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System.javaAPI DocJ2ME MIDP 2.011038Thu Nov 07 12:02:26 GMT 2002java.lang

System

public final class System extends Object
The System class contains several useful class fields and methods. It cannot be instantiated.
author
Arthur van Hoff
version
1.110, 12/04/99 (CLDC 1.0, Spring 2000)
since
JDK1.0

Fields Summary
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.

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.

Constructors Summary
private System()
Don't let anyone instantiate this class

 
Methods Summary
public static native voidarraycopy(java.lang.Object src, int src_position, java.lang.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.)

param
src the source array.
param
src_position start position in the source array.
param
dst the destination array.
param
dst_position pos start 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 dst is null.

public static native longcurrentTimeMillis()
Returns the current time in milliseconds.

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

public static voidexit(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)

param
status exit status.
see
java.lang.Runtime#exit(int)

        Runtime.getRuntime().exit(status);
    
public static voidgc()
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()

see
java.lang.Runtime#gc()

        Runtime.getRuntime().gc();
    
private static java.io.PrintStreamgetConsoleOutput()


        
	return new PrintStream(new SystemOutputStream());
    
public static java.lang.StringgetProperty(java.lang.String key)
Gets the system property indicated by the specified key.

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.


                                         
        

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
           
                                           
                                         

                                                              
         

                                                                                             
         
        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.StringgetProperty0(java.lang.String key)

public static native intidentityHashCode(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.

param
x object for which the hashCode is to be calculated
return
the hashCode
since
JDK1.1