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# Lecture05 - Interactive Applications(CLI and Math...

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1 Interactive Applications (CLI) and Math Interactive Applications Command Line Interfaces The Math Class Example: Solving Quadratic Equations Example: Factoring the Solution Reading for this class: L&L, 3.5

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2 Interactive Applications (CLI) An interactive program with a command line interface contains a sequence of steps to: Prompt the user to enter input data Read and save the user’s responses Process the data after all input(s) are received We can prompt the user: System.out.println(“prompt text”); We can read and format user responses: type variable = scan.next Type ();
3 Interactive Applications (CLI) Similar to Quadratic.java (Page 129) int a, b, c; // integer coefficients Scanner scan = new Scanner(System.in); System.out.println(“Enter coefficient A”); a = scan.nextInt(); System.out.println(“Enter coefficient B”); b = scan.nextInt(); System.out.println(“Enter coefficient C”); c = scan.nextInt(); // we have the data to solve the equation // ax-squared + bx + c = 0 for it’s roots

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4 We have the input values, now what? To solve the quadratic equation, we need to program in Java the formulas learned in high school algebra: discriminant = b squared – 4ac root1 = (-b + squareroot of discriminant)/2a root2 = (-b - squareroot of discriminant)/2a How do we program those equations? We need to use the Math Class Library, Expression Evaluation, and Assignment
5 The Math Class The Math class is part of the java.lang package The Math class contains methods that perform various mathematical functions These include: absolute value square root exponentiation trigonometric functions

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6 The Math Class The methods of the Math class are static methods (also called class methods ) Static methods can be invoked through the class name – no object of the Math class is needed value = Math.cos(90) + Math.sqrt(delta); Similar to Quadratic.java (page 129) discriminant = Math.pow(b, 2) – 4.0 * a * c; root1 = (-1.0 * b + Math.sqrt(discriminant))/(2.0 * a); root2 = (-1.0 * b – Math.sqrt(discriminant))/(2.0 * a); Note: We can’t program the + in the formula on page 130 in Java. We need to calculate each root separately
7 Solving Quadratic Equations However, the textbook’s program to solve for the roots of a quadratic equation is deficient!

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