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Example — Reading a URL

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Overview Description of URLdemo Running the Example

Overview

This program, URLdemo, opens a connection to a Web site specified by a URL (Uniform Resource Locator) for the purpose of reading text from a file at that site.

URLdemo constructs an object of the Sun Java API class, java.net.URL, which enables convenient handling of URLs. Then, it calls a method on the URL object, to open a connection.

To read and display the lines of text at the site, URLdemo uses classes from the Java I/O package java.io. It creates an InputStreamReader object, and then uses that object to construct a BufferedReader object. Finally, it calls a method on the BufferedReader object to read the specified number of lines from the site.

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Description of URLdemo

The major tasks performed by URLdemo are:

1. Construct a URL object.

   The example first calls a constructor on java.net.URL and assigns the resulting object to variable url. The URL constructor takes a single argument, the name of the URL to be accessed, as a string. The constructor checks whether the input URL has a valid form.

   url = java.net.URL(... 
   'http://www.mathworks.com/support/tech-notes/1100/1109.html')

2. Open a connection to the URL.

   The second statement of the example calls the method, openStream, on the URL object url, to establish a connection with the Web site named by the object. The method returns an InputStream object to variable, is, for reading bytes from the site.

   is = openStream(url);

3. Set up a buffered stream reader.

   The next two lines create a buffered stream reader for characters. The java.io.InputStreamReader constructor is called with the input stream is, to return to variable isr an object that can read characters. Then, the java.io.BufferedReader constructor is called with isr, to return a BufferedReader object to variable br. A buffered reader provides for efficient reading of characters, arrays, and lines.

   isr = java.io.InputStreamReader(is);
   br = java.io.BufferedReader(isr);

4. Read and display lines of text.

   The final statements read the initial lines of HTML text from the site, displaying only the first 4 lines that contain meaningful text. Within the MATLAB for statements, the BufferedReader method readLine reads each line of text (terminated by a return and/or line feed character) from the site.

   for k = 1:288           % Skip initial HTML formatting lines
      s = readLine(br);
   end
   
   for k = 1:4             % Read the first 4 lines of text
      s = readLine(br);
      disp(s)
   end

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Running the Example

When you run this example, you see output similar to the following. (Note that the line breaks were changed to fit the output in the documentation).

<p>This technical note provides an introduction to vectorization
techniques. In order to understand some of the possible techniques,
an introduction to MATLAB referencing is provided. Then several 
vectorization examples are discussed.</p> 
<p>This technical note examines how to identify situations where 
vectorized techniques would yield a quicker or cleaner algorithm.
Vectorization is ofen a smooth process; however, in many 
application-specific cases, it can be difficult to construct a 
vectorized routine. Understanding the tools and

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Introduction to Programming Examples

Example — Finding an Internet Protocol Address

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