Analysis of this week:

Viewpoint of Africa and the United States is still bearish, we try to find resistance short, the whole Africa and the United States in the early fall the most powerful EU, Africa and the United States under the next phase of decline in attention to the strength of conversion, the appropriate focus of attention under the sterling and Australian dollars and so on. The February settlement pay attention to what the Japanese fiscal year, the United States and Japan have a greater short-term fluctuations, we may be appropriate to refer to the history of the stock market this month, changes in the U.S. and Japan.

Pounds this week, the United States resistance to 1.6070, and 6180 to monitor the operation of the resistance, short-term long-short conversions continue to be 1.6280 as the threshold, because last week, five the next break 1.6070, then we dominated the next phase in order to empty GU. Supporting the 1.5830 and 1.5700 to note that the GU’s largest us look at 1.5660 near the support, and then produce a rebound and then started to decline. The main point of view the same space.

Europe and the United States is currently Quotes clearly suggest that you do not easily grasp the end and grab a rebound advantage of the opportunity to trade a good point. Reference peripheral resistance from 1.3980 to 4030 the regional resistance, the biggest weekly resistance at 1.4115. Break below 1.3755, it will be challenging 1.35, or 1.33 file support.
(And the original Financial News)

The United States and Japan-week wait time being, we expect to continue to range UJ shocks, but would like the transaction can be 93.77 loss, looking for better resistance to short-based.

U.S. stocks gold commodity money because the impact of oil will continue to fall, and adverse commodity currencies, so the operation recommended as far as possible in order to empty the direction of commodity currencies to do, whether it is to recover a single or a callback do this on his own to the reference and grasp the .

U.S. stocks have peaked temporarily take note of the callback can be, then the right Africa and the United States is also a disadvantage.

Gold is also still down, pay attention to vibration amplitude, the main bearishness.

China A shares there will be low, are not suited Jiancang, we can wait for 2100-2300 District, part of the right to establish positions, 08-year low of 1700 files are not necessarily under the temporary break in 2010, it is proposed that we present a few years of the A shares on the reference band transactions, non-greedy big profits. High this year, will probably appear in 3800 or the 4300-4500 region. However, careful look at high-A shares.

February Monthly analysis of a brief reference to Quotes

We pay attention to the relevant European and national news events of interest to analyze the progress of what market conditions change.

Africa and the United States as a whole in February there will be low, so the operation on the band to a certain degree of air-American behavior is acceptable. But the medium-term is unlikely, after all, for many years before the big event of the mid-Quotes. The current band of operation for transactions, so a good grasp of the rhythm of their own transactions, the market-band compatibility with shocks.

Pounds pressure obviously, to remind you any empty single-band refer to resistance loss DC to several factors, 1.6280 area 1.6455 zone, from 1.6650 to 6730 area, only the Po Wei GU can change the main view, to challenge a . 7040 and 1.83 file opportunities. Otherwise, we continue to maintain GU will first of this year under the 1.53 or 1.44 / 1.47 file point of view. These support areas that we will consider the medium-term reference to the possibility of more than pounds.

The key medium-term support for the euro from 1.33 to 1.3550 area, while a. 28/3000 areas not under the break, the next break will completely change the EU’s view. Any EU pre-mid-air alone to 1.4200, and 1.4330, and 1.4580 for the transferred momentum in a reference to loss-bit, Powei can change the views of the EU.

US-Japan simple, any empty alone 93.77 reference to loss-bit, Po Wei will change the views of the main U.S. and Japanese short view, did not break before the main air UJ look the same, breaking below 87.35, and 84.8, if it would be rapidly achieve 79/80 file, so we take a good rhythm to trade.

The commodity currencies, we can refer to the main EU GU Africa and the United States to carry out the direction of a certain currency transactions to grasp.

Gold Oil has no long, it is recommended to empty the main subject, we must wait patiently and so a good atmosphere for the overall market appears to be taken.

Reminder: Any transaction please refer to their own fund management from risk control and strictly implement the principles of good discipline and trading their own criteria before they can. Any price can be given to air all right, because the idea of each transaction is different from the period of time and space to see the different cycles. Trading system is completely different.

