Thread: too many if's and else's!

My question is in regards to my code below. Basically, I've come to the point when I am using too many if's and else's and my program gets confused. The point of the first if is to check if the command line arguments anywhere contain just a's just b's or both simultaneiously. Assuming a and b stand for two different books, I want my program to print out whether I am starting one new book or two new books (respectively). I only want to make my first if work, I don't wish to change any other bits of the code unless absolutely nessesary.

public class TwoBookReader {
 
  public static void main(String args[])
 
  {
 
     PageCounter pca = new PageCounter();
     PageCounter pcb = new PageCounter();
 
     boolean changed = true;
     String book = "a"; 
     PageCounter currentBook = pca;
     int bookmark=0;
 
 
 
 
 
 
	 for(int i = 0; i < args.length; ++i)
     	 {	
 
		if (args[i].matches("[a]*") && args[i].matches("[b]*")) //CODE I WANT TO CHANGE...
			{
        		                         System.out.println("Starting two new books");
		    	}
 
 
         	if(args[i].equals("a"))
         	{
           	 book = "a";
	            currentBook = pca;
        	    changed = true;
        	 }
        	 else if(args[i].equals("b"))
	         {
        	    book = "b";
	            currentBook = pcb;
        	    changed = true;
	         }
		else if(args[i].equals("x"))
         	{
 
		bookmark=currentBook.whatPageAmIOn();
		System.out.println("Bookmarked page " + bookmark + " in " +book);
        	 }
 
		else if(args[i].equals("r"))
         	{
 
 
		System.out.println("Return to page " + bookmark + " in " +book);
        	 }
 
		 else
	         {
        	    if(!changed) 
			    {
	               		System.out.println("Still reading from "+book);
		            }
	            else
        	    	{
               		System.out.println("Reading from "+book);
            		}
 
 
		for(int j = 0;j < Integer.parseInt(args[i]);++j)
	            {
        	       System.out.println("Read page "+currentBook.whatPageAmIOn());
	               currentBook.readPage();
        	    }
	            System.out.println("Put "+book+" down");
        	    changed = false;
        	 }
    	}   
 
   }
}

This is what the program prints out. I don't know why it completely ignores the first if!

C:\Users\Downloads>java TwoBookReader
a 3 x 3 b 2 a r 2

Reading from a

Read page 1

Read page 2

Read page 3

Put a down

Bookmarked page 4 in a

Still reading from a

Read page 4

Read page 5

Read page 6

Put a down

Reading from b

Read page 1

Read page 2

Put b down

Return to page 4 in a

Reading from a

Read page 7

Read page 8

Put a down
----------------------
fanks!

You know what the point I was making is so either that's the only thing you read or you're really not here to help people but to waste your time writing useless sarcastic posts. Hope it was worth it

Lighten up. Don't take yourself so seriously.

Anybody who knows what causes the problem described in OP?

Thanks

the first if is to check if the command line arguments anywhere contain just a's just b's or both simultaneiously

The first if only checks one args[] element at a time each time through the for loop. Finding a or b anywhere in the array args[] can't happen with the statement as it's written. Can you see that? What you've described would require a nested for loop (or perhaps one in advance of the current for loop) to check every args[] element to see if both 'a' and 'b' were present.

Originally Posted by GregBrannon

The first if only checks one args[] element at a time each time through the for loop. Finding a or b anywhere in the array args[] can't happen with the statement as it's written. Can you see that? What you've described would require a nested for loop (or perhaps one in advance of the current for loop) to check every args[] element to see if both 'a' and 'b' were present.

Ok so I understand what you are trying to say but I still cannot see the problem myself so I tried this with a nested loop on top of the rest of the code anyway:

for(int k = 0; k < args.length; ++k)
     	 {
		 for(int m = 0; m < Integer.parseInt(args[k]); ++m)
     	 	 {
			if (args[k].matches("[a]*")  && args[k].matches("[b]*")) 
			{
        			System.out.println("Starting two new books");
		    	} 
		 }
	}

I'm getting a runtime error now, I think because it expects only integers but I'm not very sure:

javaTwoBookReader a 3 x 3 b 2 a r 2
Exception in thread "main" java.lang.NumberFormatException: For input string: "a"
at java.lang.NumberFormatException.forInputString(Unk nown Source)
at java.lang.Integer.parseInt(Unknown Source)
at java.lang.Integer.parseInt(Unknown Source)
at TwoBookReader.main(TwoBookReader.java:15)

Oh, and you missed the solution posted by Sambit. Too bad.

As you've correctly pointed out, this statement:

if ( args[i].matches("[a]*") && args[i].matches("[b]*") )

is the problem. Since 'i' will always be the same in the above comparison the result will always be false. The index must vary from 'i' to compare the first to THE REST of the elements in the args[] array, something like:

if ( args[i].matches("[a]*") && args[j].matches("[b]*") )

where j varies from i to args.length. That second index variable, j, would typically be controlled by a nested loop.

OR if you know that the second book, b, will always be a specific element number and 'a' is always at index 0, you could simply compare the contents of those 2 indices:

if ( args[0].matches("[a]*") && args[4].matches("[b]*") )

but I don't know if that's always the case.

Good luck!