Systempublic final class System extends Object The System class contains several useful class fields
and methods. It cannot be instantiated. |
Fields Summary |
---|
public static final PrintStream | outThe "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 . | public static final PrintStream | errThe "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. |
Constructors Summary |
---|
private System()Don't let anyone instantiate this class
|
Methods Summary |
---|
public static native void | arraycopy(java.lang.Object src, int srcOffset, java.lang.Object dst, int dstOffset, 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.)
| public static native long | currentTimeMillis()Returns the current time in milliseconds.
| public static void | exit(int status)Terminates the currently running Java application. The
argument serves as a status code; by convention, a nonzero
status code indicates abnormal termination.
This method calls the exit method in class
Runtime . This method never returns normally.
The call System.exit(n) is effectively equivalent
to the call:
Runtime.getRuntime().exit(n)
Runtime.getRuntime().exit(status);
| public static void | gc()Runs the garbage collector.
Calling the gc method suggests that the Java Virtual
Machine expend effort toward recycling unused objects in order to
make the memory they currently occupy available for quick reuse.
When control returns from the method call, the Java Virtual
Machine has made a best effort to reclaim space from all discarded
objects.
The call System.gc() is effectively equivalent to the
call:
Runtime.getRuntime().gc()
Runtime.getRuntime().gc();
| private static java.io.PrintStream | getOutput()
return new PrintStream(new com.sun.cldc.io.ConsoleOutputStream());
| public static java.lang.String | getProperty(java.lang.String key)Gets the system property indicated by the specified key.
if (key == null) {
throw new NullPointerException("key can't be null");
}
if (key.equals("")) {
throw new IllegalArgumentException("key can't be empty");
}
return getProperty0(key);
| private static native java.lang.String | getProperty0(java.lang.String key)
| public static native int | identityHashCode(java.lang.Object x)Returns the same hashcode for the given object as
would be returned by the default method hashCode(),
whether or not the given object's class overrides
hashCode().
The hashcode for the null reference is zero.
|
|