The United States and Mexico border is home to a calculating farmers. Others are living in farming, and he has open a new path, only 10 U.S. dollars on its own will be able to enjoy the savings can be regarded as a well-off life.

Good morning, and his side of the hotel in the United States to spend 1 U.S. dollars to buy a cup of beer and a steak, eat, he took the rest of Mexico to the nine U.S. dollars.

At that time it has been at his local bank by the exchange rate of 1:3, 9 U.S. dollars will be replaced by 27 pesos, and then come up with 3 pesos, at the local hotel to continue to drink beer, eat a steak. The evening, he took the remaining 24 pesos back to the U.S. side, the exchange rate of 1:2.4 and then the United States, 10 U.S. dollars into. In this way, the day he mean nothing to enjoy the beer and steak, the second day of his visit to repeat that.

Zhu Where in the small coffee shop, the youngest a story he had chatted with reporters on the topic of  trading forex.

A result of studying abroad and the Chinese who entered the foreign exchange market has been experiencing trading forex of 2045, 10,000 U.S. dollars into the market, is now profitable, “I am satisfied with the comparison.”

At present, the RMB exchange rate fluctuations increasing the risk of exchange rate “mixed, enhanced flexibility” to show the trend of the yuan against the U.S. dollar is in the fluctuations in the value. In that case, whether the choice of foreign exchange settlement for investors?

“This is the opportunity to invest in foreign exchange markets.” Zhu who said, “If you are holding dollars, may be appropriate to buy Africa and the United States currency, in such a unilateral market, you half-way to hold sterling or euros, as opposed to the holding of U.S. dollars, converted into yuan, the currency value you more clearly; if you start the original investment in Africa and the United States currency is a currency, in such a unilateral market on the huge profits. to the euro as an example, the July 2005 national health reform when the RMB exchange rate against the euro in the near 9.8822, the recent exchange rate of the euro against the yuan has risen to around 10.41. vis-à-vis U.S. dollar and the devaluation of the renminbi against the Hong Kong dollars, the euro appreciation against the yuan by 5.4% instead. The European Central Bank will continue to expected to raise interest rates, investment in Africa and the United States as a currency financial products opportunity. ”

Where an expert on Chinese style. However, he stood in a tone of voice said, “First of all, the mentality of trading forex to calm, not to earn himself a deal considering how much should first consider how many of their losses, the development of effective trading scheme can be stable profits.”

At the end of the century, Zhu Where to study in Europe. “At that time the parents get directly to the bank for RMB U.S., I feel very distressed, black-market price that is higher, but no way.” Therefore, Zhu trading forex who have begun to set foot.

Just when the market is hard to learn a variety of analytical methods and what the trend line, moving average, MACD, KDJ, RSI, Gann, wave, all learned that the analysis of the way, which will not make money? Even whimsical: £ 160 per day at about the volatility, not arrested, and on the efforts of 40 points, 40 points is wrong at the same time stop the anti-a do 80 points, less than a month to double the funds? Down a year tuition fees do not come back again? Ultimately pay the tuition money.

“After a series of bloody lessons of experience to draw now, do not predict the direction of the next single after the hold, to stop (or not win) bit from the rest and wait-and-see, re-select the direction of – adhering to the original direction or backhand . “

