StringBuffer Class in Java (original) (raw)

Last Updated : 18 Apr, 2025

The **StringBuffer class in Java represents a sequence of characters that can be modified, which means we can change the content of the StringBuffer without creating a new object every time. It represents a mutable sequence of characters.

Features of StringBuffer Class

The key features of StringBuffer class are listed below:

• Unlike String, we can modify the content of the StringBuffer without creating a new object.
• StringBuffer has an initial capacity, and it can also be adjusted later with the help of the ensureCapacity() method.
• With the help ofthe append() method, we can add characters, strings, or objects at the end of the StringBuffer.
• With the help ofthe insert() method, we can insert characters, strings, or objects at a specified position in the StringBuffer.
• With the help of the **delete() method, we can remove characters from the StringBuffer.
• With the help of **reverse() method, we can reverse the order of characters in the StringBuffer.

**Example: Here is an example of using StringBuffer to concatenate strings:

Java `

//Demonstrating String Buffer public class Geeks { public static void main(String[] args){

      // Creating StringBuffer
    StringBuffer s = new StringBuffer();
  
      // Adding elements in StringBuffer
    s.append("Hello");
    s.append(" ");
    s.append("world");
    
      // String with the StringBuffer value
      String str = s.toString();
    System.out.println(str);
}

}

`

Advantages of using StringBuffer in Java

The advanatages of StringBuffer class are listed below:

• **Mutable: StringBuffer are mutable it means that we can change the content after the object has been created, on the other hand String are immutable once it created it can not be modified.
• **Efficient: Since StringBuffer objects are mutable, it is suitable in scenarios where we need to modify the string multiple times. If we do the same thing with string, everytime a new object is created and the old one is deleted, which is very bad in terms of performance and memory.

**Note: Both String and StringBuffer objects are thread safe, but in different ways. StringBuffer is synchronized it means it is thread-safe but keep in mind that this synchronization can cause performance issues if accessed by multiple threads at the same time. On the other hand immutable objects like String are thread-safe because their state can not be modified once they are created.

Constructors of StringBuffer Class

Methods of Java StringBuffer Class

Examples of Java StringBuffer Method

1. append() Method

The **append() method concatenates the given argument with this string.

**Example:

Java `

import java.io.*;

class Geeks { public static void main(String args[]) { StringBuffer sb = new StringBuffer("Hello "); sb.append("Java"); // now original string is changed System.out.println(sb); } }

`

2. insert() Method

The **insert() method inserts the given string with this string at the given position.

**Example:

Java `

import java.io.*;

class Geeks { public static void main(String args[]) { StringBuffer sb = new StringBuffer("Hello "); sb.insert(1, "Java");

    // Now original string is changed
    System.out.println(sb);
}

}

`

3. replace() Method

The **replace() method replaces the given string from the specified beginIndex and endIndex-1.

**Example:

Java `

import java.io.*;

class Geeks { public static void main(String args[]) {

    StringBuffer sb = new StringBuffer("Hello");
    sb.replace(1, 3, "Java");
    System.out.println(sb);
}

}

`

4. delete() Method

The **delete() method is used to delete the string from the specified beginIndex to endIndex-1.

**Example:

Java `

import java.io.*;

class Geeks { public static void main(String args[]) {

    StringBuffer sb = new StringBuffer("Hello");
    sb.delete(1, 3);
    System.out.println(sb);
}

}

`

5. reverse() Method

The **reverse() method of the StringBuffer class reverses the current string.

**Example:

Java `

import java.io.* ;

class Geeks { public static void main(String args[]) { StringBuffer sb = new StringBuffer("Hello"); sb.reverse(); System.out.println(sb); } }

`

6. capacity() Method

• The **capacity() method of the StringBuffer class returns the current capacity of the buffer. The default capacity of the buffer is 16. If the number of characters increases from its current capacity, it increases the capacity by (oldcapacity*2)+2.
• For example, if the current capacity is 16, it will be (16*2)+2=34.

**Example:

Java `

import java.io.*;

class Geeks { public static void main(String args[]) { StringBuffer sb = new StringBuffer();

      // default 16
    System.out.println(sb.capacity()); 
    sb.append("Hello");
  
      // now 16
    System.out.println(sb.capacity()); 
    sb.append("java is my favourite language");
    
      // (oldcapacity*2)+2
      System.out.println(sb.capacity());
}

}

`

Some Interesting Facts about the StringBuffer Class

Do keep the following points in the back of your mind:

• **java.lang.StringBuffer extends (or inherits from) Object class.
• All Implemented Interfaces of StringBuffer classes are **Serializable, Appendable, CharSequence.
• **public final class StringBuffer extends **Object implements **Serializable, CharSequence, Appendable.
• **String buffers are safe for use by multiple threads. The methods can be synchronized wherever necessary so that all the operations on any particular instance behave as if they occur in some serial order.
• Whenever an operation occurs involving a source sequence (such as appending or inserting from a source sequence) this class synchronizes only on the string buffer performing the operation, not on the source.
• It inherits some of the methods from the Object class which such as **clone(), equals(), finalize(), getClass(), hashCode(), notifies(), notifyAll().

**Remember: StringBuilder, J2SE 5 adds a new string class to Java’s already powerful string handling capabilities. This new class is called StringBuilder. It is identical to StringBuffer except for one important difference: it is not synchronized, which means that it is not thread-safe.

