7/31: Math.random, more methods About DrawLine.java modifications –allow user input –draw a curve Method definitions Math.random()

Allow User Input (1 of 2) Add in an init method for two input dialog boxes. double coeff;//note that I declared these double yInt; //two variables as global. public void init () { cText = JOptionPane.showInputDialog (“Coefficient, please.”); yText = JOptionPane.showInputDialog (“Y-intercept, please.”); coeff = Double.parseDouble ( cText ); yInt = Double.parseDouble ( yText ); }

Allow User Input (2 of 2) Use coeff & yInt in the drawDot method int drawDot ( int a ) { int b; //must cast to int below b = (int) (coeff * a + yInt) ; return b; }

Draw a Curve Change the formula in the drawDot method from: int drawDot ( int a ) { int b; b = 2 * a + 10 ; return b; } to: int drawDot ( int a ) { int b; b = 2 * ( a * a ) + 10 ; return b; }

Method Definitions in SquareInt.java (simple version below), we see a method called square: public void paint ( Graphics g ) { g.drawString(square(x) + “ “,25,25); } public int square ( int y ) { return y * y ; }

Method Definitions public void paint ( Graphics g ) { g.drawString(square(x) + “ “,25,25); } public int square ( int y ) { return y * y ; } the method square is called in this line. Because it is in parentheses, x is the value to use as the input.

Method Definitions public void paint ( Graphics g ) { g.drawString(square(x) + “ “,25,25); } public int square ( int y ) { return y * y ; } x fits the requirement that it must be an integer.

Method Definitions public void paint ( Graphics g ) { g.drawString(square(x) + “ “,25,25); } public int square ( int y ) { return y * y ; } using x as the input, the method calculates a return value.

Method Definitions public void paint ( Graphics g ) { g.drawString(square(x) + “ “,25,25); } public int square ( int y ) { return y * y ; } the returned value is what replaces the square(x). This value is of type int. x * x

Example: Maximum.java (p. 212) public void init () { (stuff left out…) double max = maximum ( num1, num2, num3 ); outputArea.setText ( “Max is “ + max ); } public double maximum ( double x, double y, double z ) { return Math.max ( x, Math.max ( y, z ) ); }

Important: Coercion of Arguments Java will automatically promote variables to larger types when necessary; EX: int to double. In Math.pow, the requested types of input are double. However, Java will create a double version of an int variable to use in that method automatically. go to Java class index for Math. pow Math. pow read p carefully

Math.random() generates a random double number in the range 0.0 <= x < 1.0 To utilize this function, we use scaling & shifting. scaling: multiplying the function by a number to get the range we want. shifting: adding a number to the function to get the beginning point of the range that we want.

Math.random() EX: Math.random () shift it by 1: Math.random() + 1 makes 1 to <2 scale it by 6: Math.random()* 6 makes 0 to <5 to simulate rolling a die, we want 6 possibilities (or a range of 6), from 1 to 6. They have to be integers. (int) ( Math.random() * );

Program of the day pg. 220 RollDie.java Modify the program to allow the user to input how many times to roll the die.