System.currentTimeMillis vs System.nanoTime

public static long nanoTime()

long startTime = System.nanoTime();
// ... the code being measured ...
long estimatedTime = System.nanoTime() - startTime;

private void test() {
    System.out.println("currentTimeMillis: "+System.currentTimeMillis());
    System.out.println("nanoTime         : "+System.nanoTime());
    System.out.println();

    testNano(false);                                                            // to sync with currentTimeMillis() timer tick
    for(int xa=0; xa<10; xa++) {
        testNano(true);
        }
    }

private void testNano(boolean shw) {
    long strMS=System.currentTimeMillis();
    long strNS=System.nanoTime();
    long curMS;
    while((curMS=System.currentTimeMillis()) == strMS) {
        if(shw) { System.out.println("Nano: "+(System.nanoTime()-strNS)); }
        }
    if(shw) { System.out.println("Nano: "+(System.nanoTime()-strNS)+", Milli: "+(curMS-strMS)); }
    }

long startTimeMillis = System.currentTimeMillis();
    long startTimeNanos = System.nanoTime();

    long currentTimeMillis;
    while((currentTimeMillis = System.currentTimeMillis()) == startTimeMillis) {
    }


    System.out.println(System.nanoTime()-startTimeNanos);
    System.out.println(currentTimeMillis-startTimeMillis);