Question

Why does this code not work even when typing in the correct product code? It always gives me the error message even though im typing one of the 3 correct product codes.

String[] product_code= new String[3];
String[] product_name= new String[3];
// String[] product_description = new String[3];

int[] quantity = new int[3];
double[] price = new double[3];
double[] itemTotal = new double[3];
double subTotal = 0, salesTax, total;
  
//getting all the needed inputs
for(int i = 0; i < 3; i++)
{
System.out.println("Input product code " + (i + 1) + ":");
product_code[i] = input.nextLine();
if(product_code[i]!= "100" || product_code[i]!= "101" || product_code[i]!= "102") {
    System.out.println("Error: Invalid Product Code please retry purchase ");
    break;
}

Answer 1

I probably thing you are trying to validate the condition using'==' instead of "equals" method.Because as you declared the product_code as String data type you must be using euals method to consider the condition evaluation against the product_code values.

In general both equals() and “==” operator in Java are used to compare objects to check equality but here are some of the differences between the two:

1. Main difference between .equals() method and == operator is that one is method and other is operator.
2. We can use == operators for reference comparison (address comparison) and .equals() method for content comparison. In simple words, == checks if both objects point to the same memory location whereas .equals() evaluates to the comparison of values in the objects.
3. If a class does not override the equals method, then by default it uses equals(Object o) method of the closest parent class that has overridden this method.

public class Test {     public static void main(String[] args)     {         Thread t1 = new Thread();         Thread t2 = new Thread();         Thread t3 = t1;         String s1 = new String("GEEKS");         String s2 = new String("GEEKS");         System.out.println(t1 == t3);         System.out.println(t1 == t2);         System.out.println(s1 == s2);         System.out.println(t1.equals(t2));         System.out.println(s1.equals(s2));     } }

Output:

true
false
false
false
true