java.lang
Class System

java.lang.Object
  |
  +--java.lang.System

public final class System

extends Object

Note: This class is built into the DVM. The System class contains several useful class fields and methods. It cannot be instantiated.

Among the facilities provided by the System class are standard input, standard output, and error output streams; access to externally defined "properties"; a means of loading files and libraries; and a utility method for quickly copying a portion of an array.

Since:

JDK1.0

Version:

1.111, 02/02/00

Author:

Arthur van Hoff

Field Summary

static PrintStream	err The "standard" error output stream.
static PrintStream	out The "standard" output stream.

Method Summary

static void	arraycopy(Object src, int src_position, Object dst, int dst_position, int length) Copies an array from the specified source array, beginning at the specified position, to the specified position of the destination array.
static long	currentTimeMillis() Returns the current time in milliseconds.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, toString

Field Detail

err

public static final PrintStream err

The "standard" error output stream. This stream is already open and ready to accept output data.

Typically this stream corresponds to display output or another output destination specified by the host environment or user. By convention, this output stream is used to display error messages or other information that should come to the immediate attention of a user even if the principal output stream, the value of the variable out, has been redirected to a file or other destination that is typically not continuously monitored.

out

public static final PrintStream out

The "standard" output stream. This stream is already open and ready to accept output data. Typically this stream corresponds to display output or another output destination specified by the host environment or user.

For simple stand-alone Java applications, a typical way to write a line of output data is:

     System.out.println(data)
 

See the println methods in class PrintStream.

See Also:

PrintStream.println(), PrintStream.println(boolean), PrintStream.println(char), PrintStream.println(char[]), PrintStream.println(double), PrintStream.println(float), PrintStream.println(int), PrintStream.println(long), PrintStream.println(java.lang.Object), PrintStream.println(java.lang.String)

Method Detail

arraycopy

public static void arraycopy(Object src,
                             int src_position,
                             Object dst,
                             int dst_position,
                             int length)

Copies an array from the specified source array, beginning at the specified position, to the specified position of the destination array. A subsequence of array components are copied from the source array referenced by src to the destination array referenced by dst. The number of components copied is equal to the length argument. The components at positions srcOffset through srcOffset+length-1 in the source array are copied into positions dstOffset through dstOffset+length-1, respectively, of the destination array.

If the src and dst arguments refer to the same array object, then the copying is performed as if the components at positions srcOffset through srcOffset+length-1 were first copied to a temporary array with length components and then the contents of the temporary array were copied into positions dstOffset through dstOffset+length-1 of the destination array.

If dst is null, then a NullPointerException is thrown.

If src is null, then a NullPointerException is thrown and the destination array is not modified.

Otherwise, if any of the following is true, an ArrayStoreException is thrown and the destination is not modified:

• The src argument refers to an object that is not an array.
• The dst argument refers to an object that is not an array.
• The src argument and dst argument refer to arrays whose component types are different primitive types.
• The src argument refers to an array with a primitive component type and the dst argument refers to an array with a reference component type.
• The src argument refers to an array with a reference component type and the dst argument refers to an array with a primitive component type.

Otherwise, if any of the following is true, an IndexOutOfBoundsException is thrown and the destination is not modified:

• The srcOffset argument is negative.
• The dstOffset argument is negative.
• The length argument is negative.
• srcOffset+length is greater than src.length, the length of the source array.
• dstOffset+length is greater than dst.length, the length of the destination array.

Otherwise, if any actual component of the source array from position srcOffset through srcOffset+length-1 cannot be converted to the component type of the destination array by assignment conversion, an ArrayStoreException is thrown. In this case, let k be the smallest nonnegative integer less than length such that src[srcOffset+k] cannot be converted to the component type of the destination array; when the exception is thrown, source array components from positions srcOffset through srcOffset+k-1 will already have been copied to destination array positions dstOffset through dstOffset+k-1 and no other positions of the destination array will have been modified. (Because of the restrictions already itemized, this paragraph effectively applies only to the situation where both arrays have component types that are reference types.)

Parameters:

src - the source array.

src_position - start position in the source array.

dst - the destination array.

dst_position - pos start position in the destination data.

length - the number of array elements to be copied.

Throws:

IndexOutOfBoundsException - if copying would cause access of data outside array bounds.

ArrayStoreException - if an element in the src array could not be stored into the dest array because of a type mismatch.

NullPointerException - if either src or dst is null.

currentTimeMillis

public static long currentTimeMillis()

Returns the current time in milliseconds.

See the description of the class Date for a discussion of slight discrepancies that may arise between "computer time" and coordinated universal time (UTC).

Returns:

the difference, measured in milliseconds, between the current time and midnight, January 1, 1970 UTC.

See Also:

Date