java.lang · java.base · since Java 1.0

System

declaration

public final class System

Process-level utilities: standard streams, environment and properties, time sources, and arraycopy. Uninstantiable — pure static surface.

Key methods

`static PrintStream out / err; static InputStream in`	The standard streams.
`static long currentTimeMillis()`	Wall-clock epoch millis — for timestamps.
`static long nanoTime()`	Monotonic elapsed-time source — for measuring durations (not wall time!).
`static String getenv(String) / getProperty(String)`	Environment variables / JVM properties.
`static void arraycopy(src, srcPos, dest, destPos, len)`	Fast native array copy.
`static void exit(int status)`	Terminates the JVM (runs shutdown hooks).