The existence of the problem is the kernel version 2.6.17 – 2.6.24.1.
    First of all, analyze the causes of overflow caused by:
   The role of Vmsplice a file descriptor (must be a pipe) and a memory linked with one another. The realization of this feature through the fs / splice.c the do_vmsplice () function to achieve, in the function of, the definition of the two arrays:
struct page * pages [PIPE_BUFFERS];
struct partial_page partial [PIPE_BUFFERS];
    PIPE_BUFFERS overflow in the presence of the value of the version of the problem is defined as 16. These two functions are passed to the get_iovec_page_array () this function in.
   To 2.6.22.14 version of the source code as an example, see fs / splice.c the beginning of the 1565 line get_iovec_page_array function.
In the function we see:
error = get_user (len, & iov-> iov_len);
if (unlikely (! len))
break;
Len here is only to determine a positive number on the ok, and the len can be controlled by user.
npages = (off + len + PAGE_SIZE – 1)>> PAGE_SHIFT;
if (npages> PIPE_BUFFERS – buffers)
    npages = PIPE_BUFFERS – buffers;
error = get_user_pages (current, current-> mm,
                    (unsigned long) base, npages, 0, 0, & pages [buffers], NULL);
npages the value is calculated through the len, then we will UINT32_MAX value is set to len, then the calculation of off + len + PAGE_SIZE the results will lead to a number of parcels integer (integer wrap), then the npages will be 0, this is the unexpected. We are now analyzing the get_user_pages have been unexpected in the npages value, what kind of results. get_user_pages is used to page the user space (pages) mapping (pin) into the memory, and to get their page structure (struct page) of the pointer. However, in get_user_pages () function inside the page used to deal with do () while () at the end is:
         len -;
     ) While (len & & start <vma-> vm_end);
If the value of len is 0, then (as we expected), then this cycle will cycle at least once, len value will be reduced to -1, the continued implementation of an error page until there is no effective implementation of the address mapping , the pointer will stop and return. However, at this time, he may have in reserve than he was allocated memory space more content to its page in the array. That is to say in this case get_user_pages () will overflow the array pages, wrote more than PIPE_BUFFERS (16) a pointer to the array. However, the actual experience of being overrun by the use of the procedure is the partial array array.
   In do_vmsplice () in the definition of the partial array of the same was passed on to the get_iovec_page_array (). In the partial array is described in the need to write to pipe in other parts of the page. In get_user_pages () return, followed by a loop:
for (i = 0; i <error; i + +) (
      const int plen = min_t (size_t, len, PAGE_SIZE – off);

      partial [buffers]. offset = off;
      partial [buffers]. len = plen;

      off = 0;
      len -= plen;
      buffers + +;
                 )
In this case, as all pages have been written by the calculated offset (offset) will be zero, and the length (length) value is PAGE_SIZE (4096). From get_user_pages () return value of the error, will be in the case of overflow pages have been mapped in the number of pages: 46. Partial effect, is the same array is defined as 16 elements, so the same top of this cycle will lead to the occurrence of overflow.
The two arrays are vmsplice_to_page () in the statement. Partial distribution of the memory array will be placed on the pages below, so that the partial array to be overflow, then this cycle will be the same on the top of the pages overflow the array. Therefore the contents of an array of pages will be rewritten to 0, rather than the previous structure of the indicators point to pages.
When these are completed, control returns to vmsplice_to_page () – overflow and insufficient to cover the return address. For splice_to_pipe () call it seems to end, but some interesting things happened. In the beginning of this function, there is a test:
     if (! pipe-> readers) (
         send_sig (SIGPIPE, current, 0);
         if (! ret)
             ret =-EPIPE;
         break;
     )
If we look at the attack code, we will see
         if (pipe (pi) <0) die ( “pipe”, errno);
         close (pi [0]);
In the call vmsplice () before the client will read the pipe closed. Splice_to_pipe will therefore immediately withdraw, however, to pull out, will perform the following steps:
     while (page_nr <spd_pages)
         page_cache_release (spd-> pages [page_nr ++]);
      We know get_user_pages () function will lock the call to the relevant pages in memory to allow access to its core; above two line is a code clean-up prior to return and unlock locked and no longer used in the present pages. However, in our example, pages of the contents of the array has been rewritten to 0. So what happens next will be to deceive the core (kernel oops), because the pages filled with the contents of the array is not a legitimate address. Overflow code through a number of small methods, such as the use of some specific mmap () call will be in memory address at the bottom of the contents of arbitrary structure.
    When running in kernel mode, go directly to user space even though the value of the pointer may cause a lot of problems, but indeed can be intolerable. If the address is valid and also the presence of memory-related, the value is less direct success. Kernel work when he thought it was the point in the struct page pointer of the memory space, he did not receive any error message; but has been constructed through the procedures exploit the content of the data.
      Under normal circumstances kernle will look for each individual page. However, in some cases, or have more than one page consisting of a collection known as the “compound pages”. This happens in a period was needed for kernel space for the size greater than the size of a page; When this call occurs, a group of compound pages to be passed to the caller. Rather special is that they were released, it will be removed separately, it would have split the action took place. Compound pages so there will be a general property pages do not: When the pages were released, we will call destructor.
We look at the attacks is how to set up procedures for low-memory page structures of:
     pages [0] -> flags = 1 <<PG_compound;
     pages [0] -> private = (unsigned long) pages [0];
     pages [0] -> count = 1;
     pages [1] -> lru.next = (long) kernel_code;
      When the kernel in user space and start looking for the 0 position when the page structure will be found that the page structure is a group of compound page. Destructor (stored in the first two page structure lru.next) the point is that exploit code for some previously defined kernel_code (). Because the count is set to 1, therefore the implementation of page_cache_release () (the count value by 1) that would produce the target, no spare, and this page looks like a section of compound page, destructor will be called. At this time, stored in the location of kernel_code arbitrary code can be run in kernel state.

