System Programming - The Java Programming Language - page 987

long . Sophisticated applications may require more functional-
ity (see " Time, Dates, and Calendars " on page 695 ) .
public static long nanoTime()
Returns the current value, in nanoseconds, of the most pre-
cise available system timer. This method can only be used to
measure elapsed time and is not related to any notion of cal-
endar time or wall-clock time, and is not relative to the epoch.
Although the precision is in nanoseconds, there are no guar-
antees as to the accuracy.
public static void arraycopy(Object src, int srcPos, Object dst, int
dstPos, int count)
Copies the contents of the source array, starting at
src[srcPos] , to the destination array, starting at dst[dstPos] .
Exactly count elements will be copied. If an attempt is made
to access outside either array an IndexOutOfBoundsException is
thrown. If the values in the source array are not compatible
with the destination array an ArrayStoreException is thrown.
"Compatible" means that each object in the source array must
be assignable to the component type of the destination array.
For arrays of primitive types, the types must be the same,
not just assignable; arraycopy cannot be used to copy an array
of short to an array of int . The arraycopy method works cor-
rectly on overlapping arrays, so it can be used to copy one
part of an array over another part. You can, for example,
shift everything in an array one slot toward the beginning, as
shown in the method squeezeOut on page 318 .
public static int identityHashCode(Object obj)
Returns a hashcode for obj using the algorithm that Ob-
ject.hashCode defines. This allows algorithms that rely on iden-
tity hashing to work even if the class of obj overrides hashCode .