Java timer class does not auto refresh a Runtime function?

Question

I have this timer function written in java.

    import java.util.Timer;  //Libraries used
    import java.util.TimerTask;

    public static void main(String[] args) {
    Timer clock = new Timer();
    clock.schedule(new TimerTask() {
          @Override
          public void run() {
              System.out.println(Runtime.getRuntime().freeMemory());
              
          }
        }, 1*1*1000, 1*1*1000);// One second intervals
       }

I get this as a result(in bits):

115224312

113179200

113179200

...Same number(113179200)...forever

I want this function to auto refresh and change the number, but it does not do that. And I am unsure why. I have tried other methods(loops, other timers, etc.), but those do not work either.

If the amount of free memory isn't changing then why would the number change? Are you using memory elsewhere? — lucasvw, Apr 21 '17 at 14:09
Isn't memory suppose to not be constant so even if I do not do anything in the background the OS will always be changing memory usage. Which should in turn change the amount of free memory? Correct me if a am wrong please? — Alaa, Apr 21 '17 at 14:10
[`Runtime#freeMemory`](https://docs.oracle.com/javase/7/docs/api/java/lang/Runtime.html#freeMemory()) returns the amount of free memory in the *Java Virtual Machine*, not the OS — UnholySheep, Apr 21 '17 at 14:12
@Atlas see http://stackoverflow.com/questions/3571203/what-are-runtime-getruntime-totalmemory-and-freememory for more information on memory. the freememory method is only the memory within the java environment — lucasvw, Apr 21 '17 at 14:12
@UnholySheep So if I were to make a GUI application and perform an action will the number change because an event occurred? And lets just say this event required more memory. — Alaa, Apr 21 '17 at 14:16
If you use (or free) memory within your Java application then the number will change. Though you could just try it out instead of asking strangers on the internet. — UnholySheep, Apr 21 '17 at 14:20

score 2 · Accepted Answer · answered Apr 21 '17 at 14:31

I updated your code with some memory use after you start the timer check:

public static void main(String[] args) {
    Timer clock = new Timer();
    clock.schedule(new TimerTask() {
          @Override
          public void run() {
              System.out.print("Total: " + Runtime.getRuntime().totalMemory());
              System.out.println(" Free: " + Runtime.getRuntime().freeMemory());

          }
        }, 1*1*1000, 1*1*1000);// One second intervals

    // now use memory
    ArrayList<Object> arrays = new ArrayList<>();
    for (int i = 0; i < 1_000_000; ++i) {
        ArrayList<String> strings = new ArrayList<>();
        for (int j = 0; j < 1_000_000; ++j) {
            strings.add("" + j);
        }
        arrays.add(strings);
    }
    System.out.println("Loop complete");
}

And here's some of the output:

Total: 1203240960 Free: 752378848
Total: 1785200640 Free: 1107948136
Total: 3265265664 Free: 1522323408
Total: 3642228736 Free: 1180813496
Total: 5323096064 Free: 1982845016
Total: 5456265216 Free: 1627489984
Total: 7387742208 Free: 2923462928
Total: 7571767296 Free: 2455798264
Total: 7579631616 Free: 1657495280

As you can see, the amount of free memory (as well as total memory) is changing.

So as you fill elements in an array you begin to use memory which in turn changes the value of free memory and total memory. Lucas I was mistakenly assuming that the freeMemory() function returns information about the OS while in reality it was returning information about the JVM. That was useful. — Alaa, Apr 21 '17 at 14:36

Java timer class does not auto refresh a Runtime function?

1 Answers1