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()
      

  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