Manipulating Characters in a String

The String class has a number of methods for examining the contents of strings, finding characters or substrings within a string, changing case, and other tasks.


Getting Characters and Substrings by Index
You can get the character at a particular index within a string by invoking the charAt() accessor method. The index of the first character is 0, while the index of the last character is length()-1. For example, the following code gets the character at index 9 in a string:

String anotherPalindrome = "Niagara. O roar again!";
char aChar = anotherPalindrome.charAt(9);

Indices begin at 0, so the character at index 9 is 'O', as illustrated in the following figure:

If you want to get more than one consecutive character from a string, you can use the substring method. The substring method has two versions, as shown in the following table:

The following code gets from the Niagara palindrome the substring that extends from index 11 up to, but not including, index 15, which is the word "roar":

String anotherPalindrome = "Niagara. O roar again!";
String roar = anotherPalindrome.substring(11, 15); 

Other Methods for Manipulating Strings

Here are several other String methods for manipulating strings:

Searching for Characters and Substrings in a String

Here are some other String methods for finding characters or substrings within a string. The String class provides accessor methods that return the position within the string of a specific character or substring: indexOf() and lastIndexOf(). The indexOf() methods search forward from the beginning of the string, and the lastIndexOf() methods search backward from the end of the string. If a character or substring is not found, indexOf() and lastIndexOf() return -1.

The String class also provides a search method, contains, that returns true if the string contains a particular character sequence. Use this method when you only need to know that the string contains a character sequence, but the precise location isn't important.

The following table describes the various string search methods.

Replacing Characters and Substrings into a String

The String class has very few methods for inserting characters or substrings into a string. In general, they are not needed: You can create a new string by concatenation of substrings you have removed from a string with the substring that you want to insert.

The String class does have four methods for replacing found characters or substrings, however. They are:

Comparing Strings and Portions of Strings

The String class has a number of methods for comparing strings and portions of strings. The following table lists these methods.

The following program, RegionMatchesDemo, uses the regionMatches method to search for a string within another string:

public class RegionMatchesDemo
{
  public static void main(String[] args)
   {
    String searchMe = "Green Eggs and Ham";
    String findMe = "Eggs";
    int searchMeLength = searchMe.length();
    int findMeLength = findMe.length();
    boolean foundIt = false;
    for (int i = 0; i <= (searchMeLength - findMeLength); i++)
      {
        if (searchMe.regionMatches(i, findMe, 0, findMeLength))
          {
             foundIt = true;
             System.out.println(searchMe.substring(i, i + findMeLength));
             break;
         }
    }
   if (!foundIt) System.out.println("No match found.");
  }
}
The output from this program is: Eggs.

The program steps through the string referred to by searchMe one character at a time. For each character, the program calls the regionMatches method to determine whether the substring beginning with the current character matches the string the program is looking for.

Unicode

Each keyboard character has a numeric equivalent. It is possible to find the number that represents a key by using (int).  It is also possible to do the reverse by using (char)

The following code demonstrates the use of (int) and (char):

import java.util.*;
public class Unicode
{

Scanner in = new Scanner(System.in);

void unicode_to_char()
{
int num;
System.out.print("Enter a number from 0 to 255: ");
num = in.nextInt();
System.out.println(num + " represents the character '" + (char)(num) + "'.");
}


void char_to_unicode()
{
char inputItem;
String text;
System.out.print("Enter a single character: ");
text = in.next();
inputItem = text.charAt(0);
if(Character.isLetter(inputItem))
System.out.println("The letter '" + inputItem + "' is " + (int)(inputItem) + " in unicode.");
else if(Character.isDigit(inputItem))
System.out.println("The digit '" + inputItem + "' is " + (int)(inputItem) + " in unicode.");
else if(Character.isWhitespace(inputItem))
System.out.println("That character(Space, Tab, Enter) is " + (int)(inputItem) + " in unicode.");
else
System.out.println("The character '" + inputItem + "' is " + (int)(inputItem) + " in unicode.");

}
}

The follow chart shows the unicode values for many of the characters:

For each of the Programming 1 lessons you are strongly encouraged to view and play around with the sample code provided in the BlueJ Java Student Samples folder.

