11. Concat two Strings in java

class concat
{
public static void main(String a[])
{

    String s1="  hello  ";
    String s2="  world  ";

    System.out.println(s1);
    System.out.println(s2);

    String s3=s1.concat(s2);
    System.out.println(s3);


    String s4=s1.trim();
    System.out.println(s4);

    String s5=s2.trim();
    System.out.println(s5);

   

    String s6=s4.concat(s5);
    System.out.println(s6);
   
    System.out.println();
    String s7;
    s7=s6.replace('l','t');
    System.out.println(s7);
   
    String s7;
    s7=s6.replace('l','t');
    System.out.println(s7);


    System.out.println(s6.substring(3));
    System.out.println(s6.substring(3,6));

    System.out.println(s6.toLowerCase());

    System.out.println(s6.toUpperCase());

    System.out.println(s6.lastIndexOf('w'));
    System.out.println(s6.lastIndexOf("ll"));

}
}