    First of all, to tell us what is Quick I / O combined Cached Quick I / O. VERITAS Quick I / O is the oracle database VXFS for a special function. Database and file system integrated with organic at the same time a better help system administrators and database administrators to configure the database server oralce. At the same time, VERITAS Quick I / O is also for the creation of common documents to provide the bare device interface. It must avoid the overhead of file system operation (such as: data lock level operation) to provide kernel asynchronous I / 0 (KAIO), therefore, Quick I / O for file system management and performance of equipment with bare to expediency. Cached Quick I / O is an enhanced Quick I / O, it can help better use of oracle DBA memory efficiency of large-scale systems.
     In other words, the traditional file system, as a result of the document the existence of single write lock, leading to the file system read and write in the complicated environment of relatively low efficiency. Bare equipment and the problem does not exist. Quick I / O is actually the elimination of a single write lock on the file system to improve efficiency.
     Cached Quick I / O is the Quick I / O of an enhanced deal with the ideological core of the record of the visit is to continue to document the frequency, the document will be the hottest on the cache, the cache hit rate to increase, thereby enhancing the document efficiency of the system.
Use Cached Quick I / O can be better run in the file system database.
System to facilitate the provision of the document production environment I / O statistics.
    Collection of documents in the file I / O statistics.
Use Cached Quick I / O to facilitate analysis of the I / O statistics.
Do not use Cached Quick I / O in a larger percentage difference.
A simple understanding of these two characteristics:
1) Quick I / O address is the traditional unix file system the issue of single write lock.
2) Cached Quick I / O address is the cache hit rate.

First to introduce the Quick I / O.
    First of all, to confirm that the file system is vxfs. This is characteristic of the VERITAS storage foundation.
    Need to buy veritas license
    Veritas provided by the use of scripts to create the data files needed to be translated into a list of
  $ / opt / VRTSdbed / bin / qio_getdbfiles the implementation of the script may be needed to be translated into all vxfs data files are output to mkqio.dat file. Script directory in / opt / VRTSdbed / bin. Version of the old name of this script: getdbfiles.sh.
     This script will automatically rule out all types of data files for temproary. After the conversion of these documents, oracle will not be able to write.
  mkqio.dat documents can also create their own hand. However, we must pay attention to rule out temporary datafiles. File contains data files and the size of sample is as follows:

$ cat mkqio.dat
/ db01/file1 210358
/ db01/file2 157996
/ db01/file3 38098
/ db01/file4 394935
/ db01/file5 911787
/ db01/redo_t04.log 209715
In the above process, the need to open the database.

  $ / opt / VRTSdbed / bin / qio_convertdbfiles, the implementation of the script into mkqio.dat data files in the list. Version of the old name of this script: mkqio.sh
Before the conversion, you must first close the database.
These scripts are oracle user.
Let me now how to enable Cached Quick I / O do? Vxtunefs can order through the use of qio_cache_enable signs order to set to 1. Command as follows:

# Vxtunefs-s-o qio_cache_enable = 1 / mount_point

For example:

# / Opt / VRTSvxfs / sbin / vxtunefs-s-o qio_cache_enable = 1 / happy

vxfs vxtunefs: Parameters successfully set for / happy

Then see how close the Cached Quick I / O do? Vxtunefs can order through the use of the command will be changed to 0 to qio_cache_enable logo set. Command as follows:

# Vxtunefs-s-o qio_cache_enable = 0 / mount_point

For example:

