public final static InputStream in;
//标准输入流
public final static PrintStream out;
//标准输出流
public final static PrintStream err;
//标准错误流

  public static void main(String[] args) {

        int[] arr1 = { 0, 1, 2, 3, 4 };
        int[] arr2 = { 9, 9, 9, 9, 9 };

        System.arraycopy(arr1, 2, arr2, 0, 3);

        arr1[3] = 8;

        for (int i = 0; i < 5; i++)
            System.out.print(arr2[i] + " ");
            //2 3 4 9 9 
    }

  public static void main(String[] args) {
        String dirPath = System.getProperty("user.dir");
        System.out.println(dirPath);
        //输出工作目录  D:\Workspaces\MyEclipse 10\Algorithms（这是我的目录，每个人都不同）
    }

  public static void main(String[] args) {

        Date d = new Date();
        d = null;

        System.gc();
        // 在调用这句gc方法时，上面已经失去了d引用的new Date()被回收

    }

  public static void main(String[] args) {

        try {
            System.out.println("this is try");
            System.exit(0);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            System.out.println("this is finally");
        }

    }

    /* register the natives via the static initializer.
     *
     * VM will invoke the initializeSystemClass method to complete
     * the initialization for this class separated from clinit.
     * Note that to use properties set by the VM, see the constraints
     * described in the initializeSystemClass method.
     */
    private static native void registerNatives();
    static {
        registerNatives();
    }

    private static void initializeSystemClass() {

        props = new Properties();
        initProperties(props); 

        sun.misc.VM.saveAndRemoveProperties(props);

        lineSeparator = props.getProperty("line.separator");
        sun.misc.Version.init();

        FileInputStream fdIn = new FileInputStream(FileDescriptor.in);
        FileOutputStream fdOut = new FileOutputStream(FileDescriptor.out);
        FileOutputStream fdErr = new FileOutputStream(FileDescriptor.err);
        setIn0(new BufferedInputStream(fdIn));
        setOut0(newPrintStream(fdOut, props.getProperty("sun.stdout.encoding")));
        setErr0(newPrintStream(fdErr, props.getProperty("sun.stderr.encoding")));

        loadLibrary("zip");

        Terminator.setup();

        sun.misc.VM.initializeOSEnvironment();

        Thread current = Thread.currentThread();
        current.getThreadGroup().add(current);

        setJavaLangAccess();
        sun.misc.VM.booted();
    }

    public static void setIn(InputStream in) {
        checkIO();
        setIn0(in);
    }

    private static native void setIn0(InputStream in);