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Java

Java. Variables, Types, and Math Getting Started Complete and Turn in Address/Poem. Learning Objectives. Understand how to declare and use primitives variables. Be able to read a simple Java program. Be able to incorporate math expressions into a Java program

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Java

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  1. Java Variables, Types, and Math Getting Started Complete and Turn in Address/Poem

  2. Learning Objectives • Understand how to declare and use primitives variables. • Be able to read a simple Java program. • Be able to incorporate math expressions into a Java program • Be able to find and use JavaDocs

  3. Review • // • public static void main (String [] args) • { • System.out.println(“Hello world”); • System.out.print(“Hello world”); • int num; • num = 30; • double num2; • num = input.nextInt(); • double num2 = input.nextDouble(); • System.out.printf( “The second number is %5.2f\n", num2 ); • }

  4. Primitive Types (Not objects) • byte • short • int (4 bytes) -2,147,483,648 to 2,1147,483,647 • long +/-9,223,372,036,854,775,808 • float • double (8 bytes) 10 e +/-308 with 15 significant digits • char • boolean true or false

  5. The variables exist while main is running. public class Interest { public static void main(String[] args) { /* Declare the variables. */ double principal=0; // The value of the investment. double rate, interest; // The annual interest rate. // Interest earned in one year. /* Do the computations. */ principal = 17000; rate = 0.07; interest = principal * rate; // Compute the interest. principal = principal + interest; // Compute value of investment after one year, with interest. // (Note: The new value replaces the old value of principal.) /* Output the results. */ System.out.print("The interest earned is $"); System.out.println(interest); // Can also use //System.out.print("The interest earned is $“ + interest); System.out.print("The value of the investment after one year is $"); System.out.println(principal); } // end of main() } // end of class Interest

  6. Sort of primitive type, but it’s an object • String A sequence of characters. • The type declarations does start with an uppercase letter.

  7. Variables in Programs • Declare the variables inside the main subroutine. (For now) • You can also declare variables where you need them. (Declare a looping variable at the loop) • int numberOfStudents; • String name; • double x,y; • boolean isFinished;

  8. Simple input and math import java.util.Scanner; // program uses class Scanner publicclass Addition { // main method begins execution of Java application publicstaticvoid main( String args[] ) { // create Scanner to obtain input from command window Scanner input = new Scanner( System.in ); int number1; // first number to add int number2, sum; // second number to add String name; System.out.print( "Enter first integer: " ); // prompt number1 = input.nextInt(); // read first number from user System.out.print( "Enter second integer: " ); // prompt number2 = input.nextInt(); // read second number from user System.out.print("Enter your name "); name = input.nextLine(); sum = number1 + number2; // add numbers System.out.printf( "Sum is %d\n", sum ); // display sum System.out.println("Thanks " + name);// Note: Uses the + for concatenating } // end method main } // end class Addition Use input.nextDouble(); for getting a double value

  9. // Addition.java// Addition program that displays the sum of two numbers. • Displays the file name and a brief description of the program

  10. import java.util.Scanner; • Import declaration • This is a predefined class this program will use • Package: A collection of classes. • Java Class Library or Java Application Programming Interface (API): Collection of Packages • This will use the Scanner class from the java.util package • Note: All import declarations MUST appear before the first class declaration in the file. Placing an import declaration inside a class declaration’s body or after a class declaration is a syntax error. • Note: “cannot resolve symbol” error->Forgetting to include an import declaration for a class used in your program.

  11. public class Addition • Begins the declaration of the Addition class. • The file name must be Addition.java (case sensitive)

  12. Scanner input = new Scanner( System.in ); • Variable declaration • Declares the variable (object) input is of type Scanner. • Scanner enables the program to read data (numbers) for use in the program. • = Declares that the Scanner variable input should be initialized in its declaration with the result of the expression newScanner(System.in) to the right side of the =. • Creates a Scanner Object that can be used to read data entered through the keyboard.

