Java StringBuffer class

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StringBuffer is a peer class of String that provides much of the functionality of strings. 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.

Important Constructors of StringBuffer class
ConstructorDescription
StringBuffer() creates an empty string buffer with the initial capacity of 16.
StringBuffer(String str) creates a string buffer with the specified string.
StringBuffer(int capacity) creates an empty string buffer with the specified capacity as length.
Important methods of StringBuffer class
Modifier and TypeMethodDescription
public synchronized StringBufferappend(String s) is used to append the specified string with this string. The append() method is overloaded like append(char), append(boolean), append(int), append(float), append(double) etc.
public synchronized StringBuffer insert(int offset, String s) is used to insert the specified string with this string at the specified position. The insert() method is overloaded like insert(int, char), insert(int, boolean), insert(int, int), insert(int, float), insert(int, double) etc.
public synchronized StringBuffer replace(int startIndex, int endIndex, String str) is used to replace the string from specified startIndex and endIndex.
public synchronized StringBuffer delete(int startIndex, int endIndex) is used to delete the string from specified startIndex and endIndex.
public synchronized StringBuffer reverse() is used to reverse the string.
public int capacity() is used to return the current capacity.
public void ensureCapacity(int minimumCapacity) is used to ensure the capacity at least equal to the given minimum.
public char charAt(int index) is used to return the character at the specified position.
public int length() is used to return the length of the string i.e. total number of characters.
public String substring(int beginIndex) is used to return the substring from the specified beginIndex.
public String substring(int beginIndex, int endIndex) is used to return the substring from the specified beginIndex and endIndex.
What is mutable string

A string that can be modified or changed is known as mutable string. StringBuffer and StringBuilder classes are used for creating mutable string.

1) StringBuffer append() method

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


import java.io.*;
class StringBuffer
{  
public static void main(String args[])
{  
StringBuffer sb=new StringBuffer("Hello ");  
sb.append("Java"); 
System.out.println(sb);//prints Hello Java  
}  
}


Output:


Hello Java
2) StringBuffer insert() method

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


import java.io.*;
class StringBuffer
{  
public static void main(String args[])
{  
StringBuffer sb=new StringBuffer("Hello ");  
sb.insert(1,"Rama"); 
System.out.println(sb);  
}  
}


Output:


HRamaello
3) StringBuffer replace() method

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


import java.io.*;
public class Test
{  
public static void main(String args[])
{  
StringBuffer sb=new StringBuffer("Hello");  
sb.replace(1,2,"Rama");  
System.out.println(sb);
}  
}


Output:

Hjavallo
4) StringBuffer delete() method

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


import java.io.*;
public class Test
{  
public static void main(String args[]){  
StringBuffer sb=new StringBuffer("India");  
sb.delete(1,3);  
System.out.println(sb);
}  
}


Output:


Iio
5) StringBuffer reverse() method

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


import java.io.*;
public class Test
{  
public static void main(String args[])
{  
StringBuffer sb=new StringBuffer("School");  
sb.reverse();  
System.out.println(sb);
}  
}


Output:

loohcS
6) StringBuffer capacity() method

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


import java.io.*;
class StringBuffer
{  
public static void main(String args[])
{  
StringBuffer sb=new StringBuffer();  
System.out.println(sb.capacity());//default 16  
sb.append("Hello");  
System.out.println(sb.capacity());//now 16  
sb.append("java is my favourite language");  
System.out.println(sb.capacity());//now (16*2)+2=34 i.e (oldcapacity*2)+2  
}  
}


Output:



16
16
34
7) StringBuffer ensureCapacity() method

The ensureCapacity() method of StringBuffer class ensures that the given capacity is the minimum to the current capacity. If it is greater than the current capacity, it increases the capacity by (oldcapacity*2)+2. For example if your current capacity is 16, it will be (16*2)+2=34.


import java.io.*;
class StringBuffer
{  
public static void main(String args[]){  
StringBuffer sb=new StringBuffer();  
System.out.println(sb.capacity());//default 16  
sb.append("Hello");  
System.out.println(sb.capacity());//now 16  
sb.append("java is my favourite language");  
System.out.println(sb.capacity());//now (16*2)+2=34 i.e (oldcapacity*2)+2  
sb.ensureCapacity(10);//now no change  
System.out.println(sb.capacity());//now 34  
sb.ensureCapacity(50);//now (34*2)+2  
System.out.println(sb.capacity());//now 70  
}  
}


Output:


16
16
34
34
70
Some Interesting facts:

  1. java.lang.StringBuffer extends (or inherits from) Object class.

  2. All Implemented Interfaces of StringBuffer class:Serializable, Appendable, CharSequence.

  3. public final class StringBuffer extends Object implements Serializable, CharSequence

  4. 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.

  5. 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.

  6. It inherits some of the methods from Object class which are clone, equals, finalize, getClass, hashCode, notify, notifyAll.

    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 rather than StringBuilder.




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