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 and environment
* variables; a means of loading files and libraries; and a utility
* method for quickly copying a portion of an array.
*
* @author unascribed
* @since JDK1.0
*/
public final class System {
/** Don't let anyone instantiate this class */
private System() {
}
/**
* The "standard" input stream. This stream is already
* open and ready to supply input data. Typically this stream
* corresponds to keyboard input or another input source specified by
* the host environment or user.
*/
public final static InputStream in;
/**
* 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 java.io.PrintStream#println()
* @see java.io.PrintStream#println(boolean)
* @see java.io.PrintStream#println(char)
* @see java.io.PrintStream#println(char[])
* @see java.io.PrintStream#println(double)
* @see java.io.PrintStream#println(float)
* @see java.io.PrintStream#println(int)
* @see java.io.PrintStream#println(long)
* @see java.io.PrintStream#println(java.lang.Object)
* @see java.io.PrintStream#println(java.lang.String)
*/
public final static PrintStream out;
/**
* 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.
*/
public final static PrintStream err;
/**
* Dedicated lock for GC / Finalization logic.
*/
private static final Object LOCK = new Object();
/**
* Whether or not we need to do a GC before running the finalizers.
*/
private static boolean runGC;
/**
* If we just ran finalization, we might want to do a GC to free the finalized objects.
* This lets us do gc/runFinlization/gc sequences but prevents back to back System.gc().
*/
private static boolean justRanFinalization;
/**
* Reassigns the "standard" input stream.
*
*
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.
*
*
* @param in the new standard input stream.
*
* @throws SecurityException
* if a security manager exists and its
* checkPermission method doesn't allow
* reassigning of the standard input stream.
*
* @see SecurityManager#checkPermission
* @see java.lang.RuntimePermission
*
* @since JDK1.1
*/
public static void setIn(InputStream in) {
setIn0(in);
}
/**
* Reassigns the "standard" output stream.
*
*
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.
*
* @param out the new standard output stream
*
* @throws SecurityException
* if a security manager exists and its
* checkPermission method doesn't allow
* reassigning of the standard output stream.
*
* @see SecurityManager#checkPermission
* @see java.lang.RuntimePermission
*
* @since JDK1.1
*/
public static void setOut(PrintStream out) {
setOut0(out);
}
/**
* Reassigns the "standard" error output stream.
*
*
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.
*
* @param err the new standard error output stream.
*
* @throws SecurityException
* if a security manager exists and its
* checkPermission method doesn't allow
* reassigning of the standard error output stream.
*
* @see SecurityManager#checkPermission
* @see java.lang.RuntimePermission
*
* @since JDK1.1
*/
public static void setErr(PrintStream err) {
setErr0(err);
}
private static Console cons = null;
/**
* Returns the unique {@link java.io.Console Console} object associated
* with the current Java virtual machine, if any.
*
* @return The system console, if any, otherwise null.
*
* @since 1.6
*/
public static Console console() {
synchronized (System.class) {
if (cons == null) {
cons = Console.console();
}
return cons;
}
}
/**
* Returns the channel inherited from the entity that created this
* Java virtual machine.
*
*
This method returns the channel obtained by invoking the * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel * inheritedChannel} method of the system-wide default * {@link java.nio.channels.spi.SelectorProvider} object.
* *In addition to the network-oriented channels described in * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel * inheritedChannel}, this method may return other kinds of * channels in the future. * * @return The inherited channel, if any, otherwise null. * * @throws IOException * If an I/O error occurs * * @throws SecurityException * If a security manager is present and it does not * permit access to the channel. * * @since 1.5 */ public static Channel inheritedChannel() throws IOException { return SelectorProvider.provider().inheritedChannel(); } private static native void setIn0(InputStream in); private static native void setOut0(PrintStream out); private static native void setErr0(PrintStream err); /** * Throws {@code SecurityException} (except in case {@code sm == null}). * *
Security managers do not provide a secure environment for * executing untrusted code and are unsupported on Android. Untrusted code * cannot be safely isolated within a single VM on Android, so this method * always throws a {@code SecurityException} when passed a non-null SecurityManager * * @param sm a security manager * @throws SecurityException always, unless {@code sm == null} */ public static void setSecurityManager(SecurityManager sm) { if (sm != null) { throw new SecurityException(); } } /** * Always returns {@code null} in Android * * @return {@code null} in Android */ public static SecurityManager getSecurityManager() { // No-op on android. return null; } /** * Returns the current time in milliseconds. Note that * while the unit of time of the return value is a millisecond, * the granularity of the value depends on the underlying * operating system and may be larger. For example, many * operating systems measure time in units of tens of * 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).
