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java.lang.Objectjava.lang.System
@TransactionType(value=NOT_SUPPORTED) public final class System
The System
class contains several useful class fields and
methods. It cannot be instantiated.
This Java Card class is a subset of the CLDC 1.1 System class. Some interfaces, methods and/or variables have been pruned, and/or other methods simplified, in an effort to reduce the size of this class and/or eliminate dependencies on unsupported features.
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 srcOffset,
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. |
static long |
currentTimeMillis()
Returns the current time in milliseconds. |
static void |
gc()
Runs the garbage collector. |
static String |
getProperty(String key)
Gets the system property indicated by the specified key. |
static int |
identityHashCode(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(). |
Methods inherited from class java.lang.Object |
---|
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
---|
public static final PrintStream 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
.
PrintStream.println()
,
PrintStream.println(boolean)
,
PrintStream.println(char)
,
PrintStream.println(char[])
,
PrintStream.println(int)
,
PrintStream.println(long)
,
PrintStream.println(java.lang.Object)
,
PrintStream.println(java.lang.String)
public static final PrintStream 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.
Method Detail |
---|
public static long currentTimeMillis()
@TransactionType(value=SUPPORTS) public static void arraycopy(Object src, int srcOffset, Object dst, int dstOffset, int length)
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:
src
argument refers to an object that is not an
array.
dst
argument refers to an object that is not an
array.
src
argument and dst
argument
refer to arrays whose component types are different primitive types.
src
argument refers to an array with a primitive
component type and the dst
argument refers to an array
with a reference component type.
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:
srcOffset
argument is negative.
dstOffset
argument is negative.
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.)
src
- the source array.srcOffset
- start position in the source array.dst
- the destination array.dstOffset
- start position in the destination data.length
- the number of array elements to be copied.
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
.public static int identityHashCode(Object x)
x
- object for which the hashCode is to be calculated
public static String getProperty(String key)
key
- the name of the system property.
null
if there is no property with that key.
NullPointerException
- if key
is null
.
IllegalArgumentException
- if key
is empty.public static void gc()
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.gc()
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