How to Returns the computer time in milliseconds?

public static long currentTimeMillis()
The value represents the number of milliseconds that has elapsed since January 1, 1970 UTC.
To get the string representation of the current computer time, use this:

System.out.println(new java.util.Date());
currentTimeMillis is useful if you want to time an operation.

public class MainClass {
public static void main(String[] a) {
long start = System.currentTimeMillis();

// block of code to time

long end = System.currentTimeMillis();
System.out.println("It took " + (end - start) + " milliseconds");