String Builder | Reverse a String (using StringBuilder class)| Get A Character from Index| Lecture 13 |

 Java - Introduction to Programming

Lecture 13

String Builder

Declaration

StringBuilder sb = new StringBuilder("Apna College");

     System.out.println(sb);

 

Get A Character from Index

StringBuilder sb = new StringBuilder("Tony");

     //Set Char

     System.out.println(sb.charAt(0));

 

Set a Character at Index

StringBuilder sb = new StringBuilder("Tony");

     //Get Char

     sb.setCharAt(0, 'P');

     System.out.println(sb);

 

Insert a Character at Some Index

import java.util.*;

 

public class Strings {

   public static void main(String args[]) {

     StringBuilder sb = new StringBuilder("tony");

     //Insert char

     sb.insert(0, 'S');

     System.out.println(sb);

   }

}

 

Delete char at some Index

import java.util.*;

 

public class Strings {

   public static void main(String args[]) {

     StringBuilder sb = new StringBuilder("tony");

     //Insert char

     sb.insert(0, 'S');

     System.out.println(sb);

 

//delete char

     sb.delete(0, 1);

     System.out.println(sb);

   }

}

Append a char 

Append means to add something at the end.

import java.util.*;

 

public class Strings {

   public static void main(String args[]) {

     StringBuilder sb = new StringBuilder("Tony");

     sb.append(" Stark");

     System.out.println(sb); 

   }

}

 

Print Length of String

import java.util.*;

 

public class Strings {

   public static void main(String args[]) {

     StringBuilder sb = new StringBuilder("Tony");

     sb.append(" Stark");

     System.out.println(sb); 

 

     System.out.println(sb.length());

   }

}

 

Reverse a String (using StringBuilder class)

import java.util.*;

 

public class Strings {

   public static void main(String args[]) {

     StringBuilder sb = new StringBuilder("HelloWorld");

    

     for(int i=0; i<sb.length()/2; i++) {

       int front = i;

       int back = sb.length() - i - 1;

 

       char frontChar = sb.charAt(front);

       char backChar = sb.charAt(back);

 

       sb.setCharAt(front, backChar);

       sb.setCharAt(back, frontChar);

     }

 

     System.out.println(sb);

   }

}

Homework Problems

Try Solving all the String questions with StringBuilder.