String Buffer in Java

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

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

Important Constructors of StringBuffer class

Important methods of StringBuffer class

1)  StringBuffer append() method

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

class StringBufferExample{

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

}

}

2)  StringBuffer insert() method

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

class StringBufferExample2{

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

}

}

3)  StringBuffer replace() method

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

class StringBufferExample3{

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

}

}

4)  StringBuffer delete() and deleteCharAt() method

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

class StringBufferExample4{

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

}

}

5)  StringBuffer reverse() method

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

class StringBufferExample5{

public static void main(String args[]){ StringBuffer sb=new StringBuffer("Hello"); sb.reverse(); System.out.println(sb);//prints olleH

}

}

6)  charAt( ) and setCharAt( )

The value of a single character can be obtained from a StringBuffer via the charAt( ) method. You can set the value of a character within a StringBuffer using setCharAt( ).

7)  setLength( )

To set the length of the buffer within a StringBuffer object, use setLength( ). Its general form is shown here:

                           void setLength(int len)

Here, len specifies the length of the buffer. This value must be nonnegative.

8)  ensureCapacity( )

If you want to preallocate room for a certain number of characters after a StringBuffer has been constructed, you can use ensureCapacity( ) to set the size of the buffer. This is useful if you know in advance that you will be appending a large number of small strings to a StringBuffer.

ensureCapacity( ) has this general form:

                                      void ensureCapacity(int capacity)

Here, capacity specifies the size of the buffer.

9)  length( ) and capacity( )

The current length of a StringBuffer can be found via the length( ) method, while the total allocated capacity can be found through the capacity( ) method. They have the following general forms:

                                   int length( )

                                   int capacity( )

Output

buffer = Hello length = 5

capacity = 21

Since sb is initialized with the string “Hello” when it is created, its length is 5. Its capacity is 21 because room for 16 additional characters is automatically added.