Open BlueJ and choose Open Project from the Project menu. Navigate to your Programming 1 folder on the I: drive and open the BlueJ Java Student Samples folder. Open the project named Strings.

Lesson Example: Project Strings, Class StringManipulation, methods A_toLowerCase_String(), B_toUpperCase_String(), C_length_String(), D_trim_String(), E_startsWith_String(), F_endsWith_String(), G_compareTo_String(), H_compareToIgnoreCase_String(), I_equals_String(), J_equalsIgnoreCase_String(), K_concat_String(), L_replaceAll_String(), M_replace_String(), N_charAt_String(), O_indexOf_String(), P_anyIndexOf_String(), Q_lastIndexOf_String(), R_substring_Start_And_End_String() and S_substring_Start_To_End_String()

• Right-click on the Class named StringManipulations select new StringManipulations()
• Right-click on the red rectangle and choose the method named A_toLowerCase_String()
• Right-click on the red rectangle and choose the method named B_toUpperCase_String()
• Right-click on the red rectangle and choose the method named C_length_String()
• Right-click on the red rectangle and choose the method named D_trim_String()
• Right-click on the red rectangle and choose the method named E_startsWith_String()
• Right-click on the red rectangle and choose the method named F_endsWith_String()
• Right-click on the red rectangle and choose the method named G_compareTo_String()
• Right-click on the red rectangle and choose the method named H_compareToIgnoreCase_String()
• Right-click on the red rectangle and choose the method named I_equals_String()
• Right-click on the red rectangle and choose the method named J_equalsIgnoreCase_String()
• Right-click on the red rectangle and choose the method named K_concat_String()
• Right-click on the red rectangle and choose the method named L_replaceAll_String()
• Right-click on the red rectangle and choose the method named M_replace_String()
• Right-click on the red rectangle and choose the method named N_charAt_String()
• Right-click on the red rectangle and choose the method named O_indexOf_String()
• Right-click on the red rectangle and choose the method named P_anyIndexOf_String()
• Right-click on the red rectangle and choose the method named Q_lastIndexOf_String()
• Right-click on the red rectangle and choose the method named R_substring_Start_And_End_String()
• Right-click on the red rectangle and choose the method named S_substring_Start_To_End_String()

Code for method A_toLowerCase_String():

void A_toLowerCase_String()//converts String to all lowercase letters
    {
     String text;
     System.out.print("Enter a word or phrase that uses upper case letters: ");
     text = in.nextLine();
     System.out.println("In lower case that looks like: " + text.toLowerCase());
    }
 
Code for method B_toUpperCase_String():   
   
void B_toUpperCase_String()//converts String to all uppercase letters
    {
     String text;
     System.out.print("Enter a word or phrase that uses lower case letters: ");
     text = in.nextLine();
     System.out.println("In upper case that looks like: " + text.toUpperCase());
    }
 
Code for method C_length_String():    
 
void C_length_String()//finds the length of a String
    {
     String text;
     int textLength;
     System.out.print("Enter a word or phrase: ");
     text = in.nextLine();
     textLength = text.length();
     System.out.println("The length of " + text + " is " + textLength);
    }
 
Code for method D_trim_String():  
   
void D_trim_String()//removes spaces before and after a String (but not inside the String)
    {
     String text;
     System.out.print("Enter a word or phrase that has spaces before and/or after: ");
     text = in.nextLine();
     System.out.println("The text with spaces before and after removed looks like: " + text.trim()); 
    }
 
 
Code for method E_startsWith_String():     
 
void E_startsWith_String()//compares the start of a String with another String to see if they match
    {
     String text;
     System.out.print("Enter the word 'pizza': ");
     text = in.next();in.nextLine();
     if(text.startsWith("piz"))
     {
      System.out.println("I think you wrote pizza because the first three letters are correct ");
      System.out.println("but you might have entered pizzaz or some other word that starts with 'piz'.");
    }
    else
    System.out.println("The word you entered does not start with piz.");
} 
   
