java - Calculating delta time

I'm trying to calculate deltaTime, but it's not correct.

What's wrong in my code?

//declared outside
private long timeSinceStart = System.nanoTime() / 1000;
private long oldTimeSinceStart = 0;
public static long deltaTime = 1;

while(running)

  timeSinceStart = System.nanoTime() / 1000;
  deltaTime = timeSinceStart - oldTimeSinceStart;
  oldTimeSinceStart = timeSinceStart;

Answer

System.nanoTime() returns the time in nanoseconds.

In order to get it in milliseconds, do System.nanoTime() / 1000000.

Here is an example how to calculate delta time properly.

long last_time = System.nanoTime();

while(running) {

    long time = System.nanoTime();
    int delta_time = (int) ((time - last_time) / 1000000);
    last_time = time;
}