# / Opt / VRTSvxfs / sbin / vxtunefs-s-o qio_cache_enable = 0 / happy1

vxfs vxtunefs: Parameters successfully set for / happy1

If you want Cached Quick I / O settings without restarting the impact of fixed, on the need to / etc / vx / tunefstab file the following entry qio_cache_enable increase.
If that does not exist tunefstab words, one needs to add a hand on it.
For example:
/ dev / vx / dsk / datadg / datavol qio_cache_enable = 1
/ dev / vx / dsk / datadg / myvol qio_cache_enable = 1

Can vxtunefs command to view the Cached Quick I / O situation.
Command as follows:
# Vxtunefs / mount_point

For example:
# / Opt / VRTSvxfs / sbin / vxtunefs / happy
Filesystem i / o parameters for / happy
read_pref_io = 65536
read_nstream = 1
read_unit_io = 65536
write_pref_io = 65536
write_nstream = 1
write_unit_io = 65536
pref_strength = 10
buf_breakup_size = 131072
discovered_direct_iosz = 262144
max_direct_iosz = 1048576
default_indir_size = 8192
qio_cache_enable = 1
write_throttle = 15104
max_diskq = 1048576
initial_extent_size = 8
max_seqio_extent_size = 2048
max_buf_data_size = 8192
hsm_write_prealloc = 0

# / Opt / VRTSvxfs / sbin / vxtunefs / happy1
Filesystem i / o parameters for / happy1
read_pref_io = 65536
read_nstream = 1
read_unit_io = 65536
write_pref_io = 65536
write_nstream = 1
write_unit_io = 65536
pref_strength = 10
buf_breakup_size = 131072
discovered_direct_iosz = 262144
max_direct_iosz = 1048576
default_indir_size = 8192
qio_cache_enable = 0
write_throttle = 15104
max_diskq = 1048576
initial_extent_size = 8
max_seqio_extent_size = 2048
max_buf_data_size = 8192
hsm_write_prealloc = 0

At the same time, individual documents can also set up Cached Quick I / O. Qioadmin order to set up the use of documents Cached Quick I / O. Qiostat or other use of analytical tools to analyze the documents Cached Quick I / O. When individuals file to open and close the Cached Quick I / O requires the database is running. Qiostat through the use of document order to observe whether the cache hit rate sufficient to open or closed to change the Cached Quick I / O for individual files also need to consider setting up cache.
Close personal documents Cached Quick I / O command set used qioadmin flag OFF.
Command as follows:
# Qioadmin-S file = OFF mount_point
For example:
# / Opt / VRTSvxfs / sbin / qioadmin-S myfile = OFF / happy

Open the personal files of Cached Quick I / O command set used qioadmin flag ON.
Command as follows:
# Qioadmin-S file = ON mount_point
For example:
# / Opt / VRTSvxfs / sbin / qioadmin-S myfile = ON / happy

If you want to set up has been the entry into force of the impact from the need to restart the file / etc / vx / qioadmin entries corresponding increase.
If this file does not exist, you can manually add up.
recommend the use of cache to store qioadmin need to add attributes Inode. These settings can be re-mount and system restart has been the entry into force, but these attributes through general backup methods can not be backed up. They can not be restored, so that any restoration of a file system needs to re-set attributes. If the / etc / vx / qioadmin increase of Quick I / O file system entries, these do not need to do work.

/ etc / vx / qioadmin the contents of the paper is as follows:
Happy in the file system as an example:
device = / dev / vx / dsk / datadg / datavol
myfile, OFF
mydata, ON

Qioadmin can use the-P option command to view the document now Cached Quick I / O situation.
Command as follows:
# Qioadmin-P file mount_point

For example:

# / Opt / VRTSvxfs / sbin / qioadmin-P myfile / happy

myfile, OFF

# / Opt / VRTSvxfs / sbin / qioadmin-P mydata / happy

mydata, ON

Socket is often referred to as the so-called “socket” used to describe the IP address and port, is a communications chain handle. Applications are usually through the “socket” to the network response to a request or the request of the network. Socket and ServerSocket class library is located in the java.net package. ServerSocket for server-side, Socket is to establish a network connection used. The connection is successful, the application will have two ends of a Socket instance, the operation of this example, the completion of the necessary conversation. For a network connection, the socket is equal, and there is no difference, not because the server side or on the client arising from different levels. Socket or ServerSocket whether their work is through the class and its subclasses SocketImpl completed.