*
* @return the difference, measured in milliseconds, between
* the current time and midnight, January 1, 1970 UTC.
* @see java.util.Date
*/
public static native long currentTimeMillis();
/**
* Returns the current value of the running Java Virtual Machine's
* high-resolution time source, in nanoseconds.
*
*
This method can only be used to measure elapsed time and is * not related to any other notion of system or wall-clock time. * The value returned represents nanoseconds since some fixed but * arbitrary origin time (perhaps in the future, so values * may be negative). The same origin is used by all invocations of * this method in an instance of a Java virtual machine; other * virtual machine instances are likely to use a different origin. * *
This method provides nanosecond precision, but not necessarily * nanosecond resolution (that is, how frequently the value changes) * - no guarantees are made except that the resolution is at least as * good as that of {@link #currentTimeMillis()}. * *
Differences in successive calls that span greater than * approximately 292 years (263 nanoseconds) will not * correctly compute elapsed time due to numerical overflow. * *
The values returned by this method become meaningful only when * the difference between two such values, obtained within the same * instance of a Java virtual machine, is computed. * *
For example, to measure how long some code takes to execute: *
{@code
* long startTime = System.nanoTime();
* // ... the code being measured ...
* long estimatedTime = System.nanoTime() - startTime;}
*
* To compare two nanoTime values *
{@code
* long t0 = System.nanoTime();
* ...
* long t1 = System.nanoTime();}
*
* one should use {@code t1 - t0 < 0}, not {@code t1 < t0},
* because of the possibility of numerical overflow.
*
* @return the current value of the running Java Virtual Machine's
* high-resolution time source, in nanoseconds
* @since 1.5
*/
public static native long nanoTime();
/**
* 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 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.)
*
* @param src the source array.
* @param srcPos starting position in the source array.
* @param dest the destination array.
* @param destPos starting position in the destination data.
* @param length the number of array elements to be copied.
* @exception IndexOutOfBoundsException if copying would cause
* access of data outside array bounds.
* @exception ArrayStoreException if an element in the src
* array could not be stored into the dest array
* because of a type mismatch.
* @exception NullPointerException if either src or
* dest is null.
*/
public static native void arraycopy(Object src, int srcPos,
Object dest, int destPos,
int length);
// ----- BEGIN android -----
/**
* The char array length threshold below which to use a Java
* (non-native) version of arraycopy() instead of the native
* version. See b/7103825.
*/
private static final int ARRAYCOPY_SHORT_CHAR_ARRAY_THRESHOLD = 32;
/**
* The char[] specialized version of arraycopy().
*
* @hide internal use only
*/
public static void arraycopy(char[] src, int srcPos, char[] dst, int dstPos, int length) {
if (src == null) {
throw new NullPointerException("src == null");
}
if (dst == null) {
throw new NullPointerException("dst == null");
}
if (srcPos < 0 || dstPos < 0 || length < 0 ||
srcPos > src.length - length || dstPos > dst.length - length) {
throw new ArrayIndexOutOfBoundsException(
"src.length=" + src.length + " srcPos=" + srcPos +
" dst.length=" + dst.length + " dstPos=" + dstPos + " length=" + length);
}
if (length <= ARRAYCOPY_SHORT_CHAR_ARRAY_THRESHOLD) {
// Copy char by char for shorter arrays.
if (src == dst && srcPos < dstPos && dstPos < srcPos + length) {
// Copy backward (to avoid overwriting elements before
// they are copied in case of an overlap on the same
// array.)
for (int i = length - 1; i >= 0; --i) {
dst[dstPos + i] = src[srcPos + i];
}
} else {
// Copy forward.
for (int i = 0; i < length; ++i) {
dst[dstPos + i] = src[srcPos + i];
}
}
} else {
// Call the native version for longer arrays.
arraycopyCharUnchecked(src, srcPos, dst, dstPos, length);
}
}
/**
* The char[] specialized, unchecked, native version of
* arraycopy(). This assumes error checking has been done.
*/
private static native void arraycopyCharUnchecked(char[] src, int srcPos,
char[] dst, int dstPos, int length);
/**
* The byte array length threshold below which to use a Java
* (non-native) version of arraycopy() instead of the native
* version. See b/7103825.
*/
private static final int ARRAYCOPY_SHORT_BYTE_ARRAY_THRESHOLD = 32;
/**
* The byte[] specialized version of arraycopy().
