StringBuffer class in Java

StringBuffer is a class in Java that represents a mutable sequence of characters. It provides an alternative to the immutable String class, allowing you to modify the contents of a string without creating a new object every time.

Features of StringBuffer Class

Here are some important features and methods of the StringBuffer class:

• StringBuffer objects are mutable, meaning that you can change the contents of the buffer without creating a new object.
• The initial capacity of a StringBuffer can be specified when it is created, or it can be set later with the ensureCapacity() method.
• The append() method is used to add characters, strings, or other objects to the end of the buffer.
• The insert() method is used to insert characters, strings, or other objects at a specified position in the buffer.
• The delete() method is used to remove characters from the buffer.
• The reverse() method is used to reverse the order of the characters in the buffer.

Here is an example of using StringBuffer to concatenate strings:

// Java Program to Demonstrate
// String Buffer

public class StringBufferExample {
    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);
    }
}

Hello world

Advantages of using StringBuffer in Java

There are several advantages of using StringBuffer over regular String objects in Java:

• Mutable: StringBuffer objects are mutable, which means that you can modify the contents of the object after it has been created. In contrast, String objects are immutable, which means that you cannot change the contents of a String once it has been created.
• Efficient: Because StringBuffer objects are mutable, they are more efficient than creating new String objects each time you need to modify a string. This is especially true if you need to modify a string multiple times, as each modification to a String object creates a new object and discards the old one.

Note: Both String and StringBuffer objects are thread safe.
StringBuffer is synchronized, making it thread-safe, but this does not mean that multiple threads can access it simultaneously without potential performance issues.
Immutable objects are by default thread-safe because their state can not be modified once created. Since String is immutable in Java, it’s inherently thread safe.

Overall, if you need to perform multiple modifications to a string, using StringBuffer can be more efficient than regular String objects.

StringBuffer is a peer class of String that provides much of the functionality of strings. The string represents fixed-length, immutable character sequences while StringBuffer represents growable and writable character sequences. StringBuffer may have characters and substrings inserted in the middle or appended to the end. It will automatically grow to make room for such additions and often has more characters preallocated than are actually needed, to allow room for growth.

StringBuffer class is used to create mutable (modifiable) strings. The StringBuffer class in Java is the same as the String class except it is mutable i.e. it can be changed.

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: 

import java.io.*;

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

Hello Java

2. insert() method

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

Example:

import java.io.*;

class A {
    public static void main(String args[])
    {
        StringBuffer sb = new StringBuffer("Hello ");
        sb.insert(1, "Java");
        // Now original string is changed
        System.out.println(sb);
    }
}

HJavaello 

3. replace() method

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

Example: 

import java.io.*;

class A {
    public static void main(String args[]) {
      
        StringBuffer sb = new StringBuffer("Hello");
        sb.replace(1, 3, "Java");
        System.out.println(sb);
    }
}

HJavalo

4. delete() method

The delete() method of the StringBuffer class deletes the string from the specified beginIndex to endIndex-1.

Example:

import java.io.*;

class A {
    public static void main(String args[]) {
      
        StringBuffer sb = new StringBuffer("Hello");
        sb.delete(1, 3);
        System.out.println(sb);
    }
}

Hlo

 5. reverse() method :

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

Example: 

import java.io.* ;

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

olleH

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 instance, if your current capacity is 16, it will be (16*2)+2=34.

Example: 

import java.io.*;

class A {
    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());
    }
}

16
16
34

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 class: 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 Program to Illustrate StringBuffer class
// via length() and capacity() methods

import java.io.*;

class GFG {
    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);
    }
}

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)

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

class GFG {
      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");

        // Returns GeeksforGeeks
        System.out.println(s);

        s.append(1);
        // Returns GeeksforGeeks1
        System.out.println(s);
    }
}

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.

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

class GFG {
    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");
        // Returns GeeksforGeeks
        System.out.println(s);

        s.insert(0, 5);
        // Returns 5GeeksforGeeks
        System.out.println(s);

        s.insert(3, true);
        // Returns 5GetrueeksforGeeks
        System.out.println(s);

        s.insert(5, 41.35d);
        // Returns 5Getr41.35ueeksforGeeks
        System.out.println(s);

        s.insert(8, 41.35f);
        // Returns 5Getr41.41.3535ueeksforGeeks
        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);
        // Returns 5Gpawanetr41.41.3535ueeksforGeeks
        System.out.println(s);
    }
}

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

class GFG {
    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();

        // Returns "skeeGrofskeeG"
        System.out.println(s);
    }
}

skeeGskeeG

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)

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

class GFG {
    public static void main(String[] args) {
      
        StringBuffer s = new StringBuffer("GeeksforGeeks");
        s.delete(0, 5);
   
        // Returns forGeeks
        System.out.println(s);

        s.deleteCharAt(7);
        
          // Returns forGeek
        System.out.println(s);
    }
}

forGeeks
forGeek

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)

Example

// Java Program to Illustrate StringBuffer class
// via replace() method

import java.io.*;

class GFG {
    public static void main(String[] args) {
      
        StringBuffer s = new StringBuffer("GeeksforGeeks");
        s.replace(5, 8, "are");

        // Returns GeeksareGeeks
        System.out.println(s);
    }
}

GeeksareGeeks

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Lokesh Todwal

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Article Tags :

• Java
• Java-lang package
• java-StringBuffer
• Java-Strings

Practice Tags :

• Java
• Java-Strings