println(5); System.out.print(“my age is \n“ + age); System.out.println(“ “); String concatenation operator

Assignment Statements Exercise 1 The value in number is number _ Assignment Statements Exercise 1 int number; number = 5; System.out.println(“The value in number is ” + “number”) ; number ? 5

Assignment Statements Exercise 2 The value in number is 5 _ Assignment Statements Exercise 2 int number; number = 5; System.out.println(“The value in number is ” + number) ; number ? 5

Multiple Assignment Statements Tracing Code: exercise 3 int Checking; int Miles; long Days; Checking = -20; Miles = 4276; Days = 187000; Days ? 187000 Checking ? Miles ? -20 4276

System.out.println( “We have made a” + “ long trip of ” + Miles + “ miles.”); System.out.print(“Our checking account” + “ balance is ” + “Checking”); System.out.print(“\nExactly ” + Days + “ days ago Columbus” + “ stood on this spot.”); Days 187000 Checking -20 Miles 4276

Multiple Assignment Statements Tracing Code: Exercise 4 double RegWages, BasePay = 18.25; double RegHours = 40.0; double OTWages, OTPay = 27.78; double OTHours = 10; double TotalWages; RegWages ?.? OTWages ?.? TotalWages ?.? BasePay 18.25 OTPay 27.78 RegHours 40.0 OTHours 10

Basic usage of operators RegWages = BasePay * RegHours; OTWages = OTPay * OTHours; TotalWages = RegWages + OTWages; System.out.println( “Wages for this” + “ week are $ ” + TotalWages ); RegWages ?.? OTWages ?.? 730.0 277.8 TotalWages ?.? BasePay 18.25 OTPay 27.78 RegHours 40.0 OTHours 10 1007.8 PG 66 ~ Pgrm. 2-20

Write assignment statements A) Adds 2 to A and stores the result in B. B = A + 2; pg. 85 Problem #20a a) Adds 2 to A and stores the result in B b) Multiplies B by 4 and stores the reul in At

Write assignment statements B) Multiplies B times 4 and stores the result in A. A = B * 4;

Write assignment statements C) Divides A by 3.14 and stores the result in B. B = A / 3.14;

Write assignment statements D) Subtracts 8 from B and stores the result in A. A = B - 8;

Write assignment statements E) Stores the value 27 in A. A = 27;

What is this program’s output int Freeze = 32, Boil = 212; Freeze = 0; Boil = 100; System.out.print(Freeze + “\n “ + Boil + “\n”); 100 _

What is this program’s output int X = 0, Y = 2; X = Y * 4; System.out.println( “” + X + “\n “ +Y ); 8 2 _

System.out.print(“I am the incredible” + “ computing\nmachine ” + “\nand I will\namaze\n” + “you.”);

I am the incredible computing machine and I will amaze you. _

What is this program’s output System.out.println( “Be careful\n” + “This might/n be a trick ” + “question”); Be careful This might/n be a trick question _

What is this program’s output int A, X = 23; A = X % 2; System.out.println( X); System.out.println( A ); 23 1 _

Conclusion of Class 7