*
* @hide internal use only
*/
public static void arraycopy(byte[] src, int srcPos, byte[] dst, int dstPos, int length) {
if (src == null) {
throw new NullPointerException("src == null");
}
if (dst == null) {
throw new NullPointerException("dst == null");
}
if (srcPos < 0 || dstPos < 0 || length < 0 ||
srcPos > src.length - length || dstPos > dst.length - length) {
throw new ArrayIndexOutOfBoundsException(
"src.length=" + src.length + " srcPos=" + srcPos +
" dst.length=" + dst.length + " dstPos=" + dstPos + " length=" + length);
}
if (length <= ARRAYCOPY_SHORT_BYTE_ARRAY_THRESHOLD) {
// Copy byte by byte for shorter arrays.
if (src == dst && srcPos < dstPos && dstPos < srcPos + length) {
// Copy backward (to avoid overwriting elements before
// they are copied in case of an overlap on the same
// array.)
for (int i = length - 1; i >= 0; --i) {
dst[dstPos + i] = src[srcPos + i];
}
} else {
// Copy forward.
for (int i = 0; i < length; ++i) {
dst[dstPos + i] = src[srcPos + i];
}
}
} else {
// Call the native version for longer arrays.
arraycopyByteUnchecked(src, srcPos, dst, dstPos, length);
}
}
/**
* The byte[] specialized, unchecked, native version of
* arraycopy(). This assumes error checking has been done.
*/
private static native void arraycopyByteUnchecked(byte[] src, int srcPos,
byte[] dst, int dstPos, int length);
/**
* The short array length threshold below which to use a Java
* (non-native) version of arraycopy() instead of the native
* version. See b/7103825.
*/
private static final int ARRAYCOPY_SHORT_SHORT_ARRAY_THRESHOLD = 32;
/**
* The short[] specialized version of arraycopy().
*
* @hide internal use only
*/
public static void arraycopy(short[] src, int srcPos, short[] dst, int dstPos, int length) {
if (src == null) {
throw new NullPointerException("src == null");
}
if (dst == null) {
throw new NullPointerException("dst == null");
}
if (srcPos < 0 || dstPos < 0 || length < 0 ||
srcPos > src.length - length || dstPos > dst.length - length) {
throw new ArrayIndexOutOfBoundsException(
"src.length=" + src.length + " srcPos=" + srcPos +
" dst.length=" + dst.length + " dstPos=" + dstPos + " length=" + length);
}
if (length <= ARRAYCOPY_SHORT_SHORT_ARRAY_THRESHOLD) {
// Copy short by short for shorter arrays.
if (src == dst && srcPos < dstPos && dstPos < srcPos + length) {
// Copy backward (to avoid overwriting elements before
// they are copied in case of an overlap on the same
// array.)
for (int i = length - 1; i >= 0; --i) {
dst[dstPos + i] = src[srcPos + i];
}
} else {
// Copy forward.
for (int i = 0; i < length; ++i) {
dst[dstPos + i] = src[srcPos + i];
}
}
} else {
// Call the native version for longer arrays.
arraycopyShortUnchecked(src, srcPos, dst, dstPos, length);
}
}
/**
* The short[] specialized, unchecked, native version of
* arraycopy(). This assumes error checking has been done.
*/
private static native void arraycopyShortUnchecked(short[] src, int srcPos,
short[] dst, int dstPos, int length);
/**
* The short array length threshold below which to use a Java
* (non-native) version of arraycopy() instead of the native
* version. See b/7103825.
*/
private static final int ARRAYCOPY_SHORT_INT_ARRAY_THRESHOLD = 32;
/**
* The int[] specialized version of arraycopy().
*
* @hide internal use only
*/
public static void arraycopy(int[] src, int srcPos, int[] dst, int dstPos, int length) {
if (src == null) {
throw new NullPointerException("src == null");
}
if (dst == null) {
throw new NullPointerException("dst == null");
}
if (srcPos < 0 || dstPos < 0 || length < 0 ||
srcPos > src.length - length || dstPos > dst.length - length) {
throw new ArrayIndexOutOfBoundsException(
"src.length=" + src.length + " srcPos=" + srcPos +
" dst.length=" + dst.length + " dstPos=" + dstPos + " length=" + length);
}
if (length <= ARRAYCOPY_SHORT_INT_ARRAY_THRESHOLD) {
// Copy int by int for shorter arrays.
if (src == dst && srcPos < dstPos && dstPos < srcPos + length) {
// Copy backward (to avoid overwriting elements before
// they are copied in case of an overlap on the same
// array.)
for (int i = length - 1; i >= 0; --i) {
dst[dstPos + i] = src[srcPos + i];
}
} else {
// Copy forward.
for (int i = 0; i < length; ++i) {
dst[dstPos + i] = src[srcPos + i];
}
}
} else {
// Call the native version for longer arrays.
arraycopyIntUnchecked(src, srcPos, dst, dstPos, length);
}
}
/**
* The int[] specialized, unchecked, native version of
* arraycopy(). This assumes error checking has been done.
