Question

So in my java class we have a homework assignment to use System.currentTimeMillis to display the amount of time between clicks. I’ve tried and tried but it isn’t working. Here’s my code.

 1 /* Matthew Caldwell
 2  * September 21, 2011
 3  * Homework #4: Problem 5.8.1 pg. 149
 4  * Program that displays the amount of time that passed
 5  * between two mouse clicks. Nothing is displayed
 6  * on the first click, then each successive click will 
 7  * display how much time passed between that click and 
 8  * the previous one. 
 9  */  
10  
11 import objectdraw.*; 
12 import java.awt.*; 
13  
14 public class ElapsedTimeClient extends WindowController { 
15    
16   public static void main(String[]args) { 
17     new ElapsedTimeClient().startController(800,500);
18   }
19 
20   private Text title,result;
21   private double count = 0;
22 
23   public void begin() {
24     
25     // Set up the title and result
26     title = new Text("CLICK COUNTER",
27                      canvas.getWidth() / 2,
28                      20, canvas);29     title.move(-title.getWidth() / 2, 0);
30     result = new Text("", canvas.getWidth() / 2, 40, canvas);
31 
32   }
33 
34   public void onMouseClick(Location p) {
35 
36     double timerS=0;
37 
38     if(count == 0) {
39       timerS = System.currentTimeMillis();
40     } else {
41       result.setText("The time between clicks was " +
42                      (System.currentTimeMillis() - timerS)/1000 +
43                      " seconds.");
44       timerS = System.currentTimeMillis();
45     }
46 
47     count++;
48 
49   } 
50  
51 }

I don’t really want anyone to completely tell me how to do it but I just need a little guidance. What am I doing to make this wrong?
The code all compiles and runs just fine but when I click instead of giving me the time that elapsed between clicks it’s giving me a big long number that never changes. It’s telling me 1.316639174817E9 almost every single time.

Answer 1

Firstly, system time in millis should be represented as a long, not a double.

Secondly, you need to make the variable that holds the time since the last click (timerS) an instance variable, it’s currently method local and so reset every time.

In short, change:

double timerS=0;

from being a local variable, to an instance variable, and a long:

public class ElapsedTimeClient extends WindowController { 
long timerS;