How do I get time in seconds since last frame? (Delta time)

Question

I am developing a game which there is no frame cap meaning it can run in 200 fps and in 40 fps, this is why I need delta time.

Now I've been trying to implement it but it didn't work.

Here is my code in the run() method (override of Runnable):

running = true;

Time.Start = System.currentTimeMillis() / 1000;
while (running) {
update();

render();

Time.Previous = (System.currentTimeMillis() - Start) / 1000;
}

And here is my "Time" class:

public class Time {
public static float Delta() {
return (System.currentTimeMillis() / 1000.0f - Start - Previous);
}
public static float Elapsed() {
return (System.currentTimeMillis() / 1000.0f - Start);
}

public static long Start;

public static long Previous;
}

Note that I am trying to get delta time in seconds in float. Thanks anyone for helping.

Answer 1

Nowhere in your code do you update the long Start. Essentially calculating the elapsed time from the start of the program -> current time.

To compute the elapsed time, it should have a start and an end variable:
public static void captureDeltaTime()
{
long start = System.currentTimeMillis();
slowCode();
long end = System.currentTimeMillis() - start; // Delta time in ms
float seconds = end / 1000.0f; // Delta time in s converted to float
System.out.println("Elapsed time in seconds: " + seconds);
}

By only setting the long "start" at the beginning, it will not correctly calculate the delta.