String Buffer (Part 1)

Pre-requisites:- Strings 

String Buffer

In Java , Strings are immutable i.e once declared cannot be changed. The StringBuffer class can create mutable strings. The only difference between String class and StringBuffer class is that StringBuffer creates mutable strings.

Important StringBuffer Methods:-

1. StringBuffer length( ) method

The length( ) method returns the length of the string.

 public class MyClass {  
      public static void main(String[] args) {  
   
           // create a StringBuffer object 'sb'  
           StringBuffer sb = new StringBuffer("Hello");  
           System.out.println(sb.toString()); // outputs Hello   
   
           System.out.println(sb.length()); // outputs 5  
   
      }  
 }  

The .toString( ) displays StringBuffer in the form of a string.

2. StringBuffer append( string ) method

The append( ) method concatenates the string entered as argument in it.

 public class MyClass {  
      public static void main(String[] args) {  
          
           //create a StringBuffer object 'sb'  
           StringBuffer sb=new StringBuffer("Hello");  
           System.out.println(sb.toString()); //outputs Hello 
            
           sb.append(" Java Monk"); //adds string to sb  
           sb.append("!"); //adds string to sb  
           System.out.println(sb.toString()); //outputs Hello Java Monk !  
      }  
 }  

3. StringBuffer insert( int beginIndex, string  ) method

The insert( ) method inserts specified string at user defined index.

 public class MyClass {  
      public static void main(String[] args) {  
             
           //create a StringBuffer object 'sb'  
           StringBuffer sb=new StringBuffer("Hello");  
           System.out.println(sb.toString()); //outputs Hello  
             
           sb.insert(2,"!!!"); //inserts '!!!' at index 2  
           System.out.println(sb.toString());  //outputs He!!!llo  
      }  
 }  

4. StringBuffer replace( int beginIndex, int endIndex, string ) method

The replace( ) method replaces the given string from the specified beginIndex and endIndex.

 public class MyClass {  
      public static void main(String[] args) {  
             
           //create a StringBuffer object 'sb'  
           StringBuffer sb=new StringBuffer("Hello");  
           System.out.println(sb.toString()); //outputs Hello  
             
           sb.replace(1, 2, "Java Monk"); //inserts 'Java Monk' at between Hello at specified index   
           System.out.println(sb.toString());  //outputs HJava Monkllo  
      }  
 }  

5. StringBuffer delete( int beginIndex, int endIndex ) method

The delete( ) method deletes the string character between specified beginning and ending indexes.

 public class MyClass {  
      public static void main(String[] args) {  
             
           //create a StringBuffer object 'sb'  
           StringBuffer sb=new StringBuffer("HelloWorld");  
           System.out.println(sb.toString()); //outputs HelloWorld  
             
           sb.delete(3 , 7); //deletes characters between indexes 3 to 7  
           System.out.println(sb.toString());  //outputs Helrld  
      }  
 }  

6. StringBuffer substring( int beginIndex, int endIndex ) method

The substring( ) method returns the string from specified index.

 public class MyClass {  
      public static void main(String[] args) {  
   
           // create a StringBuffer object 'sb'  
           StringBuffer sb = new StringBuffer("Hello Java Monk");  
           System.out.println(sb.toString()); // outputs Hello Java Monk  
   
           System.out.println(sb.substring(2, 10)); // outputs llo Java  
   
      }  
 }  

7. StringBuffer charAt( index i ) method

The charAt( ) returns the character at specified index.

 public class MyClass {  
      public static void main(String[] args) {  
   
           // create a StringBuffer object 'sb'  
           StringBuffer sb = new StringBuffer("Hello Java Monk");  
           System.out.println(sb.toString()); // outputs Hello Java Monk  
   
           System.out.println(sb.charAt(6)); // outputs J  
   
      }  
 }  

8. StringBuffer indexOf( string ) method

The indexOf( ) method returns the index of specified string character. If string not found , returns -1.

 public class MyClass {  
      public static void main(String[] args) {  
   
           // create a StringBuffer object 'sb'  
           StringBuffer sb = new StringBuffer("Hello Java Monk");  
           System.out.println(sb.toString()); // outputs Hello Java Monk  
   
           System.out.println(sb.indexOf("M")); // outputs 11  
             
           System.out.println(sb.indexOf("s")); //outputs -1  
      }  
 }  

9. StringBuffer reverse( ) method

The reverse( ) method reverse characters position of entered string.

 public Myclass {  
      public static void main(String[] args) {  
             
           //create a StringBuffer object 'sb'  
           StringBuffer sb=new StringBuffer("Hello");  
           System.out.println(sb.toString()); //outputs Hello  
             
           sb.reverse(); //reverse string  
           System.out.println(sb.toString());  //outputs olleH  
      }  
 }  

10. StringBuffer capacity( ) method

The capacity( ) method , is used to return the current capacity.

 public class MyClass {  
      public static void main(String[] args) {  
   
           // create a StringBuffer object 'sb'  
           StringBuffer sb = new StringBuffer("");  
           System.out.println(sb.toString()); // outputs blank line  
   
           System.out.println(sb.capacity()); // outputs default capacity i.e 16  
   
           StringBuffer sb1 = new StringBuffer("Hello there, It is Java Monk");  
           System.out.println(sb1.capacity()); // outputs capacity 44  
   
      }  
 }  

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