Some useful String methods

Some useful String methods

The demo program StringDemo

• public int length()
  returns the length of a string.

     String courseName = "Data Structures";
     int nameLength = courseName.length();
  

  nameLength gets the value 15.

• public int indexOf(String s)
  returns the starting index of the first occurrence of string s; returns -1 if s was not found.

     courseName.indexOf("S") 
  

  returns the value 5. Note that indexing starts at 0, as it does with arrays.

  Of course, we can also say

     String searchString = "S";
  

  and then

      courseName.indexOf(searchString)
  

  Another option is:

     public int indexOf(String s, int startIndex)
  

  which begins its search at the specified index.

  What's the result of

      courseName.indexOf("Struct", 2)
      courseName.indexOf("Struct", 8)
      courseName.indexOf("s", 2)
      courseName.indexOf("s", 6)
  

  Here is a method that searches for the number of occurrences of a string, word, in another string, text. document.

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

  Recall from above that "s" and "S" are different strings.

• 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.

Some useful String methods