*/
private static native void arraycopyIntUnchecked(int[] src, int srcPos,
int[] dst, int dstPos, int length);
/**
* The short array length threshold below which to use a Java
* (non-native) version of arraycopy() instead of the native
* version. See b/7103825.
*/
private static final int ARRAYCOPY_SHORT_LONG_ARRAY_THRESHOLD = 32;
/**
* The long[] specialized version of arraycopy().
*
* @hide internal use only
*/
public static void arraycopy(long[] src, int srcPos, long[] dst, int dstPos, int length) {
if (src == null) {
throw new NullPointerException("src == null");
}
if (dst == null) {
throw new NullPointerException("dst == null");
}
if (srcPos < 0 || dstPos < 0 || length < 0 ||
srcPos > src.length - length || dstPos > dst.length - length) {
throw new ArrayIndexOutOfBoundsException(
"src.length=" + src.length + " srcPos=" + srcPos +
" dst.length=" + dst.length + " dstPos=" + dstPos + " length=" + length);
}
if (length <= ARRAYCOPY_SHORT_LONG_ARRAY_THRESHOLD) {
// Copy long by long for shorter arrays.
if (src == dst && srcPos < dstPos && dstPos < srcPos + length) {
// Copy backward (to avoid overwriting elements before
// they are copied in case of an overlap on the same
// array.)
for (int i = length - 1; i >= 0; --i) {
dst[dstPos + i] = src[srcPos + i];
}
} else {
// Copy forward.
for (int i = 0; i < length; ++i) {
dst[dstPos + i] = src[srcPos + i];
}
}
} else {
// Call the native version for longer arrays.
arraycopyLongUnchecked(src, srcPos, dst, dstPos, length);
}
}
/**
* The long[] specialized, unchecked, native version of
* arraycopy(). This assumes error checking has been done.
*/
private static native void arraycopyLongUnchecked(long[] src, int srcPos,
long[] dst, int dstPos, int length);
/**
* The short array length threshold below which to use a Java
* (non-native) version of arraycopy() instead of the native
* version. See b/7103825.
*/
private static final int ARRAYCOPY_SHORT_FLOAT_ARRAY_THRESHOLD = 32;
/**
* The float[] specialized version of arraycopy().
*
* @hide internal use only
*/
public static void arraycopy(float[] src, int srcPos, float[] dst, int dstPos, int length) {
if (src == null) {
throw new NullPointerException("src == null");
}
if (dst == null) {
throw new NullPointerException("dst == null");
}
if (srcPos < 0 || dstPos < 0 || length < 0 ||
srcPos > src.length - length || dstPos > dst.length - length) {
throw new ArrayIndexOutOfBoundsException(
"src.length=" + src.length + " srcPos=" + srcPos +
" dst.length=" + dst.length + " dstPos=" + dstPos + " length=" + length);
}
if (length <= ARRAYCOPY_SHORT_FLOAT_ARRAY_THRESHOLD) {
// Copy float by float for shorter arrays.
if (src == dst && srcPos < dstPos && dstPos < srcPos + length) {
// Copy backward (to avoid overwriting elements before
// they are copied in case of an overlap on the same
// array.)
for (int i = length - 1; i >= 0; --i) {
dst[dstPos + i] = src[srcPos + i];
}
} else {
// Copy forward.
for (int i = 0; i < length; ++i) {
dst[dstPos + i] = src[srcPos + i];
}
}
} else {
// Call the native version for floater arrays.
arraycopyFloatUnchecked(src, srcPos, dst, dstPos, length);
}
}
/**
* The float[] specialized, unchecked, native version of
* arraycopy(). This assumes error checking has been done.
*/
private static native void arraycopyFloatUnchecked(float[] src, int srcPos,
float[] dst, int dstPos, int length);
/**
* The short array length threshold below which to use a Java
* (non-native) version of arraycopy() instead of the native
* version. See b/7103825.
*/
private static final int ARRAYCOPY_SHORT_DOUBLE_ARRAY_THRESHOLD = 32;
/**
* The double[] specialized version of arraycopy().