  13. int number1; // first number to add int number2; // second number to add int sum; // sum of number1 and number2 • Declares three integer variables. • -2,147,483,648 to 2, 147, 483, 647 • Other types • float like real numbers • char: characters • Primitive or built in types • Variables follow identifier rules • Start the variables with a lowercase letter. (Style)

  14. System.out.print( "Enter first integer: " ); • The prompt for user input • Need to include a prompt for every value input

  15. number1 = input.nextInt(); • Uses the Scanner object input.nextInt() method to obtain an integer from the user at the keyboard. At this point the program waits for the user to type the number and press enter. • This line is read “number1 is assigned the value of input.nextInt().”

  16. Other common Scanner Methods for input • Entering an Integer • integerVariable = input.nextInt(); • Entering a double • doubleNumber = input.nextDouble(); • Entering a String. Reads the entire line. • stringVariable = input.nextLine(); • Entering a String. Reads until it gets to a space • stringVariable = input.next();

  17. sum = number1 + number2; • Calculates the sum of number1 and number2 and places the result in the integer variable sum.

  18. System.out.printf( "Sum is %d\n", sum ); • Displays the sum. • Could also use • System.out.printf( "Sum is %d\n", number1+number2 ); • Or • System.out.println(“Sum is “ + sum); • But this will give a result you might not expect. • System.out.println(“Sum is “ + number1 + number2);

  19. Simple Integer Math Operations () • * Multiply • / Integer Division • % MOD, The remainder of integer division. • +, - • Order of Operation • () • *, /, % • +, -

  20. Evaluate the following • 5/2 • 24 / 15 • 15 / 24 • 5 % 2 • 24 % 15 • 17 % 12 • 140 / 25 • 140 % 25

  21. Show javadocs • On the left lists the different classes. • Use the button on the class website to get to Javadocs • Find the Math class and look up the following methods. • PI • sqrt • pow • To use these in a program you need to use the form • ClassName.methodName(arguments if any) • Math.method(arguments)

  22. Examples • ans = Math.sqrt(9); • ans = Math.sqrt(16); • ans = Math.pow(3); • ans = Math.sqrt(Math.pow(3,2) + Math.pow(2,2));

  23. Translate to Java

  24. Dry Run the Following publicclass DryRun9_15_09 { publicstaticvoid main(String[] args) { int a, b, c = 20; double d = 1.0; a = c + 10; b = a + c; System.out.println("Numbers " + a +" " + b + " " + c); System.out.println(a+b+c); c = a % 7; b = a / 7; a = a + 2*b + c % 3; System.out.println("Numbers " + a +" " + b + " " + c); System.out.println(a+b+c); d = 1.0/3; System.out.println(d); System.out.printf("%5.2f \n", d); d = Math.sqrt(a-b); System.out.println(d); System.out.printf("%5.2f \n", d); } }

  25. First Input Programs • Mile to inch: YourNameMileToInch • Input: The number of miles traveled • Output: The equivalent distance converted to inches • 5280 feet per mile, 12 inches per foot • Change: YourNameChange • Input: The amount of change in pennies • Output: The least amount of coins it takes to make the change. • Example: Input: 66 cents • Output: • To get 66 cents you need: • 2 Quarters • 1 Dime(s) • 1 Nickel(s) • 1 Cent(s)

  26. Second Input Program Complete additional programs as pushes. • Complete one of the following • Quadratic formula • Input: a, b and c (of type double) • Output: The positive root (-b + sqrt(b2 – 4ac))/(2a) • Distance formula • Input: The x and y coordinates for two points • Output the distance between the points: • Distance = sqrt((y1-y2)2 + (x1-x2)2) • Push: Calculate the distance between two points that are on a 3-D grid. That is they have an x, y, and z value. • Given the lengths of three sides of a triangle, find the area of the triangle. • Find a way to calculate this even if it is not a right triangle. (Do a little research)

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