capacity of a stringbuffer

[Naresh Gunda]

 
class Test
{
public static void main(String args[])
{
StringBuffer sb2=new StringBuffer(5);
System.out.println("Length : "+sb2.length());
System.out.println("Capacity : "+sb2.capacity());
 
sb2.append("abcdefgh");
System.out.println("Length : "+sb2.length());
System.out.println("Capacity : "+sb2.capacity());
 
sb2.append("ijklm");
System.out.println("Length : "+sb2.length());
System.out.println("Capacity : "+sb2.capacity());
}
}
 
Output:
 
Length : 0 //line1
Capacity : 5 //line2
Length : 8 //line3
Capacity : 12//line4
Length : 13//line5
Capacity : 26 //line6

Hi,
I didn't understand Line4 & Line6 in the output. Can any one explain me pls.

[Mylene Reiners]

Every string buffer has a capacity. As long as the length of the character sequence contained in the string buffer does not exceed the capacity, it is not necessary to allocate a new internal buffer array. If the internal buffer overflows, it is automatically made larger.

AFAIK there is no specific size give to enlarge it with, so it is decided by the VM... (when you google, you'll find figures like 16 bits, but it doesn't seem to be right).

[Chintamani Kashalikar]

When append method is called on a StringBuffer, first it checks for the available capacity (capacity() - length()) of the StringBuffer. If available capacity is less less than the length of string (or whatever you are appending). The capacity of the StringBuffer is increased. The new capacity is the larger of:

1. The length of string being appended.
2. Twice the old capacity, plus 2.

(Similar to ensureCapacity method of StringBuffer).


Cheers...........Chints

[Naresh Gunda]

Thanq Chints