More string operations

More string operations

• Converting strings:

     public String toLowerCase()
     public String toUpperCase()
      

  Demo 2. A case-insensitive word counter/finder differs from the above code only by the added two lines in the following.

    private int substringCounter( String text, String word)
    {
          int count = 0;
          int pos;
          
          text = text.toLowerCase();
          word = word.toLowerCase();
          
          pos = text.indexOf(word,0);
          
          while ( pos >= 0 )
          {
              count++;
              pos = text.indexOf(word,pos+word.length());
          
          }
          return count;
    }
      

  Note that the assignment statements to text and word are required. String methods do not manipulate the given string. They make a brand new one.

• Cutting and pasting strings
  • To paste together two strings, use "+"
  • To cut (i.e., to extract a substring of a string) use:

       public String substring(int startIndex, int indexBeyond)
    

    For example:

        String ratingText = "Rated PG-13";
        String rating;
        rating = ratingText.substring(6, 11);
    

  Demo 3. Link finder:

  We want to write a program to find and extract all of the links in an html file. See FindLinks.

  To do this, we need to know how a link is defined in an HTML file:

      <a href="the URL">link </a>
  

  So we need to find the tags "<a>" and "</a>" that surround the URL.

  Convert the string that is the HTML file to lowercase.

     String links = "";
  

  Find the first position of "<a"

  While there is a link remaining (i.e., position is not -1)

  • Find the other end of it i.e., ">"
  • Get the substring between those (that's the URL)
  • Concatenate it to links found so far
  • Find the next "<a"

          // Extract all the links from a web page
    private String findLinks( String fullpage )
    {                     
                          
        int tagPos,               // Start of <A tag specification
            tagEnd;               // Position of first ">" after tag start
                  
                  // A lower case only version of the page for searching
        String lowerpage = fullpage.toLowerCase();
        
                  // Text of one A tag
        String tag;
        
                  // The A tags found so far
        String links = ""; 
        
                  // Paste stuff on end of page to ensure searches succeed
        fullpage = fullpage + " >";
    
        tagPos = lowerpage.indexOf("<a ",0);
      
        while (tagPos >= 0 ) {
           tagEnd = fullpage.indexOf(">",tagPos+1);            
           tag = fullpage.substring(tagPos, tagEnd+1);
           links = links + tag + "\n";                    
           tagPos = lowerpage.indexOf("<a ", tagEnd);             
        }         
          
        return links;
    }
  

More string operations