Triangle in Java

String s = "abcdefghijklmnopqrstuvwxyz"

int len = s.length();

for(int i = 0; i < len; i++){
    System.out.println( s.subString( 0, len - i) );
}

I don't understand the above statement, I am still a beginner in Java. Below is my programme but it does not work, can you kindly advise.  Thanks.

class Lab_02c {
      public static void main (String[] args) {      //keyboard input:an int
            int x = Integer.parseInt(args[0]);

            if (x <= 26 && x > 0) {      
                  for (int i = 26-x; i < 26; ++i) {
                      for (int j = i; j < i; ++j) {
                              System.out.print(" ");
                }
                char ch ='a';
                    for (int j = 1; j < 26; ++j) {
                              ch = ++ch;
                                    System.out.print(ch);
                              }    
                            System.out.println();
                  }
            }
            else {
            System.out.println("Size out of range!");
            }
      }
}

this looks like homework...

thanks for all the comments but its too difficult for me to understand. i have stick with my original programme n found the mistakes.

I'm quite happy to explain it! It's better to start with something that works than doesn't work ;-)

Your code when modifed as the following works

public static void main (String[] args) {    
  int x = Integer.parseInt(args[0]);

             if (x <= 26 && x > 0)
             {
                for (int i = 26-x; i < 26; ++i)
                {
                   for (int j = 26-i; j < 26; ++j)
                   {
                            System.out.print(" ");
                   }
                   char ch ='a';
                   for (int j = 0; j < 26-i; ++j)
                   {
                     System.out.print(ch);
                     ch = ++ch;
                   }
                   System.out.println();
                }
             }
             else
             {
             System.out.println("Size out of range!");
             }
}

>>  ch = ++ch;

this is a very confusing line.
you should simply replace it by

>>  ch++;
or
>>  ++ch;
or
>>  ch += 1;
or
>>  ch = ch + 1;

compile this in ur compiler and run as "java Lab_02c 26". u will get what u want with ur same code with errors corrected.
class Lab_02c  {
    public static void main (String[] args) {     //keyboard input:an int
         int x = Integer.parseInt(args[0]);

         if (x <= 26 && x > 0) {    
               for (int i = 26-x; i < 26; ++i) {
                  for (int j = 0; j < i; ++j) // earlier this condition will not print space at all, coz if j=1 it can never be less than i
                  { // now this is changed to start from a to whatever is the current loop count.
                        System.out.print(" ");
                   }

             char ch ='a';
                 for (int j = i; j < x; ++j) {// it was earlier printing a to z always, but it shud not. it shud only print increment values
                       
                             System.out.print(ch);
                             ch = ++ch; // this line was above print statement. so earlier it will start printing only from 'b'
                        }    
                       System.out.println();
              }
         }
         else {
         System.out.println("Size out of range!");
         }
    }
}

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