questions on this code

[Alex Derek]

Hello everybody,

i wanted to ask, to the holy and patients ones, to take a look at this code and help me, if possible, with some questions.

This is a program i'm creating to help me learn and remember various method of String and String Builder.
The program asks the user to insert a String, then asks to answer correctly on the result of a given String method
(indexOf in code reported) applied to the string inserted. If the answer is not type-correct (in indexOf has to be a number)
the program asks the same question again.
The value of the parameters are created dinamically based on the string inserted by the user.
The code works fine.
My questions are about the better way (if there is a better way) to implement this code.
After editing three times (cursed the back button of the browser grrrrrr...), i've tried to lighten the most the topic.
Hope it's a bit better.
Ok, here is the code:

	/* this method takes the input (a String) inserted from the user,
	creates a random number based on the length of the string inserted,
	use this random number as parameter for indexOf(int ch) on the input
	given from the user and  questions the user on the result.
	 */
	public void indexOfParamInt() 
	{
		int idOfMethod = 1;
		// i added to every method an id, which is passed as a 
                    parameter to the checkAnswerInput() method. 
		resultOfMethod = 
                firstInput.indexOf(firstInput.charAt(generateRandomNumber(firstInput.length())));
		answerInput = user.getUserInput("What is the result of method \"indexOf(int ch)\" 
\n indexOf(" + firstInput.charAt(resultOfMethod) 
+") applied on your string?");
		// if checkAnswerInput return is not true checkResult don't run.
		if(!checkAnswerInput(answerInput, idOfMethod))
		{
			return;
		}
		checkResult();
	}
	/* this method takes the input (a String) inserted from the user,
	creates a random number based on the length of the string inserted
	and apply the method answerInput on another random number,use these
	random numbers as parameters for indexOf(int ch, int fromIndex) on
	the string inserted from the user and questions the user on the
	result.*/
	public void indexOfParamIntInt()
	{
		int idOfMethod = 2; 
		char ch = firstInput.charAt(generateRandomNumber(firstInput.length()));
		int ran = generateRandomNumber(firstInput.length());
		resultOfMethod = firstInput.indexOf(ch, ran);
		answerInput = user.getUserInput("What is the result of method \"
indexOf(int ch, int fromIndex)\" \n indexOf(" + ch + ", " + ran +")
 applied on your string?");
		if(!checkAnswerInput(answerInput, idOfMethod))
		{
			return;
		}
		checkResult();
	}
	/* this method takes the input (a String) inserted from the user,
	creates a substring based on the string inserted(using two random
	number, the second is created through method
	secondNumberForSubString because it has to be bigger than the
	first), and apply the method indexOf(String str) on the string of
	the user and questions him on the result.*/	
	public void indexOfParamStr()
	{
		int idOfMethod = 3;
		int ran = generateRandomNumber(firstInput.length());
		int ran1 = secondNumberForSubString(ran);
		String subStringOfUserInput = firstInput.substring(ran, ran1);
		resultOfMethod = firstInput.indexOf(subStringOfUserInput);
		answerInput = user.getUserInput("What is the result of method 
\"indexOf(String str)\" \n indexOf(" + subStringOfUserInput 
+") applied on your string?");
		if(!checkAnswerInput(answerInput, idOfMethod))
		{
			return;
		}
		checkResult();		
	}
	/* this method takes the input (a String) inserted from the user,
	creates a substring based on the string inserted, apply
	indexOf(String str, int fromIndex) on the string and 
	questions the user on the result.*/
	public void indexOfParamStrInt()
	{
		int idOfMethod = 4;
		int ran = generateRandomNumber(firstInput.length());
		int ran1 = secondNumberForSubString(ran);
		int ran2 = generateRandomNumber(firstInput.length());
		String subStringOfUserInput = firstInput.substring(ran, ran1);
		resultOfMethod = firstInput.indexOf(subStringOfUserInput, ran2);
		answerInput = user.getUserInput("What is the result of method
\"indexOf(String str, int fromIndex)\" \n indexOf(" 
+ subStringOfUserInput + ", " + ran2 +") applied on your string?");
		if(!checkAnswerInput(answerInput, idOfMethod))
		{
			return;
		}
		checkResult();		
	}
	/* This method takes the answer inserted by the user and check if
	it's a correct value (in this case an int value).*/
	public boolean checkAnswerInput(String answerI, int idOfMethod)
	{
		boolean check = true;
		for(int i = 0; i < answerI.length(); i++)
		{
			if(!((answerI.charAt(i) >= '0') && (answerI.charAt(i) <= '9')))
			{
				check = false; 
				System.out.println("Sorry, but this method requests an 
              integer as answer, so you have \nto insert a number. Try again!");
				// creating a switch construct to redirect the user on 
                                // the question which he gave the wrong type answer.
				switch(idOfMethod)
				{
				case 1: indexOfParamInt();
					break;
				case 2: indexOfParamIntInt();
					break;
				case 3: indexOfParamStr();
					break;
				case 4: indexOfParamStrInt();
					break;
				}
			/*	ok, this one is the implementation using an if else if
			construct instead of a switch.
			* if(idOfMethod == 1)
			*	{
			*		indexOfParamInt();
			*	}
			*	else if(idOfMethod == 2)
			*	{
			*		indexOfParamIntInt();
			*	}
			*	else if(idOfMethod == 3)
			*	{
			*		indexOfParamStr();
			*	}
			*	else
			*	{
			*		indexOfParamStrInt();
			*	}
			*/
			}
		}
		return check;
	}
				
		
//this method takes the answer of the user and compare it with the
//result of the method.	
	public void checkResult()
	{
		answerOfUser = Integer.parseInt(answerInput);
		if (resultOfMethod == answerOfUser)
		{
			System.out.println("correct!");
		}
		else
		{
			System.out.println("Sorry, the correct result is \"" 
                        + resultOfMethod + "\". try again!");
		}
	}

}

Now, here the questions. One last premise. I'm trying to learn to code properly, so i'd like to understand if my choices are correct. Here the question/doubts.

1 - in method checkAnswerInput() (which controls if the user has typed a number and not a letter),
there are two different implementations i've made to call back again the question, one with switch
and one with if else. I've heard that it's not good to use switch, but in this case i think
is the better solution. What do you think?
Are there other possible solutions to overcome this problem?

2 - In the four method that calls String methods (indexOfParamInt...() etc.) there is an if construct that repeats itself.
is there a possibility to use a method instead of four repetitions?
the point is that i need a return statement inside the method, only if the user typed a letter,
but if i create a method to handle the task, the return statemente works on the outside method,
not on the calling method. are there other possibilities to do this?

ok, for now that's it..
sorry if the questions seems dumb, probably they are.
if someone wants to give me feedback in general, they are more than welcome
thank you for the attention

[Winston Gutkowski]

Alex Derek wrote:i wanted to ask, to the holy and patients ones, to take a look at this code and help me, if possible, with some questions.

Well, it would help an awful lot if you could break up those enormous lines. It makes your thread (and code) very hard to read.
I'd do it myself, but you have tons of them. Just use the 'Edit' button, and the 'Preview' facility before you post.
(Tip: Don't put code and comments on the same line)

The rule here is:
80 characters max
(the SSCCE (←click) page actually recommends 62)
I suggest you re-read the UseCodeTags (←click) page carefully; and also the DontWriteLongLines one.

Thanks.

Winston

[Ivan Jozsef Balazs]

The comment and the method signature disagree.

    /* this method takes the input (a String) inserted from the user, creates a random number 
     * based on the length of the string inserted, apply indexOf(int ch) on the string and  
     * questions the user on the result. 
     */  
    public void indexOfParamInt()   
    { 

If the method really took an input String, it would rather look like this, but the void return type is not nice either:

    public void indexOfParamInt(String input) // ...

[Alex Derek]

Thank you for your reply.
I've tried to adjust a bit the question. I'm not sure it's ok.
If not, please tell me what i should improve.

@ Ivan, my comments were not that good, i've changed them, now they should be more clear.
The input string it's this:

 answerInput = user.getUserInput("What is the result of method \"indexOf(int ch)\"   
\n indexOf(" + firstInput.charAt(resultOfMethod)   
+") applied on your string?"); 

My expression was not right.
The program works so:

Please insert a word, letters and numbers allowed: <user typing> want a beer?</user typing>
What is the result of method "indexOf(int ch)"
indexOf( ) applied on your string? <user typing>0</user typing>
Sorry, the correct result is "4". try again!
What is the result of method "indexOf(int ch, int fromIndex)"
indexOf(n, 2) applied on your string? <user typing>2</user typing>
correct!
What is the result of method "indexOf(String str)"
indexOf(wa) applied on your string?<user typing> f</user typing> -> user inserted a letter,
not good, ask the question again
Sorry, but this method requests an integer as answer, so you have
to insert a number. Try again!
What is the result of method "indexOf(String str)"
indexOf(ant a) applied on your string?<user typing> 1</user typing>
correct!
What is the result of method "indexOf(String str, int fromIndex)"
indexOf(, 2) applied on your string?<user typing> 0</user typing>
Sorry, the correct result is "2". try again!



@ Winston, i've tried to clear the code. I'm sorry but it's still more than a hundred lines.

[Winston Gutkowski]

Alex Derek wrote:@ Winston, i've tried to clear the code. I'm sorry but it's still more than a hundred lines.

Well, thanks for the effort, I'll look it over thoroughly and give you any more comments as they come to me (probably tomorrow, I'm afraid; it's nearly 11pm here), but for future reference you may want to look at the SSCCE (←click) page. It's an excellent guide to how to provide code to forums like this.

However, one thing that does spring to mind immediately is that when writing a program - especially one that is arranged in "methods" (ie String methods) like yours:

1. Don't write more than about 10 lines at a time without compiling.

2. Break up each "method" into its own method (or class), and don't even start on a new one until you are absolutely sure that the current one works completely - ie, you shouldn't suddenly be finding errors when you're working on your 4th method.

Since the pattern for each "method" (actually, from what you were saying, a "method lesson") is the same (take string→take parameter(s)→take user's answer→check answer against actual result), writing and testing each one individually might have pointed you in a different direction for constructing your program. For example:

public interface StringMethodLesson {
   public void readString(Scanner s);
   public void readParameters(Scanner s);
   public void readAnswer(Scanner s);
   public void checkAnswer();
}

which you then implement for each String method you want to create a "lesson" for.

Unfortunately, you appear to have worked on all of them at once, which is why you're worried about dispatch statements like if...else and switch. You may still end up using one, but when you find them cropping up a lot in your programs, it's usually an indication that you haven't properly decomposed your problem.

BTW, the above is just ONE possibility; there are many others. You could also eliminate the Scanner parameter by simply passing it to each "lesson" object when you create it.

HIH

Winston

[Alex Derek]

Winston, thank you very much!
One thing is to study the concepts on OO, another is to learn to apply them,
and in this moment that's my issue.

I'll review all the code of my class and rethink it with your suggestion.
Thank you again