Java - String Buffer & String Builder Classes

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The StringBuffer and StringBuilder classes are used when there is a necessity to make a lot of modifications to Strings of characters.

Unlike Strings objects of type StringBuffer and Stringbuilder can be modified over and over again with out leaving behind a lot of new unused objects.

The StringBuilder class was introduced as of Java 5 and the main difference between the StringBuffer and StringBuilder is that StringBuilders methods are not thread safe(not Synchronised).

It is recommended to use StringBuilder whenever possible because it is faster than StringBuffer. However if thread safety is necessary the best option is StringBuffer objects.

Example:

public class Test{

    public static void main(String args[]){
       StringBuffer sBuffer = new StringBuffer(" test");
       sBuffer.append(" String Buffer");
       System.out.println(sBuffer);  
   }
}

This would produce the following result:

test String Buffer

StringBuffer Methods:

Here is the list of important methods supported by StringBuffer class:

SNMethods with Description
1public StringBuffer append(String s)
Updates the value of the object that invoked the method. The method takes boolean, char, int, long, Strings etc.
2public StringBuffer reverse()
The method reverses the value of the StringBuffer object that invoked the method.
3public delete(int start, int end)
Deletes the string starting from start index until end index.
4public insert(int offset, int i)
This method inserts an string s at the position mentioned by offset.
5replace(int start, int end, String str)
This method replaces the characters in a substring of this StringBuffer with characters in the specified String.

Here is the list of other methods (Except set methods ) which are very similar to String class:

SNMethods with Description
1int capacity()
Returns the current capacity of the String buffer.
2char charAt(int index)
The specified character of the sequence currently represented by the string buffer, as indicated by the index argument, is returned.
3void ensureCapacity(int minimumCapacity)
Ensures that the capacity of the buffer is at least equal to the specified minimum.
4void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
Characters are copied from this string buffer into the destination character array dst.
5int indexOf(String str)
Returns the index within this string of the first occurrence of the specified substring.
6int indexOf(String str, int fromIndex)
Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
7int lastIndexOf(String str)
Returns the index within this string of the rightmost occurrence of the specified substring.
8int lastIndexOf(String str, int fromIndex)
Returns the index within this string of the last occurrence of the specified substring.
9int length()
Returns the length (character count) of this string buffer.
10void setCharAt(int index, char ch)
The character at the specified index of this string buffer is set to ch.
11void setLength(int newLength)
Sets the length of this String buffer.
12CharSequence subSequence(int start, int end)
Returns a new character sequence that is a subsequence of this sequence.
13String substring(int start)
Returns a new String that contains a subsequence of characters currently contained in this StringBuffer.The substring begins at the specified index and extends to the end of the StringBuffer.
14String substring(int start, int end)
Returns a new String that contains a subsequence of characters currently contained in this StringBuffer.
15String toString()
Converts to a string representing the data in this string buffer.



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