Calling up class methods

Question

I suffer problems understanding how to call up class methods from within my programs and would like to see further examples of coding and a lending hand with the problem below, program one ProductClass works out stock item lines of a product, the program then needs to ask for the StaticProduct Class(the second program attached) to check for a valid barcode length and for how many odds and even numbers are within it a valid barcode would be 5000127062092
I would very much appreciate some help:
* This is a program to Enter and check product codes and prices
* and give a summary of values at the end
* @author (Jeffrey Jones)
* @version (version 2 5th April 2003)
public class ProcessProduct
public static void main(String args[])
StaticProduct Product = new StaticProduct();
//declare variables
String manuf;
String name;
int sLength;
String p;
String barcode;
int price;
int quantity;
int totalPrice=0;
int transactions=1;
int totalQuantity=0;
int totalValue=0;
int averageCost=0;
//Input Details
System.out.print("Enter Product Manufacturer : ");
manuf = UserInput.readString();
//start of while loop checking for 0 to exit loop
while (!manuf.equals("0"))
System.out.print("Enter Product Name : ");
name = UserInput.readString();
System.out.print("Enter Bar Code : ");
barcode = UserInput.readString();
//check for invalid data
if (StaticProduct.isValidBarcode(barcode))
{barcode = new code();
                    p = new Product("manuf","name","quantity","price");
                    }//closing bracket of if
else
{//error handling
}//closing bracket of if
//check for quantity input and errors
System.out.print("Enter Quantity : ");
quantity = UserInput.readInt();
if (quantity<=0)
{ System.out.print(" Error, invalid value ");
System.exit(0);
}// check for invalid entries
System.out.print("Enter Price :");
price = UserInput.readInt();
//check for price input and errors
if (price<=0)
{ System.out.print(" Error, invalid value ");
}// check for invalid entries
//total price value
totalPrice=price*quantity;
//Output of correctly inputted data
System.out.println(manuf+":"+name+":"+barcode+":"+price);
System.out.println(quantity+" @ "+price+" = "+totalPrice);
//update variables quantities
//update total quantity
totalQuantity = (totalQuantity + quantity);
//keep count of total value
totalValue = (totalValue + totalPrice);
//keep count of totqal no of transactions
transactions = (transactions++);
//Input Details
System.out.print("Enter Product Manufacturer : ");
manuf = UserInput.readString();
}//closure of loop
//display final totals
System.out.println("Transactions: "+transactions);
System.out.println("Total quantity: "+totalQuantity);
System.out.println("Total value: "+totalValue);
System.out.println("Average Cost: "+totalValue/totalQuantity);
System.exit(0);
}//closing bracket input and output of data
}//end class
* Write a description of class StaticProduct here.
* @author Jeffrey Jones
* @version 1 1st April 2003
public class StaticProduct
* isValidBarcode method - to check for correct barcode and length
* @return boolean
public static boolean isValidBarcode(String barcode) {
barcode = new barcode();
// validateBarcode length
if ( barcode.length() != 13 ) {
System.out.println("Invalid barcode " + barcode + " not 13 characters");
return false;
}//if
for ( int i = 0; i < barcode.length(); i++ ){// Check every char a digit
if ( ! Character.isDigit( barcode.charAt(i) ) ){
System.out.println("Invalid barcode " + barcode + " not all digits");
return false;
}//if
}//endfor
int sum1 = 0; // Sum first + third + etc.
for ( int i = 0; i < barcode.length() - 1; i += 2 ){
sum1 += barcode.charAt(i) - '0';
}//endfor
int sum2 = 0; // Sum second + fourth + etc.
for ( int i = 1; i < barcode.length() - 1; i += 2 ){
sum2 += barcode.charAt(i) - '0';
}//endfor
int check = sum1 + 3 * sum2; // 1st sum + three times 2nd sum.
check = check % 10; // Remainder on division by 10.
if ( check != 0 ){
check = 10 - check;
}//endif
if (check != barcode.charAt(12) - '0'){
System.out.println("Invalid barcode " + barcode + " check digit error");
}//endif
return ( check == barcode.charAt(12) - '0' );
}//end isValidBarcode
public static void main(String[] argv) {
System.out.println(isValidBarcode("1234567890123"));
System.out.println(isValidBarcode("123"));
System.out.println(isValidBarcode(""));
System.out.println(isValidBarcode("5018374496652"));
}//end main
}//end class

Answer 1

Read through your text book or some java tutorials from this site to understand what classes are, what are methods, etc.
Your program is full of wrong initializations (as you rightly said you dont understand how to call up class method I would add that you dont understand how to call classes and what do they return e.g.
You have declared
String p;
then you go ahead and do this
p = new Product("manuf","name","quantity","price"); This is syntax for calling a class is this class returning a String? :s
Please go through the basics of Object Oriented Programming and then start with the coding part else you will face such very many difficulties and waste more time of yours in just coding with no results.
Look for the tutorials on this site and read through them and do example as given in them.