Question

I’m new to Java programming, I am programming Java 1.6 with Android.

I have a simple function that makes a number go up and down between 0 and 200. I would like to put this into a Sine function but keep getting errors with what I’ve been trying.

I want my program to update an int (Number1) via a sine wave y axis.

Any ideas change the following logic into a Sine function? (disregard the 2nd number)

code:

private int Number1 = 150;
private int Number2 = 0;
private int counter = 0;     

  public void updateNumbers() {   
            if (counter == 0) {
                if (Number1 < 200) {
                    Number1 = Number1 + 50;
                    Number2 = Number2 - 50;
                    if (Number1 >= 200) {
                        counter = 1;
                    }
                }               
            } else if (counter == 1) {
                if (Number2 < 200) {                                       
                    Number1 = Number1 - 50;
                    Number2 = Number2 + 50;               
                    if (Number2 >= 200) {
                        counter = 0;
                    }
                }
            }
        }           

Answer 1

Okay, so what you want to do is build a sine wave that goes between 0 and 200, but with what period? Did you want it to loop about every 8 calls?

How about this, leveraging the built-in Java Math.sin function:

private static final double PERIOD = 8; // loop every 8 calls to updateNumber
private static final double SCALE = 200; // go between 0 and this

private int _pos = 0;
private int Number1 = 0;

public void updateNumber() {
    _pos++;
    Number1 = (int)(Math.sin(_pos*2*Math.PI/PERIOD)*(SCALE/2) + (SCALE/2));
}

Basically, we keep a variable that counts how many updates we’ve done, and scale that to match the period of a sine wave, 2*PI. That acts as the input to the ‘real’ sin function, giving us something that goes between -1 and 1 but has the right frequency. Then, to actually set the number, we just scale that to be between -100 and 100 and then add 100 to move it to be in the 0-200 range you wanted from the beginning.

(You don’t have to cast the number to an int if a double works for you, I was just keeping with the spirit of what you wrote above.)