Java - String Manipulation Concept

class str1
 {
   public static void main(String arg[])
     {
        String s1 = "Hello World";
        String s2 = "hello";
        String s3 = "world";
        String s4 = "JAVA";
        String s5 = "programming";
        String s6 = "hello";

        System.out.println("\nString : "+s1);

        System.out.println("\nLength : "+s1.length());

        System.out.println("\nConcatination : "+s2.concat(s3));

        System.out.println("\nSub String : "+s1.substring(6));

        System.out.println("\nSub String : "+s1.substring(3,8));

        System.out.println("\nEquals : "+s2.equals(s3));

        System.out.println("\nEquals : "+s2.equals(s6));

        System.out.println("\nUpper case : "+s5.toUpperCase());

        System.out.println("\nLower case : "+s4.toLowerCase());

        System.out.println("\nTrim : "+s1.trim());
    }
 }