Java Interval


The Interval class will help us to measure time differences. We can (for example) use it very easily to find out how much time is left until a hero respawns after death or to find out how long a certain algorithm takes to execute.


Interval i = new Interval();

System.out.println("it took: " + i.value() + " ms")
// => it took 5 ms (etc.)

About System.currentTimeMillis()

The Java function System.currentTimeMillis() returns how long the system was running in milliseconds. Now if we do that once, wait a while, do it again and then subtract both results, we can easily measure time differences.


long start = System.currentTimeMillis();
long elapsed = System.currentTimeMillis() - start;

System.out.println("It took " + elapsed + " ms");


We want to use the above method and put it all into a simple class that does all the calculations for us. The Interval class will start counting the time when it was created and the .value() function will always return how much time has elapsed since start. In addition, we will also implement a .reset() function to restart the time counter.

public class Interval {        
    long m_start = System.currentTimeMillis();
    public long value() {
        return System.currentTimeMillis() - m_start;
    public void reset() {
        m_start = System.currentTimeMillis();

Note that m_start is being set when the object is created.

Usage Examples

In the first usage example we want to call the doStuff() function a few times, but only until 50 milliseconds are elapsed:

Interval i = new Interval();

// Do something for not longer than 50 milliseconds
while (i.value() < 50) {

The second example shows how the respawn problem mentioned above could be implemented with the Interval class:

Interval respawnInterval = null;

void playerTryToRespawn()
    // 10 seconds elapsed already?
    if (respawnInterval.value() >= 10000) {
        // respawn


A clean and simple implementation to solve a common problem when making games.