*
* @hide internal use only
*/
public static void arraycopy(double[] src, int srcPos, double[] dst, int dstPos, int length) {
if (src == null) {
throw new NullPointerException("src == null");
}
if (dst == null) {
throw new NullPointerException("dst == null");
}
if (srcPos < 0 || dstPos < 0 || length < 0 ||
srcPos > src.length - length || dstPos > dst.length - length) {
throw new ArrayIndexOutOfBoundsException(
"src.length=" + src.length + " srcPos=" + srcPos +
" dst.length=" + dst.length + " dstPos=" + dstPos + " length=" + length);
}
if (length <= ARRAYCOPY_SHORT_DOUBLE_ARRAY_THRESHOLD) {
// Copy double by double for shorter arrays.
if (src == dst && srcPos < dstPos && dstPos < srcPos + length) {
// Copy backward (to avoid overwriting elements before
// they are copied in case of an overlap on the same
// array.)
for (int i = length - 1; i >= 0; --i) {
dst[dstPos + i] = src[srcPos + i];
}
} else {
// Copy forward.
for (int i = 0; i < length; ++i) {
dst[dstPos + i] = src[srcPos + i];
}
}
} else {
// Call the native version for floater arrays.
arraycopyDoubleUnchecked(src, srcPos, dst, dstPos, length);
}
}
/**
* The double[] specialized, unchecked, native version of
* arraycopy(). This assumes error checking has been done.
*/
private static native void arraycopyDoubleUnchecked(double[] src, int srcPos,
double[] dst, int dstPos, int length);
/**
* The short array length threshold below which to use a Java
* (non-native) version of arraycopy() instead of the native
* version. See b/7103825.
*/
private static final int ARRAYCOPY_SHORT_BOOLEAN_ARRAY_THRESHOLD = 32;
/**
* The boolean[] specialized version of arraycopy().
*
* @hide internal use only
*/
public static void arraycopy(boolean[] src, int srcPos, boolean[] dst, int dstPos, int length) {
if (src == null) {
throw new NullPointerException("src == null");
}
if (dst == null) {
throw new NullPointerException("dst == null");
}
if (srcPos < 0 || dstPos < 0 || length < 0 ||
srcPos > src.length - length || dstPos > dst.length - length) {
throw new ArrayIndexOutOfBoundsException(
"src.length=" + src.length + " srcPos=" + srcPos +
" dst.length=" + dst.length + " dstPos=" + dstPos + " length=" + length);
}
if (length <= ARRAYCOPY_SHORT_BOOLEAN_ARRAY_THRESHOLD) {
// Copy boolean by boolean for shorter arrays.
if (src == dst && srcPos < dstPos && dstPos < srcPos + length) {
// Copy backward (to avoid overwriting elements before
// they are copied in case of an overlap on the same
// array.)
for (int i = length - 1; i >= 0; --i) {
dst[dstPos + i] = src[srcPos + i];
}
} else {
// Copy forward.
for (int i = 0; i < length; ++i) {
dst[dstPos + i] = src[srcPos + i];
}
}
} else {
// Call the native version for floater arrays.
arraycopyBooleanUnchecked(src, srcPos, dst, dstPos, length);
}
}
/**
* The boolean[] specialized, unchecked, native version of
* arraycopy(). This assumes error checking has been done.
*/
private static native void arraycopyBooleanUnchecked(boolean[] src, int srcPos,
boolean[] dst, int dstPos, int length);
// ----- END android -----
/**
* Returns the same hash code for the given object as
* would be returned by the default method hashCode(),
* whether or not the given object's class overrides
* hashCode().
* The hash code for the null reference is zero.
*
* @param x object for which the hashCode is to be calculated
* @return the hashCode
* @since JDK1.1
*/
public static native int identityHashCode(Object x);
/**
* System properties. The following properties are guaranteed to be defined:
*
The following properties are always provided by the Dalvik VM:
*| Name | Meaning | Example |
| file.separator | {@link java.io.File#separator} | {@code /} |
| java.class.path | System class path | {@code .} |
| java.class.version | (Not useful on Android) | {@code 50.0} |
| java.compiler | (Not useful on Android) | Empty |
| java.ext.dirs | (Not useful on Android) | Empty |
| java.home | Location of the VM on the file system | {@code /system} |
| java.io.tmpdir | See {@link java.io.File#createTempFile} | {@code /sdcard} |
| java.library.path | Search path for JNI libraries | {@code /vendor/lib:/system/lib} |
| java.vendor | Human-readable VM vendor | {@code The Android Project} |
| java.vendor.url | URL for VM vendor's web site | {@code http://www.android.com/} |
| java.version | (Not useful on Android) | {@code 0} |
| java.specification.version | VM libraries version | {@code 0.9} |
| java.specification.vendor | VM libraries vendor | {@code The Android Project} |
| java.specification.name | VM libraries name | {@code Dalvik Core Library} |
| java.vm.version | VM implementation version | {@code 1.2.0} |
| java.vm.vendor | VM implementation vendor | {@code The Android Project} |
| java.vm.name | VM implementation name | {@code Dalvik} |
| java.vm.specification.version | VM specification version | {@code 0.9} |
| java.vm.specification.vendor | VM specification vendor | {@code The Android Project} |
| java.vm.specification.name | VM specification name | {@code Dalvik Virtual Machine Specification} |
| line.separator | The system line separator | {@code \n} |
| os.arch | OS architecture | {@code armv7l} |
| os.name | OS (kernel) name | {@code Linux} |
| os.version | OS (kernel) version | {@code 2.6.32.9-g103d848} |
| path.separator | See {@link java.io.File#pathSeparator} | {@code :} |
| user.dir | Base of non-absolute paths | {@code /} |
| user.home | (Not useful on Android) | Empty |
| user.name | (Not useful on Android) | Empty |
* Multiple paths in a system property value are separated by the path * separator character of the platform. * * @return the system properties * @see #setProperties * @see java.util.Properties */ public static Properties getProperties() { return props; } /** * Returns the system-dependent line separator string. It always * returns the same value - the initial value of the {@linkplain * #getProperty(String) system property} {@code line.separator}. * *
On UNIX systems, it returns {@code "\n"}; on Microsoft
* Windows systems it returns {@code "\r\n"}.