Code for method F_endsWith_String():     
   
void F_endsWith_String()//compares the end of a String with another String to see if they match
    {
     String text;
     System.out.print("Enter the word 'helicopter': ");
     text = in.next();in.nextLine();
     if(text.endsWith("copter"))
     {
      System.out.println("I think you wrote helicopter because the last six letters are correct ");
      System.out.println("but you might have entered 'gyrocopter' or some other word that ends with 'copter'.");
    }
    else
     System.out.println("The word you entered does not end with copter.");
    }   
   
Code for method G_compareTo_String():     
   
void G_compareTo_String()//compares two Strings alphabetically - is case sensitive
    {
     String firstWord,secondWord;
     System.out.print("Enter a word: ");
     firstWord = in.next();in.nextLine();
     System.out.print("Enter another word: ");
     secondWord = in.next();in.nextLine();
    
     if(firstWord.compareTo(secondWord)< 0)
       System.out.println(firstWord + " comes before " + secondWord + " alphabetically.");
     else if (firstWord.compareTo(secondWord)> 0)
       System.out.println(firstWord + " comes after " + secondWord + " alphabetically.");
     else if(firstWord.compareTo(secondWord)== 0)// also works: if(firstWord.equals(secondWord))
       System.out.println(firstWord + " and " + secondWord + " are the same.");
    }  
   
Code for method H_compareToIgnoreCase_String():     
   
void H_compareToIgnoreCase_String()//compares two Strings alphabetically - is not case sensitive
    {
     String firstWord,secondWord;
     System.out.print("Enter a word using lowercase letters: ");
     firstWord = in.next();in.nextLine();
     System.out.print("Enter the same word using uppercase letters: ");
     secondWord = in.next();in.nextLine();
     if(firstWord.compareToIgnoreCase(secondWord)== 0)
       System.out.println(firstWord + " and " + secondWord + " are the same.");
     else
       System.out.println(firstWord + " and " + secondWord + " are not the same.");
    }  
   
Code for method I_equals_String():     
   
void I_equals_String()//compares two Strings to see if they are spelled indentically - is case sensitive
    {
     String firstWord,secondWord;
     System.out.print("Enter a word: ");
     firstWord = in.next();in.nextLine();
     System.out.print("Enter another word: ");
     secondWord = in.next();in.nextLine();
    
     if(firstWord.equals(secondWord))
       System.out.println(firstWord + " and " + secondWord + " are identical.");
     else
       System.out.println(firstWord + " and " + secondWord + " are not identical.");
    
    }  
   
Code for method J_equalsIgnoreCase_String():     
   
 void J_equalsIgnoreCase_String()//compares two Strings to see if they are spelled the same - is not case sensitive
    {
     String firstWord,secondWord;
     System.out.print("Enter a word using lowercase letters: ");
     firstWord =in.next();in.nextLine();
     System.out.print("Enter the same word using uppercase letters: ");
     secondWord = in.next();in.nextLine();
    
     if(firstWord.equalsIgnoreCase(secondWord))
       System.out.println(firstWord + " and " + secondWord + " are spelled the same.");
     else
       System.out.println(firstWord + " and " + secondWord + " are not spelled the same.");
    }  

Code for method K_concat_String():     
   
void K_concat_String()//attaches Srtings together
    {
     String firstWord,secondWord,bothWords;
     System.out.print("Enter a word: ");
     firstWord = in.next();in.nextLine();
     System.out.print("Enter another word: ");
     secondWord = in.next();in.nextLine();
     bothWords = firstWord.concat(secondWord);
     System.out.println("The two words put together are: " + bothWords);
    }   
   
Code for method L_replaceAll_String():    
   
void L_replaceAll_String()//replaces all occurrences of a String within another String, even individual letters
    {
       String text,wrd,rplc;
       System.out.print("Enter a phrase: ");
        text = in.nextLine();
         System.out.print("Enter a word to be replaced in the phrase: ");
     wrd =in.next();in.nextLine();
        System.out.print("Enter the replacement word: ");
        rplc = in.next();in.nextLine();
        System.out.println("The new phrase is: " + text.replaceAll(wrd,rplc));
    }
   