The advantage of StringBuilder is faster performance. However, in cases in which you are using multithreading, you must use StringBuffer as it is thread-safe rather than StringBuilder.

Other Methods in Java StringBuffer

These auxiliary methods are as follows:

**Note: Above we only have discussed the most widely used methods and do keep a tight bound around them as they are widely used in programming geeks.

Examples of the above Methods

Example 1: length() and capacity() Methods

Java `

// Java Program to Illustrate StringBuffer class // via length() and capacity() methods import java.io.*;

class Geeks { public static void main(String[] args) {

    // Creating and storing string by creating object of
    // StringBuffer
    StringBuffer s = new StringBuffer("GeeksforGeeks");

    // Getting the length of the string
    int p = s.length();

    // Getting the capacity of the string
    int q = s.capacity();

    // Printing the length and capacity of
    // above generated input string on console
    System.out.println("Length of string GeeksforGeeks="
                       + p);
    System.out.println("Capacity of string GeeksforGeeks="
                       + q);
}

}

`

Output

Length of string GeeksforGeeks=13 Capacity of string GeeksforGeeks=29

Example 2: append()

It is used to add text at the end of the existing text. Here are a few of its forms:

StringBuffer append(String str)
StringBuffer append(int num)

**Illustration:

Java `

// Java Program to Illustrate StringBuffer class // via append() method import java.io.*;

class Geeks { public static void main(String[] args){

    // Creating an object of StringBuffer class and
    // passing random string
    StringBuffer s = new StringBuffer("Geeksfor");

    // Usage of append() method
    s.append("Geeks");

    System.out.println(s);

    s.append(1);
    
    System.out.println(s);
}

}

`

Output

GeeksforGeeks GeeksforGeeks1

Example 3: insert()

It is used to insert text at the specified index position. Syntax of method is mentioned below:

StringBuffer insert(int index, String str)
StringBuffer insert(int index, char ch)

Here, the index specifies the index at which point the string will be inserted into the invoking StringBuffer object.

**Illustration:

Java `

// Java Program to Illustrate StringBuffer class // via insert() method import java.io.*;

class Geeks { public static void main(String[] args) {

    // Creating an object of StringBuffer class
    StringBuffer s = new StringBuffer("GeeksGeeks");

    // Inserting element and position as an arguments
    s.insert(5, "for");

    System.out.println(s);

    s.insert(0, 5);

    System.out.println(s);

    s.insert(3, true);

    System.out.println(s);

    s.insert(5, 41.35d);

    System.out.println(s);

    s.insert(8, 41.35f);

    System.out.println(s);

    // Declaring and initializing character array
    char geeks_arr[] = { 'p', 'a', 'w', 'a', 'n' };

    // Inserting character array at offset 9
    s.insert(2, geeks_arr);

    System.out.println(s);
}

}

`

Output

GeeksforGeeks 5GeeksforGeeks 5GetrueeksforGeeks 5Getr41.35ueeksforGeeks 5Getr41.41.3535ueeksforGeeks 5Gpawanetr41.41.3535ueeksforGeeks

Example 4: reverse( )

It can reverse the characters within a StringBuffer object using **reverse( ). This method returns the reversed object on which it was called.

Java `

// Java Program to Illustrate StringBuffer class // via reverse() method import java.io.*;

class Geeks { public static void main(String[] args){

    // Creating a string via creating
    // object of StringBuffer class
    StringBuffer s = new StringBuffer("GeeksGeeks");

    // Invoking reverse() method
    s.reverse();

    System.out.println(s);
}

}

`

Example 5: delete( ) and deleteCharAt()

It can delete characters within a StringBuffer by using the methods **delete( ) and **deleteCharAt( ). The **delete( ) method deletes a sequence of characters from the invoking object. Here, the start Index specifies the index of the first character to remove, and the end Index specifies an index one past the last character to remove. Thus, the substring deleted runs from start Index to endIndex–1. The resulting StringBuffer object is returned. The deleteCharAt( ) method deletes the character at the index specified by loc. It returns the resulting StringBuffer object.

**Syntax:

StringBuffer delete(int startIndex, int endIndex)
StringBuffer deleteCharAt(int loc)

**Illustration:

Java `

// Java Program to Illustrate StringBuffer class // via delete() and deleteCharAt() Methods import java.io.*;

class Geeks { public static void main(String[] args) {

    StringBuffer s = new StringBuffer("GeeksforGeeks");
    s.delete(0, 5);

    System.out.println(s);

    s.deleteCharAt(7);

    System.out.println(s);
}

}

`

Example 6: replace()

It can replace one set of characters with another set inside a StringBuffer object by calling **replace( ). The substring being replaced is specified by the indexes start Index and endIndex. Thus, the substring at start Index through endIndex–1 is replaced. The replacement string is passed in str. The resulting StringBuffer object is returned.

**Syntax:

StringBuffer replace(int startIndex, int endIndex, String str)

**Illustration:

Java `

// Java Program to Illustrate StringBuffer class // via replace() method import java.io.*;

class Geeks { public static void main(String[] args) {

    StringBuffer s = new StringBuffer("GeeksforGeeks");
    s.replace(5, 8, "are");

    System.out.println(s);
}

}

`