*/
public static String lineSeparator() {
return lineSeparator;
}
private static String lineSeparator;
// Comment replaced with android one.
/**
* Attempts to set all system properties. Copies all properties from
* {@code p} and discards system properties that are read only and cannot
* be modified. See {@link #getProperty} for a list of such properties.
*/
public static void setProperties(Properties props) {
Properties baseProperties = new PropertiesWithNonOverrideableDefaults(unchangeableProps);
if (props != null) {
baseProperties.putAll(props);
} else {
setDefaultChangeableProperties(baseProperties);
}
System.props = baseProperties;
}
/**
* Gets the system property indicated by the specified key.
*
* If there is no current set of system properties, a set of system
* properties is first created and initialized in the same manner as
* for the getProperties method.
*
* @param key the name of the system property.
* @return the string value of the system property,
* or null if there is no property with that key.
*
* @exception NullPointerException if key is
* null.
* @exception IllegalArgumentException if key is empty.
* @see #setProperty
* @see java.lang.System#getProperties()
*/
public static String getProperty(String key) {
checkKey(key);
return props.getProperty(key);
}
/**
* Gets the system property indicated by the specified key.
*
* First, if there is a security manager, its
* checkPropertyAccess method is called with the
* key as its argument.
*
* If there is no current set of system properties, a set of system
* properties is first created and initialized in the same manner as
* for the getProperties method.
*
* @param key the name of the system property.
* @param def a default value.
* @return the string value of the system property,
* or the default value if there is no property with that key.
*
* @exception NullPointerException if key is
* null.
* @exception IllegalArgumentException if key is empty.
* @see #setProperty
* @see java.lang.System#getProperties()
*/
public static String getProperty(String key, String def) {
checkKey(key);
return props.getProperty(key, def);
}
/**
* Sets the system property indicated by the specified key.
*
* @param key the name of the system property.
* @param value the value of the system property.
* @return the previous value of the system property,
* or null if it did not have one.
*
* @exception NullPointerException if key or
* value is null.
* @exception IllegalArgumentException if key is empty.
* @see #getProperty
* @see java.lang.System#getProperty(java.lang.String)
* @see java.lang.System#getProperty(java.lang.String, java.lang.String)
* @since 1.2
*/
public static String setProperty(String key, String value) {
checkKey(key);
return (String) props.setProperty(key, value);
}
/**
* Removes the system property indicated by the specified key.
*
* @param key the name of the system property to be removed.
* @return the previous string value of the system property,
* or null if there was no property with that key.
*
* @exception NullPointerException if key is
* null.
* @exception IllegalArgumentException if key is empty.
* @see #getProperty
* @see #setProperty
* @see java.util.Properties
* @since 1.5
*/
public static String clearProperty(String key) {
checkKey(key);
return (String) props.remove(key);
}
private static void checkKey(String key) {
if (key == null) {
throw new NullPointerException("key can't be null");
}
if (key.equals("")) {
throw new IllegalArgumentException("key can't be empty");
}
}
/**
* Gets the value of the specified environment variable. An
* environment variable is a system-dependent external named
* value.
*
*
If a security manager exists, its
* {@link SecurityManager#checkPermission checkPermission}
* method is called with a
* {@link RuntimePermission}("getenv."+name)
* permission. This may result in a {@link SecurityException}
* being thrown. If no exception is thrown the value of the
* variable name is returned.
