Hi friend,

Strings are immutable (can't be changed), so manipulating strings often causes many temporary string objects to be created, which can be quite inefficient. StringBuilder (or StringBuffer) are better choices in these cases. Their toString() method can be used get a String value. It isn't necessary to create them with a specific size, it will expand as necessary. Many StringBuilder methods return the same StringBuilder so that the call chaining style of programming can be used. StringBuilder is basically identical to the older StringBuffer, but is slightly faster because it isn't synchronized.


StringBuilder

import javax.swing.*;

public class ReverseExample {
public static void main(String[] args) {
String input; // Used for the input string.
String reversed; // Reversed form or the input string.

while(true){
input = JOptionPane.showInputDialog(null, "Enter a string");
if(input == null)
break;
reversed = "";
for(int i=0; i<input.length(); i++) {
reversed = input.substring(i, i+1) + reversed;
}
JOptionPane.showMessageDialog(null, "Reversed:\n" + reversed);
}
}
}


StringBuffer classes

import java.io.*;

public class stringBufferExam{
public static void main(String[] args) throws Exception{
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
String str;
try{
System.out.print("Enter your name: ");
str = in.readLine();
System.out.println("This is the example of SringBuffer class and it's functions.");

//Create a object of StringBuffer class
StringBuffer buff = new StringBuffer();
buff.append(str);
System.out.println(buff);
buff.delete(0,str.length());

//append()
buff.append("Hello");
buff.append("World"); //print HelloWorld
System.out.println(buff);

//insert()
buff.insert(5,"_Java "); //print Hello_Java World
System.out.println(buff);

//reverse()
buff.reverse();
System.out.print("Reversed string : ");
System.out.println(buff); //print dlroW avaJ_olleH
buff.reverse();
System.out.println(buff); //print Hello_Java World

}
catch(StringIndexOutOfBoundsException e){
System.out.println(e.getMessage());
}
}
}
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read for more information,

http://www.roseindia.net/java/beginners/StringBuffer.shtml