Code for method M_replace_String():  
   
void M_replace_String()//replaces only individual letters in a String
    {
     String text;
     char letterToReplace; //notice the use of char because you can only replace a char not a String
     char replacementLetter; //notice the use of char because you can only replace a char not a String
     String letter1;
     String letter2;
     System.out.print("Enter a word or phrase: ");
     text = in.nextLine();
     System.out.print("Enter a letter to replace in the text entered: ");
     letter1 = in.next();in.nextLine();
     System.out.print("Enter a letter to use as a replacement: ");
     letter2 = in.next();in.nextLine();
     letterToReplace=letter1.charAt(0); //notice conversion of a String to a char
     replacementLetter=letter2.charAt(0); //notice conversion of a String to a char
     System.out.println("Replacing " + letterToReplace + " with " + replacementLetter + " gives: " + text.replace(letterToReplace,replacementLetter));  
    }
      
Code for method N_charAt_String():     
   
void N_charAt_String()//finds the character in a String at a given position
    {
     String text="";
     int position=0;
     char found_char;
     System.out.print("Enter a word or phrase: ");
     text = in.nextLine();
     System.out.print("Enter a number within the length of the entered text: ");
     position = in.nextInt();in.nextLine();
     if (position >=0 & position <= text.length())
     {
      found_char=text.charAt(position);
      System.out.println("Starting with the first character as 0, the character in that position is: " + found_char);
     }
     else
      System.out.println("That number is out of range.");
    }
  
Code for method O_indexOf_String():     
   
void O_indexOf_String()//finds the numeric position of the first occurrence of String within a String
    {
      String text;
      String letter;
      int position;
      System.out.print("Enter a word or phrase: ");  // try cheeseburger
      text = in.nextLine();
      System.out.print("Enter a letter or group of letters found in the word or phrase you entered: "); // enter e
      letter = in.next();in.nextLine();
      position = text.indexOf(letter);
      System.out.println("The first occurrence of " + letter + " is found at position " + position);
    }

Code for method P_anyIndexOf_String():     
   
void P_anyIndexOf_String()//finds the numeric position of the first occurrence of a String within a String from a given position
    {
      String text;
      int position,start_pos;
      System.out.print("Enter a word or phrase that uses the letter 'e' multiple times: ");  // try cheeseburger
      text = in.nextLine();
      System.out.print("Enter a position from where searching for an 'e' will begin: "); // enter e
      start_pos = in.nextInt();in.nextLine();
      position = text.indexOf("e",start_pos);
      System.out.println("The first occurrence of the letter 'e' after the starting position entered is found at " + position);
    }  
   
Code for method Q_lastIndexOf_String():     
   
void Q_lastIndexOf_String()//finds the numeric position last occurrence of a String within a String
    {
      String text;
      String letter;
      int position;
      System.out.print("Enter a word or phrase: ");  // try cheeseburger
      text = in.nextLine();
      System.out.print("Enter a letter or group of letters found in the word or phrase you entered: "); // enter e
      letter = in.next();in.nextLine();
      position = text.lastIndexOf(letter);
      System.out.println("The last occurrence of " + letter + " is found at position " + position);
    }
     
Code for method R_substring_Start_And_End_String(): 

void R_substring_Start_And_End_String()//returns a part of a String starting from a given position and ending at another given position
    {
     String text;
     String theSubstring;
     int positionToStart;
     int positionToEnd;
     System.out.print("Enter a word: ");
     text = in.next();in.nextLine();
     System.out.print("Enter a number to start the substring: ");
     positionToStart = in.nextInt();in.nextLine();
     System.out.print("Enter a number to end the substring: ");
     positionToEnd = in.nextInt();in.nextLine();
     theSubstring = text.substring(positionToStart,positionToEnd);
     System.out.println("Starting at position " + positionToStart + " and ending one letter BEFORE " + positionToEnd + " characters, results in: " + theSubstring);

    }

Code for method S_substring_Start_To_End_String():     
   
void S_substring_Start_To_End_String()//returns a part of a String starting from a given position to the end of the String
    {
     String text;
     String theSubstring;
     int positionToStart;
     System.out.print("Enter a word: ");
     text = in.next();in.nextLine();
     System.out.print("Enter a number to start the substring: ");
     positionToStart = in.nextInt();in.nextLine();

     theSubstring = text.substring(positionToStart);
     System.out.println("Starting at position " + positionToStart + " and going to the ending  results in: " + theSubstring);

    }