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java.lang.Objectjava.lang.System
public final class System
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.
lib |
Field Summary | |
---|---|
static ConsoleOutputStream |
err
The "standard" error output stream. |
static ConsoleInputStream |
in
The "standard" input stream. |
static ConsoleOutputStream |
out
The "standard" output stream. |
Constructor Summary | |
---|---|
System()
|
Method Summary | |
---|---|
static void |
arraycopy(Object src,
int srcPos,
Object dest,
int destPos,
int length)
Copies an array from the specified source array, beginning at the specified position, to the specified position of the destination array. |
static void |
setErr(ConsoleOutputStream newErr)
Reassigns the "standard" error output stream. |
static void |
setIn(ConsoleInputStream newIn)
Reassigns the "standard" input stream. |
static void |
setOut(ConsoleOutputStream newOut)
Reassigns the "standard" output stream. |
Methods inherited from class java.lang.Object |
---|
clone, equals, notifyAll, wait |
Field Detail |
---|
public static ConsoleOutputStream err
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.
ConsoleOutputStream
public static ConsoleInputStream in
ConsoleInputStream
public static ConsoleOutputStream out
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
.
ConsoleOutputStream
Constructor Detail |
---|
public System()
Method Detail |
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public static void arraycopy(Object src, int srcPos, Object dest, int destPos, int length)
src
to the destination array
referenced by dest
. The number of components copied is
equal to the length
argument. The components at
positions srcPos
through
srcPos+length-1
in the source array are copied into
positions destPos
through
destPos+length-1
, respectively, of the destination
array.
If the src
and dest
arguments refer to the
same array object, then the copying is performed as if the
components at positions srcPos
through
srcPos+length-1
were first copied to a temporary
array with length
components and then the contents of
the temporary array were copied into positions
destPos
through destPos+length-1
of the
destination array.
If dest
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:
src
argument refers to an object that is not an
array.
dest
argument refers to an object that is not an
array.
src
argument and dest
argument refer
to arrays whose component types are different primitive types.
src
argument refers to an array with a primitive
component type and the dest
argument refers to an array
with a reference component type.
src
argument refers to an array with a reference
component type and the dest
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:
srcPos
argument is negative.
destPos
argument is negative.
length
argument is negative.
srcPos+length
is greater than
src.length
, the length of the source array.
destPos+length
is greater than
dest.length
, the length of the destination array.
Otherwise, if any actual component of the source array from
position srcPos
through
srcPos+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[srcPos+
k]
cannot be converted to the component type of the destination
array; when the exception is thrown, source array components from
positions srcPos
through
srcPos+
k-1
will already have been copied to destination array positions
destPos
through
destPos+
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.)
A wrapper for Management.arraycopy(Object src, int srcPos, Object dest, int destPos, int length)
.
src
- the source array.srcPos
- starting position in the source array.dest
- the destination array.destPos
- starting position in the destination data.length
- the number of array elements to be copied.
java.lang.IndexOutOfBoundsException
- if copying would cause
access of data outside array bounds.
java.lang.ArrayStoreException
- if an element in the src
array could not be stored into the dest
array
because of a type mismatch.
java.lang.NullPointerException
- if either src
or
dest
is null
.public static void setErr(ConsoleOutputStream newErr)
First, if there is a security manager, its checkPermission
method is called with a RuntimePermission("setIO")
permission
to see if it's ok to reassign the "standard" error output stream.
newErr
- the new standard error output stream.
java.lang.SecurityException
- if a security manager exists and its
checkPermission
method doesn't allow
reassigning of the standard error output stream.SecurityManager.checkPermission(java.security.Permission)
,
RuntimePermission
public static void setIn(ConsoleInputStream newIn)
First, if there is a security manager, its checkPermission
method is called with a RuntimePermission("setIO")
permission
to see if it's ok to reassign the "standard" input stream.
newIn
- the new standard input stream.
java.lang.SecurityException
- if a security manager exists and its
checkPermission
method doesn't allow
reassigning of the standard input stream.SecurityManager.checkPermission(java.security.Permission)
,
RuntimePermission
public static void setOut(ConsoleOutputStream newOut)
First, if there is a security manager, its checkPermission
method is called with a RuntimePermission("setIO")
permission
to see if it's ok to reassign the "standard" output stream.
newOut
- the new standard output stream
java.lang.SecurityException
- if a security manager exists and its
checkPermission
method doesn't allow
reassigning of the standard output stream.SecurityManager.checkPermission(java.security.Permission)
,
RuntimePermission
|
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