Java StringBuffer: Usage and Examples

StringBuffer class is used to create a mutable string object i.e its state can be changed after it is created.The StringBuffer class are used when there is a necessity to make a lot of modifications to Strings of characters.

The StringBuilder classe are similar to the String class except that the String class is immutable.

The StringBuilder class is similar to StringBuffer except that the methods for modifying the buffer in StringBuffer are synchronized, which means that only one task is allowed to execute the methods.Use StringBuffer if the class might be accessed by multiple tasks con- currently.

StringBuffer Constructors

StringBuffer defines these four constructors:

StringBuffer( ) 
StringBuffer(int size) 
StringBuffer(String str) 
StringBuffer(CharSequence chars)

StringBuffer( )

The default constructor with no parameters.

Creates a StringBuffer object with an empty string placed in the buffer initially with a buffer capacity of 16 characters to store.

StringBuffer(int size)

It accepts an integer argument that explicitly sets the size of the buffer.

Creates a StringBuffer object with an empty string placed in the buffer initially with a buffer capacity of initialCapacity.

StringBuffer(String str)

It accepts a String argument that sets the initial contents of the StringBuffer object

Creates a StringBuffer object with string str placed in the buffer initially with a buffer capacity of 16 + str.length().

StringBuffer(CharSequence chars)

This constructor creates an object that contains the character sequence contained in chars.

Creates a StringBuffer object with CharSequence seq placed in the buffer initially with a buffer capacity of 16 + seq.length().

Program

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

  StringBuffer sb1 = new StringBuffer();
  StringBuffer sb2 = new StringBuffer(2);
  StringBuffer sb3 = new StringBuffer("Hello");
  StringBuffer sb4 = new StringBuffer('A');

  System.out.println("buffer = " + sb1);
  System.out.println("buffer = " + sb2);
  System.out.println("buffer = " + sb3);
  System.out.println("buffer = " + sb4);

  }
}
 

Output

 buffer =
buffer =
buffer = Hello
buffer =
Press any key to continue . . .
 

Two Important Method capacity() and length()

int length( )
int capacity( )

length()

Returns the number of characters present in the buffer(The current length of a StringBuffer) as an int value. By common sense also you can say, buffer length (number of characters present) cannot be more than the buffer capacity.

capacity()

Returns the buffer storing capacity as an int value. Initially the default constructor creates 16 buffer capacity and increases automatically when the buffer gets filled up with string. Programmer can place extra data in the buffer with append() method.

Let us illustrate the length and capacities through an example.

Program

// StringBuffer length vs. capacity.
class StringBufferDemo {

public static void main(String args[]) {

	StringBuffer strng = new StringBuffer("atnyla");

	System.out.println("buffer = " + strng);
	System.out.println("length = " + strng.length());
	System.out.println("capacity = " + strng.capacity());
 }
}

Output

buffer = atnyla
length = 6
capacity = 22
Press any key to continue . . .

Following example illustrates the usage of 4 types of StringBuffer Constructors.

Program

public class StringBufferDemoAll
{
  public static void main(String args[])
  {
   StringBuffer sb1 = new StringBuffer();
   System.out.println("sb1 length: " + sb1.length());
   // prints 0 as there is not data in the buffer
   System.out.println("sb1 capacity: " + sb1.capacity());
   // prints 16, the default capacity

   StringBuffer sb2 = new StringBuffer(50);
   System.out.println("sb2 length: " + sb2.length());
   // prints 0 as there is not data in the buffer
   System.out.println("sb2 capacity: " + sb2.capacity());
   // prints 50

   String str1 = "hello";
   StringBuffer sb3 = new StringBuffer(str1);
   System.out.println("sb3 length: " + sb3.length());
   // prints 5, the length of hello
   System.out.println("sb3 capacity: " + sb3.capacity());
   // prints 22; str1.length()+16

   CharSequence seq1 = "hello";
   StringBuffer sb4 = new StringBuffer(seq1);
   System.out.println("sb4 length: " + sb4.length());
   // prints 5, the length of hello
   System.out.println("sb4 capacity: " + sb4.capacity());
   // prints 22; str1.length()+16
 }
}

Output

sb1 length: 0
sb1 capacity: 16
sb2 length: 0
sb2 capacity: 50
sb3 length: 5
sb3 capacity: 21
sb4 length: 5
sb4 capacity: 21
Press any key to continue . . .

StringBuffer Methods