*
*
System
* properties and environment variables are both
* conceptually mappings between names and values. Both
* mechanisms can be used to pass user-defined information to a
* Java process. Environment variables have a more global effect,
* because they are visible to all descendants of the process
* which defines them, not just the immediate Java subprocess.
* They can have subtly different semantics, such as case
* insensitivity, on different operating systems. For these
* reasons, environment variables are more likely to have
* unintended side effects. It is best to use system properties
* where possible. Environment variables should be used when a
* global effect is desired, or when an external system interface
* requires an environment variable (such as PATH).
*
*
On UNIX systems the alphabetic case of name is
* typically significant, while on Microsoft Windows systems it is
* typically not. For example, the expression
* System.getenv("FOO").equals(System.getenv("foo"))
* is likely to be true on Microsoft Windows.
*
* @param name the name of the environment variable
* @return the string value of the variable, or null
* if the variable is not defined in the system environment
* @throws NullPointerException if name is null
* @throws SecurityException
* if a security manager exists and its
* {@link SecurityManager#checkPermission checkPermission}
* method doesn't allow access to the environment variable
* name
* @see #getenv()
* @see ProcessBuilder#environment()
*/
public static String getenv(String name) {
if (name == null) {
throw new NullPointerException("name == null");
}
return Libcore.os.getenv(name);
}
/**
* Returns an unmodifiable string map view of the current system environment.
* The environment is a system-dependent mapping from names to
* values which is passed from parent to child processes.
*
*
If the system does not support environment variables, an * empty map is returned. * *
The returned map will never contain null keys or values. * Attempting to query the presence of a null key or value will * throw a {@link NullPointerException}. Attempting to query * the presence of a key or value which is not of type * {@link String} will throw a {@link ClassCastException}. * *
The returned map and its collection views may not obey the * general contract of the {@link Object#equals} and * {@link Object#hashCode} methods. * *
The returned map is typically case-sensitive on all platforms. * *
If a security manager exists, its
* {@link SecurityManager#checkPermission checkPermission}
* method is called with a
* {@link RuntimePermission}("getenv.*")
* permission. This may result in a {@link SecurityException} being
* thrown.
*
*
When passing information to a Java subprocess,
* system properties
* are generally preferred over environment variables.
*
* @return the environment as a map of variable names to values
* @throws SecurityException
* if a security manager exists and its
* {@link SecurityManager#checkPermission checkPermission}
* method doesn't allow access to the process environment
* @see #getenv(String)
* @see ProcessBuilder#environment()
* @since 1.5
*/
public static java.util.Map
* This method calls the
* The call
* Calling the
* The call
* Calling this method suggests that the Java Virtual Machine expend
* effort toward running the
* The call If there is a security manager,
* its
* The call
* The call exit method in class
* Runtime. This method never returns normally.
* System.exit(n) is effectively equivalent to
* the call:
*
*
* @param status exit status.
* @throws SecurityException
* if a security manager exists and its
* Runtime.getRuntime().exit(n)
* checkExit
* method doesn't allow exit with the specified status.
* @see java.lang.Runtime#exit(int)
*/
public static void exit(int status) {
Runtime.getRuntime().exit(status);
}
/**
* Runs the garbage collector.
* 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.
* System.gc() is effectively equivalent to the
* call:
*
*
* @see java.lang.Runtime#gc()
*/
public static void gc() {
boolean shouldRunGC;
synchronized (LOCK) {
shouldRunGC = justRanFinalization;
if (shouldRunGC) {
justRanFinalization = false;
} else {
runGC = true;
}
}
if (shouldRunGC) {
Runtime.getRuntime().gc();
}
}
/**
* Runs the finalization methods of any objects pending finalization.
*
* Runtime.getRuntime().gc()
* finalize methods of objects
* that have been found to be discarded but whose finalize
* methods have not yet been run. When control returns from the
* method call, the Java Virtual Machine has made a best effort to
* complete all outstanding finalizations.
* System.runFinalization() is effectively
* equivalent to the call:
*
*
* @see java.lang.Runtime#runFinalization()
*/
public static void runFinalization() {
boolean shouldRunGC;
synchronized (LOCK) {
shouldRunGC = runGC;
runGC = false;
}
if (shouldRunGC) {
Runtime.getRuntime().gc();
}
Runtime.getRuntime().runFinalization();
synchronized (LOCK) {
justRanFinalization = true;
}
}
/**
* Enable or disable finalization on exit; doing so specifies that the
* finalizers of all objects that have finalizers that have not yet been
* automatically invoked are to be run before the Java runtime exits.
* By default, finalization on exit is disabled.
