Difference between again == "y"; and again.equals("y");

[sandman18and5]

Hey all,

This is my first post, so be gentle :P

So, I was following a tutorial and it prompted me to make a grade telling machine based on numeric input from the keyboard from java.util.Scanner

import java.util.*;
import java.io.*;

public class GradeCalculator {

public static void main(String[] args){

String again = "y";
while (again.equals("y")){
System.out.println("What is your numeric grade? ");

Scanner kbReader = new Scanner(System.in);

double grade = kbReader.nextDouble();
if (grade == 100){
System.out.println("PERFECT SCORE!\nWant to input another grade? ");
again = kbReader.next();
System.out.println(again == "y");
System.out.println(again.equals("y"));
} else if (grade>90 && grade < 100){
System.out.println("you get an A\nWant to input another grade? ");
again = kbReader.next();


when I ran it and entered 100 as the numeric grade, System printed this:
What is your numeric grade?
100
PERFECT SCORE!
Want to input another grade?
y
false
true
What is your numeric grade?

Why does again == "y"; return false?

any thoughts would be appreciated.

[eRaaaa]

Java: ==, .equals(), compareTo(), and compare()

[sandman18and5]

Thanks, eRaaaa,

That helped but that leaves me confused about the function of the == operator.

The site says:
This is true only if name is a reference to the same object that "Mickey Mouse" refers to. This will be false if the String in name was read from input or computed (by putting strings together or taking the substring), even though name really does have exactly those characters in it.

the second sentence explains my situation, but in the first sentence, what does it mean to reference the same object that "Mickey Mouse" refers to?

Thanks!

[awinston]

what does it mean to reference the same object that "Mickey Mouse" refers to?

2 variables have to literally reference the exact same object. For example:

JButton button1 = new JButton();
JButton button2 = button1;

In this case, button2 references the same object that is referenced by button1. There is only 1 JButton, as opposed to this example:

JButton button1 = new JButton();
JButton button2 = new JButton();

where 2 JButtons are created. Although the 2 JButtons have the same characteristics, they are still 2 separate objects.

[Tolls]

what does it mean to reference the same object that "Mickey Mouse" refers to?

Thanks!

String mm = "Mickey Mouse";

This will result in a String object in the String literal pool, referenced by the variable 'mm'.

String nn = mm;

This will give the variable 'nn' the same value as 'mm'. That value is the reference to the object in the literal pool.

String oo = new String("Mickey Mouse");

This will, at run time, create a new String object on the heap and 'oo' will reference it.
nn == mm as the references are the same.
oo != mm as the references are different.

[sandman18and5]

Thanks guys, that was really helpful!