6.092-1 Types, variables, operators (Java Programming)

6.092: Introduction to Java 1: Types, Variables, OperatorsGoal Learn enough Java to do somethinguseful Examples: • Simulate a natural/engineering process• Manipulate PDFs • Draw pretty graphics Assignments • View and submit via Stellar • Due at 3 PM the next day (24 hours) • Collaborate with others • Write your own code • Must submit first assignment Must submit a “reasonable” attempt for 6/7assignments to pass The ComputerCentral Processing Unit (CPU) Input/Output (IO) Devices Memory CPU Instructions z = x + y Read location x Read location y Add Write to location z Programming Languages • Easier to understand than CPU instructions • Needs to be translated for the CPU to understand it Java • “Most popular” language • Runs on a “virtual machine” (JVM) • More complex than some (eg. Python)• Simpler than others (eg. C++) Compiling JavaSource Code (.java) Byte Code (.class)javac java First Program class Hello { public static void main(String[] arguments){ //Program execution begins here System.out.println("Hello world."); } } Program Structure class CLASSNAME { public static void main(String[] arguments){ STATEMENTS } } OutputSystem.out.println(some String) outputs tothe console Example: System.out.println(“output”); Second Program class Hello2 { public static void main(String[] arguments){ System.out.println("Hello world."); //Print once System.out.println("Line number 2"); //Again! } } Types Kinds of values that can be stored and manipulated. boolean: Truth value (true or false).int: Integer (0, 1, -47).double: Real number (3.14, 1.0, -2.1).String: Text (“hello”, “example”).Variables Named location that stores a value of one particular type. Form: TYPE NAME; Example: String foo; Assignment Use = to give variables a value.Example: String foo; foo = “IAP 6.092”; Assignment Can be combined with a variable declaration. Example: double badPi = 3.14; boolean isJanuary = true; class Hello3 { public static void main(String[] arguments){ String foo = "IAP 6.092"; System.out.println(foo); foo = "Something else"; System.out.println(foo); } } Operators Symbols that perform simple computationsAssignment: = Addition: + Subtraction: -Multiplication: * Division: /Order of Operations Follows standard math rules: 1. Parentheses 2. Multiplication and division 3. Addition and subtraction class DoMath { public static void main(String[] arguments){ double score = 1.0 + 2.0 * 3.0; System.out.println(score); score = score /2.0; System.out.println(score); } } class DoMath2 { public static void main(String[] arguments){ double score = 1.0 + 2.0 * 3.0; System.out.println(score); double copy = score; copy = copy /2.0; System.out.println(copy); System.out.println(score); } } String Concatenation (+) String text = "hello" + " world"; text = text + " number " + 5; //text = "hello world number 5" Assignment: GravityCalculatorCompute the position of a falling object: x(t) = 0.5 × at2 + vit + xi MIT OpenCourseWarehttp://ocw.mit.edu 6.092 Introduction to Programming in Java January (IAP) 2010 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms.