Validate String from user input - Help!

[jakubee]

Hello everyone,
This is my first post in here :)
Need a help with v. simple exercise.
I need to ask user to input 10 objects of type Product (String name, Double price).
I manage to done this. What i need to do now is to validate this inputs!
I want to get an console error message when user does type nothing and/or type an number instead of name (String). And same for price, when user enters a String instead of number (Double).
This is what i got so far (NOT MUCH) :

try {
		BufferedReader input = new BufferedReader(new InputStreamReader(System.in) );
		Product[] product = new Product[10];
		System.out.println("Please enter 10 product names and their price");
		
			for (int i = 0; i < product.length; i++) {
				System.out.println("Product name: ");
				String name = input.readLine();
				
				while (name.isEmpty())
					if (name == "" || name.length() == 0) {
					System.out.println("Must type a NAME!");
				}
				
				System.out.println("Prosuct price: ");
				Double price = Double.parseDouble(input.readLine());
				
				product[i] = new Product(name, price);
		}
	
		/**for (int i = 0; i < 11; i ++) {
		String name = bf.readLine();
		if(name == null || name.length() == 0) {
			System.out.println("MUST type a name!");
			for(int y = 0; y <name.length();y++) {
			if (!Character.isLetter(name.charAt(i)))
				System.out.println("Must be a String!");
			}
		}
		}**/
			System.out.println("Sort them by name or price? Enter n for name and p for price! ");
			
			String n = "n", p = "p";
			
			ProductNameComparator compByName = new ProductNameComparator();
			if (input.readLine() == n) {
				for(int i = 0; i < product.length; i++ ) {
					Arrays.sort(product, compByName);
				}
				for (int i = 0; i < product.length; i++) {
					System.out.println(product[i].getName() + ", " + product[i].getPrice());
			}
			}

Do i need to use a do/while loop?
Is it better to use Scanner in this case??

Thanks a lot with advance!

[DavidKroukamp]

Hello everyone, This is my first post in here :) Need a help with v. simple exercise. I need to ask user to input 10 objects of type Product (String name, Double price). I manage to done this. What i need to do now is to validate this inputs! I want to get an console error message when user does type nothing and/or type an number instead of name (String). And same for price, when user enters a String instead of number (Double). This is what i got so far (NOT MUCH) :

try {
		BufferedReader input = new BufferedReader(new InputStreamReader(System.in) );
		Product[] product = new Product[10];
		System.out.println("Please enter 10 product names and their price");
		
			for (int i = 0; i < product.length; i++) {
				System.out.println("Product name: ");
				String name = input.readLine();
				
				while (name.isEmpty())
					if (name == "" || name.length() == 0) {
					System.out.println("Must type a NAME!");
				}
				
				System.out.println("Prosuct price: ");
				Double price = Double.parseDouble(input.readLine());
				
				product[i] = new Product(name, price);
		}
	
		/**for (int i = 0; i < 11; i ++) {
		String name = bf.readLine();
		if(name == null || name.length() == 0) {
			System.out.println("MUST type a name!");
			for(int y = 0; y <name.length();y++) {
			if (!Character.isLetter(name.charAt(i)))
				System.out.println("Must be a String!");
			}
		}
		}**/
			System.out.println("Sort them by name or price? Enter n for name and p for price! ");
			
			String n = "n", p = "p";
			
			ProductNameComparator compByName = new ProductNameComparator();
			if (input.readLine() == n) {
				for(int i = 0; i < product.length; i++ ) {
					Arrays.sort(product, compByName);
				}
				for (int i = 0; i < product.length; i++) {
					System.out.println(product[i].getName() + ", " + product[i].getPrice());
			}
			}

Do i need to use a do/while loop? Is it better to use Scanner in this case??

Thanks a lot with advance!

The first is i wouldnt use '==' primitive comparator for strings rather use the equals() method or else the if statement wont execute i.e:

if ("".equals(name) || name.length() == 0) {

other then that i cant help much because i cant test the code, but i'd suggest using a try catch around statements like"sc.nextDouble();" etc :

Scanner sc = new Scanner(System.in);
            System.out.println("Type a double. i.e 7.89 or for error any string");
        try {
            sc.nextDouble();
        } catch (Exception e) {
            System.out.println("You didnt enter a double");
        }

therefore an exception will be thrown if a string is entered instead of an double, however you could read all input in as a string by nextLine() and then cast them to their correct objects i.e String->Double, and catch any exception that occurs during the format-NumberFormatException

[jakubee]

thing is that when i run the app and enter nothing it asks me for a price instead of warning and going through the 'for loop'. i dont realy know how to overcome this.

[DavidKroukamp]

thing is that when i run the app and enter nothing it asks me for a price instead of warning and going through the 'for loop'. i dont realy know how to overcome this.

well also this is really not helping the situation:

while (name.isEmpty())//so every time the input has nothing
					if (name.equals("") || name.length() == 0) {//check if its equal to any of these??? but we're in a while loop thats only executing when input is empty
					System.out.println("Must type a NAME!");
				}

maybe a

while(name.hasNext())

or

while(name.hasNextLine())

or the real not good coding style of

while(!name.isEmpty())

[jakubee]

Tried them all, non of them helps.

[DavidKroukamp]

Tried them all, non of them helps.

to be honest thats not helpful, how must i know if you implemented it correctly etc... however if you want more help i would ask you post you entire working code... so that others may test is and see exactly where and what should change...