Thread: While Loop Exit with String

This program works, although I don't understand how. I used }while ( !licenseNumber.equalsIgnoreCase ("quit") ); to exit the program when the user types quit but why doesn't it work when I write it like this licenseNumber != "quit"; doesn't it mean the samething basicly(I know the second one is case sensitive)

import java.util.Scanner;
 
public class TrafficFines
{
	public static void main(String[] args) 
	{
		Scanner input = new Scanner(System.in);
 
		String licenseNumber = "quit";
 
		System.out.println("Welcome to the Traffic Fine Reporting System.\n" +
				           "Please enter the requested data for each fine.");
 
 
 
		do
		{
 
		System.out.println("Enter the drivers license number - 'quit' to exit:");
		licenseNumber = input.nextLine();
 
 
		}while ( !licenseNumber.equalsIgnoreCase ("quit") );
 
 
	}// end method main
}// end class ConvertTemperature2

Not true, != and == are very useful for comparing if two objects are the same object, not if they contain the same data.

Yes, that's exactly why.

Say we had the two variables:

Object A and Object B.

The value contained by A and B are addresses to where some objects are.

If A==B, then they are pointing to the same object (can you see why?)

However, if A and B pointed to two different objects, A != B, no matter what data is actually contained in the two objects.

edit: beaten to it

That's one of the quirky ways java optimizes strings. Instead of creating multiple constant strings, sometimes the Java compiler will recognize that it already has that object and just assigns the same reference:

String s1 = "Test";
String s2 = "Test";
if (s1 == s2)
{
     System.out.println("s1 and s2 have the same reference!");
}

However, you can explicitly tell Java to create a new variable (and actually, the code above will fail sometimes because that optimization isn't used all the time)

String s1 = new String("Test");
String s2 = new String("Test");
 
if (s1 != s2)
{
    System.out.println("s1 and s2 have different references");
}