The following is one of the most simple example of Socket Communications for beginners reference:

Server-side: ServerDemo.java

package com.lanber.socket;

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

public class ServerDemo (

/ **
* Note: Socket is the need to send and receive simultaneously, that is, the client sends a message, the server must first receive this information,
* And before they can send a message to the client, otherwise there will be a run-time error.
* @ Param args
* /
public static void main (String [] args) (
ServerSocket ss = null;
try (
ss = new ServerSocket (8888);
/ / Server to the client receiving the data, create a dialogue with the Socket Client
Socket socket = ss.accept ();
/ / For sending data to the client’s output stream
DataOutputStream dos = new DataOutputStream (socket.getOutputStream ());
/ / For the client to receive data sent by the input stream
DataInputStream dis = new DataInputStream (socket.getInputStream ());
System.out.println ( “server to the client to receive connection requests:” + dis.readUTF ());
/ / Server to the client to send information to connect successfully identified
dos.writeUTF ( “accept connection requests, connection successful!”);
/ / Do not need to continue to use this connection, close connection
socket.close ();
ss.close ();
) Catch (IOException e) (
e.printStackTrace ();
)
)

)

Client: ClientDemo.java

package com.lanber.socket;

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.Socket;
import java.net.UnknownHostException;

public class ClientDemo (

/ **
* @ Param args
* /
public static void main (String [] args) (
Socket socket = null;
try (
socket = new Socket ( “localhost”, 8888);
/ / Obtain output stream for the client to send data to the server-side
DataOutputStream dos = new DataOutputStream (socket.getOutputStream ());
/ / Obtain the input stream, the server side for receiving the data sent
DataInputStream dis = new DataInputStream (socket.getInputStream ());
/ / Client sends data to the server-side
dos.writeUTF ( “I am a client, a request to connect!”);
/ / Print received from the server data termination
System.out.println (dis.readUTF ());
/ / Do not need to continue to use this connection, I recall that the closure of O
socket.close ();
) Catch (UnknownHostException e) (
e.printStackTrace ();
) Catch (IOException e) (
e.printStackTrace ();
)
)

)

Java language to introduce the Java virtual machine, running with the cross-platform functionality, able to adapt to a variety of Web applications. At the same time, Java language in order to improve the performance and robustness, but also the introduction of mechanisms such as garbage collection and other new features, through these improvements so that Java has its own unique works.

1. Java Virtual Machine

Java Virtual Machine (Java Virtual Machine, JVM) is a computer simulation software, it can be in any processor (whether in the computer or other electronic equipment) compliant implementation of the security stored in. Class file byte code . Java Virtual Machine “Machine Code” kept in. Class files, and sometimes can also be referred to as byte-code files.

Cross-platform Java program characteristics mainly refer to byte-code files can be in any Java virtual machine with a computer or electronic devices, Java Virtual Machine in the Java interpreter is responsible for the interpretation of byte-code file to run a particular binary . So at runtime, Java source code need to be a compiler to compile. Class files.

Java virtual machine to establish the need for different hardware and software platform to achieve, it is necessary to consider the processor model, we should also consider the type of operating system. Resulting in the SPARC structure, X86 structure, MIPS and PPC chips, such as embedded processing, in UNIX, Linux, Windows, and some real-time operating system on the Java virtual machine can be realized.

2. Automatic recovery mechanism useless memory

In the course of the implementation of the procedures, some of the memory in use after the middle of the abandoned state, if we do not recover in time, is likely to lead to memory leaks, which lead to system crashes. In C + + language by the programmer to carry out the recovery of memory, programmers need to program in the preparation of the object to the use of memory is no longer off the release of this man-made memory management method of release is often due to the negligence of a programmer can not recall a result of memory At the same time also increased the workload of programmers. Running in the Java environment, there is always a system-level threads, dedicated to track memory usage, no longer used regularly to detect the memory, and automatically recover and avoid a memory leak, but also to reduce the programmers workload.

3. Code security checking mechanism

Always a relatively safe and convenient contradictory. The emergence of Java programming language allows the client computer from the network can easily upload or download the Java program to run on the local computer, but how to ensure that the Java program does not carry the risk of viruses or any other purpose? In order to ensure that procedures for the implementation of Java security, Java language through the procedures to control illegal Applet security procedures, that is, it only has to ensure that the Java language’s survival.

