13 Jul StringBuffer class in Java

StringBuffer in Java is used to create modifiable strings i.e. it doesn’t have a fixed length like the String class in Java. The StringBuffer class has growable and writable character sequences.  It is thread safe i.e. multiple threads cannot simultaneously access the same method.

Let us see how to create a string using StringBuffer:

StringBuffer strBuff = new StringBuffer("dwa");

StringBuffer class Constructors

The constructors of StringBuffer are displayed below:

StringBuffer class Methods

The methods of StringBuffer are displayed below with a description:

For complete reference of the StringBuffer methods, refer to the Oracle Java StringBuffer docs.

StringBuffer Examples

The following are some of the examples of StringBuffer:

Append the string representation in StringBuffer

The append() method in Java appends the string representation. Here, append(char ch) appends the string representation of the char argument to this sequence.

// Append the string representation with StringBuffer

class Demo66 {
    static void main(String[] args) {

        StringBuffer message = new StringBuffer("ABCD");
        System.out.println(message);

        // append
        message.append('E');

        System.out.println("The updated string = "+message);
    }
}

Output

ABCD
The updated string = ABCDE

Find the current capacity of a string in a StringBuffer

To fetch the current capacity, the capacity() method is used in Java:

import java.lang.*;

public class StudyopediaDemo {

   public static void main(String[] args) {

      StringBuffer strBuff = new StringBuffer("Dwa");
      System.out.println("StringBuffer = " + strBuff);
      
      // capacity will be 16 + 3
      System.out.println("capacity = " + strBuff.capacity());
    
      // append
      strBuff.append('y');
      
      System.out.println("Updated = " + strBuff);
     }
}

The output is as follows:

StringBuffer = Dwa
capacity = 19
Updated = Dway

Reverse the value of the StringBuffer object

To reverse the value of the StringBuffer object, the reverse() method in Java is to be used. Let us see an example:

import java.lang.*;

public class StudyopediaDemo {

   public static void main(String[] args) {

      StringBuffer strBuff = new StringBuffer("Dwa");
      System.out.println("StringBuffer = " + strBuff);
      
      // capacity will be 16 + 3
      System.out.println("capacity = " + strBuff.capacity());
    
      // append
      strBuff.append('y');
      
      System.out.println("Updated = " + strBuff);
      
      // append
      strBuff.append('n');
      
      System.out.println("Updated = " + strBuff);
      
      // append
      strBuff.append('e');
      
      System.out.println("Final StringBuffer = " + strBuff);
      
      System.out.println("Final StringBuffer (Reverse)= " + strBuff.reverse());
   }
}

The output is as follows:

StringBuffer = Dwa
capacity = 19
Updated = Dway
Updated = Dwayn
Final StringBuffer = Dwayne
Final StringBuffer (Reverse)= enyawD

StringBuffer vs. String

The String class has a fixed length i.e. cannot be changed, whereas StringBuffer is growable and creates modifiable (mutable) strings. Let us now see the differences:

Let us now see an example to understand the difference between String and StringBuffer object:
The append() method in Java appends the string representation. Here, we will also understand the difference between a String and a StringBuffer object.

// Append the String representation (StringBuffer)
// Understand the difference between String and StringBuffer object

class Demo69 {
    static void main(String[] args) {

        String s = "ABCDE";
        s = s + "FGHIJ"; // create a new string object
        System.out.println(s);

        StringBuffer sb = new StringBuffer("ABCDE");
        sb.append("FGHIJ"); // modifies the same object
        System.out.println(sb);
    }
}

Output

ABCDEFGHIJ
ABCDEFGHIJ