Java Advanced Learning (iii) IO basics

The most important function of a computer is to process data. A useful computer language needs to have good IO capabilities to allow the unhandled data to flow into the program and let the processed data flow out.

Java's IO functionality is complex compared to other languages. In other languages, many IO functions, such as reading files, are encapsulated and can be implemented in one or two-line programs. In Java, programmers often need multiple levels of decoration (decoration) in order to achieve file reading.

The advantage of relative complexity is the flexibility of IO. In Java, programmers can control the entire process of IO to design the best IO approach. We will see more in the following sections.

IO Example

Here is the file I used to demonstrate file.txt

Hello world!

Hello nerd!

Let's look at an example of a file read:

Import java.io.*;   
       
public class Test   
{public   
    static void Main (string[] args)   
    {   
        try {   
            BufferedReader br =   
              New BufferedReader (New FileReader ("file.txt"));    
       
            String line = Br.readline ();   
       
            While [line!= null] {   
                System.out.println (line);   
                line = Br.readline ();   
            }   
            Br.close ();   
        }   
        catch (IOException e) {   
            System.out.println ("IO Problem");}}   

This program contains a try...catch...finally exception handler.

Adorners and functional combinations

The key to program IO is to create BufferedReader object BR:

BufferedReader br = new BufferedReader (New FileReader ("file.txt"));

In the process of creation, we first set up a FileReader object that is capable of reading a byte stream from the file "file.txt" and converting it to a text stream. In Java, the standard text encoding is Unicode. BufferedReader () receives the FileReader object, expands the FileReader function, and creates a new BufferedReader object. This object provides cache read (buffered) functionality in addition to the ability to read and transform the files above. Finally, by invoking the ReadLine () method on the BR object, we can read the file line by row.

(cache reads are a cache of areas in memory that store FileReader-read text streams.) When the contents of the cache are read (such as the ReadLine () command), the cache loads subsequent text streams. )

BufferedReader () is an adorner (decorator) that receives an original object and returns a decorated, functionally complex object. The advantage of a decorator is that it can be used to decorate different objects. What we are modifying here is the stream of text read from the file. Other text streams, such as standard input, stream traffic, and so on, can be BufferedReader () to enable cache reading.

The following figure shows how BR works, and the data flows from the bottom up:

(text flow can refer to Linux text Stream and TCP protocol and stream communication)

The above decoration process is similar to the text stream idea in Linux. In Linux, we use similar functions to process and deliver text streams. In Java, we use adorners. But their purpose is similar, is to realize the function of modularity and free combination.

See more highlights of this column: http://www.bianceng.cnhttp://www.bianceng.cn/Programming/Java/