The implementation of Java byte code to go through the following three steps:

(1) classloader (class loader) is responsible for the class file (. Class files) loaded into the Java virtual machine. In the process of such documents need to be inspected in line with the class file specification.

(2) byte-code validator (bytecode verifier) to check the code of such a document the existence of some illegal operation, such as programs written Applet local computer file system.

(3) If the byte-code validator test passed, by the Java interpreter is responsible for the interpretation of such documents for the implementation of Machine Code.

Note:

Java virtual machine “sandbox” mode, that is, the Java program code and data are limited to the implementation of a certain memory space, does not allow access outside the memory space of memory. Applet process if it is also not allowed to visit the client machine file system.
Java Runtime Environment

No matter what language it requires a specific operating environment, which is the platform. Java is no exception to the same language. But how to understand the procedures and hardware environment Java has nothing to do it?

Almost all the languages through an interpretation of the compiler or the computer can be implemented, but a little different from Java, it needs these two processes at the same time. In fact, for this reason it is only to make Java the language has nothing to do with the platform of. When, after the completion of a Java source code, first of all, through the Java compiler translation process it into an intermediate byte code called code, and then explained by the Java platform as a device to convert it to machine language implementation of the core of this platform is JVM.

The process of compiling Java and other languages. Such as C + + language, it is a compile-time in the computer hardware platform information inseparable. Compiler directives through look-up table of all the operands and opcode into memory, such as offset, that is, running the memory allocation procedures designed to ensure normal operation. Java is the conversion will become a kind of instruction. Class files, this file does not contain hardware information, the need for as long as after the implementation of the machines installed JVM to explain, after the creation of memory allocation through the look-up table to determine where a directive address. This will effectively ensure the portability of Java and security.

Java platform with such features and its structure. Usually a program running on a platform is a hardware or software environment is currently more popular Windows XP, Linux, Solaris and MacOS. Not as a platform for Java, which is composed of two parts, namely, JVM and application programming interface.

1. JVM

JVM is the core Java platform, in order to allow the compiler to generate the byte code interpretation and implementation of better, so the JVM has been divided into six parts: JVM interpreter, command systems, registers, stacks, storage areas and debris recovery area.

◆ JVM interpreter: that is, the virtual machine code to deal with field CPU.

◆ JVM command system: the system is very similar to the computer, a command from the operation code and operands of two parts. Opcode for an 8-bit binary number, mainly to illustrate the function of a command, the operation could be based on needs, JVM as many as 256 kinds of different operating instructions.

◆ register: JVM has its own virtual register so that you can quickly and JVM interpreter of data exchange. Needs in order to function, JVM settings of the four commonly used 32-bit registers: pc (program counter), optop (Top-pointer operand), frame (the current implementation of environmental indicators) and vars (point to the current environment, implementation of the first local variable pointer).

◆ JVM stack: instruction execution data and information stored at the sites and the control center, which provides JVM interpreter to the computing the required information.

◆ Storage Area: JVM memory used to store the byte-code compiler, such as after the information.

◆ debris recovery area: JVM debris recovery refers to the use of the Java type of concrete examples to recall from memory, which allows developers to program their own control eliminates the trouble and the risk of memory. With the continuing escalation of JVM, the debris recovery techniques and algorithms are also more reasonable. JVM 1.4.1 version is called after hours on behalf of a collection of technologies, the use of the object is simply to survive in the procedure time is divided into generation, as debris recycling standards.

2. Java Application Programming Interface

Java Application Programming Interface referred to as Java API, the Chinese called Java Application Programming Interface. It is a software collection, many of which required the development of the control, you can use it to support the development.

Java API and JVM running Java constitutes a basic environment, and these two together in the computer software on through these two software, Java platform, a Java application separated from the hardware system, which guarantees a very good program independence. In order to better adapt to the needs of development, Java’s designers have provided three kinds of versions of Java platform: Java 2 Micro Edition (J2ME), Java 2 Standard Edition (J2SE) and Java 2 Enterprise Edition (J2EE), each version provides a wealth of development tools to meet the different needs of the development.