import java.util.*;
public class StringExp {
public static void main(String args[])
{
    Scanner src=new Scanner(System.in);
    System.out.println("Enter String 1");
    String s1=src.next();
    System.out.println("Enter String 2");
    String s2=src.next();
    System.out.println("Concatenated String is : "+s1.concat(s2));
    System.out.println("String 1 in Upper Case: "+s1.toUpperCase());
    System.out.println("String 2 in Upper Case: "+s2.toUpperCase());
    System.out.println("Substring of String 1 :"+s1.substring(3,6));
    System.out.println(s2.toString());
    System.out.println("Enter one character");
    String s3=src.next();
    char z[]=s3.toCharArray();
    System.out.println("Replacement of String :"+s1.replace(z[0],'z'));
}
}

Output:- 

Enter String 1
Raamesh
Enter String 2
Liverpool
Concatenated String is : RaameshLiverpool
String 1 in Upper Case: RAAMESH
String 2 in Upper Case: LIVERPOOL
Substring of String 1 :mes
Liverpool
Enter one character
a
Replacement of String :Rzzmesh