*
*
* Runtime.getRuntime().runFinalization()
* checkExit method is first called
* with 0 as its argument to ensure the exit is allowed.
* This could result in a SecurityException.
*
* @deprecated This method is inherently unsafe. It may result in
* finalizers being called on live objects while other threads are
* concurrently manipulating those objects, resulting in erratic
* behavior or deadlock.
* @param value indicating enabling or disabling of finalization
* @throws SecurityException
* if a security manager exists and its checkExit
* method doesn't allow the exit.
*
* @see java.lang.Runtime#exit(int)
* @see java.lang.Runtime#gc()
* @see java.lang.SecurityManager#checkExit(int)
* @since JDK1.1
*/
@Deprecated
public static void runFinalizersOnExit(boolean value) {
Runtime.getRuntime().runFinalizersOnExit(value);
}
/**
* Loads a code file with the specified filename from the local file
* system as a dynamic library. The filename
* argument must be a complete path name.
* System.load(name) is effectively equivalent
* to the call:
*
*
* @param filename the file to load.
* @exception SecurityException if a security manager exists and its
*
* Runtime.getRuntime().load(name)
* checkLink method doesn't allow
* loading of the specified dynamic library
* @exception UnsatisfiedLinkError if the file does not exist.
* @exception NullPointerException if filename is
* null
* @see java.lang.Runtime#load(java.lang.String)
* @see java.lang.SecurityManager#checkLink(java.lang.String)
*/
public static void load(String filename) {
Runtime.getRuntime().load0(VMStack.getStackClass1(), filename);
}
/**
* Loads the system library specified by the libname
* argument. The manner in which a library name is mapped to the
* actual system library is system dependent.
* System.loadLibrary(name) is effectively
* equivalent to the call
*
*
* @param libname the name of the library.
* @exception SecurityException if a security manager exists and its
*
* Runtime.getRuntime().loadLibrary(name)
* checkLink method doesn't allow
* loading of the specified dynamic library
* @exception UnsatisfiedLinkError if the library does not exist.
* @exception NullPointerException if libname is
* null
* @see java.lang.Runtime#loadLibrary(java.lang.String)
* @see java.lang.SecurityManager#checkLink(java.lang.String)
*/
public static void loadLibrary(String libname) {
Runtime.getRuntime().loadLibrary0(VMStack.getCallingClassLoader(), libname);
}
/**
* Maps a library name into a platform-specific string representing
* a native library.
*
* @param libname the name of the library.
* @return a platform-dependent native library name.
* @exception NullPointerException if libname is
* null
* @see java.lang.System#loadLibrary(java.lang.String)
* @see java.lang.ClassLoader#findLibrary(java.lang.String)
* @since 1.2
*/
public static native String mapLibraryName(String libname);
/**
* Initialize the system class. Called after thread initialization.
*/
static {
unchangeableProps = initUnchangeableSystemProperties();
props = initProperties();
addLegacyLocaleSystemProperties();
sun.misc.Version.initSystemProperties();
// TODO: Confirm that this isn't something super important.
// sun.misc.VM.saveAndRemoveProperties(props);
lineSeparator = props.getProperty("line.separator");
FileInputStream fdIn = new FileInputStream(FileDescriptor.in);
FileOutputStream fdOut = new FileOutputStream(FileDescriptor.out);
FileOutputStream fdErr = new FileOutputStream(FileDescriptor.err);
in = new BufferedInputStream(fdIn);
out = new PrintStream(fdOut);
err = new PrintStream(fdErr);
// Initialize any miscellenous operating system settings that need to be
// set for the class libraries. Currently this is no-op everywhere except
// for Windows where the process-wide error mode is set before the java.io
// classes are used.
sun.misc.VM.initializeOSEnvironment();
// Subsystems that are invoked during initialization can invoke
// sun.misc.VM.isBooted() in order to avoid doing things that should
// wait until the application class loader has been set up.
// IMPORTANT: Ensure that this remains the last initialization action!
sun.misc.VM.booted();
}
/**
* @hide internal use only
*/
public static void logE(String message) {
log('E', message, null);
}
/**
* @hide internal use only
*/
public static void logE(String message, Throwable th) {
log('E', message, th);
}
/**
* @hide internal use only
*/
public static void logI(String message) {
log('I', message, null);
}
/**
* @hide internal use only
*/
public static void logI(String message, Throwable th) {
log('I', message, th);
}
/**
* @hide internal use only
*/
public static void logW(String message) {
log('W', message, null);
}
/**
* @hide internal use only
*/
public static void logW(String message, Throwable th) {
log('W', message, th);
}
private static native void log(char type, String message, Throwable th);
}