MOOC PART 5

[haughty kestrel]

This is an example problem under Comparing the equality of objects (equals) and I have an doubt.

If it returns false already how does it go to the next part

Help?

[dapper bay]

<@&987246399047479336> please have a look, thanks.

[haughty kestrel]

@burnt star

[hexed drum]

@haughty kestrel by the if condition not evaluating to true.

[surreal blade]

Look at the condition

[surreal blade]

Don't mention random helpers please

[haughty kestrel]

i was doing the course with hhim

so i pinged him

out of alliance

:p

[surreal blade]

ah

[haughty kestrel]

so yeah

dosent that mean

that if it is not simple date go away

then it says to convert it into simple date

[hexed drum]

Yes?

[haughty kestrel]

well if it goes away how does it reach the next part?

isnt it supposed to return false

[hexed drum]

By being a SimpleDate.

[burnt star]

yeah its fine

dont worry

[haughty kestrel]

see if it return false the whole method is done right

isnt it supposed to return true/false

[surreal blade]

if it isn't a SimpleDate, why would you want it to reach the next part ?

[burnt star]

it only proceeds through the first if statement if the compared object is not an instance of the SimpleDate class

[haughty kestrel]

but if it is simpledate why convert it into simpel date again

[burnt star]

which is the check, as everyone else mentioned

[hexed drum]

No, it's not because it's a SimpleDate that it's the same date. Hence the further checks.

[surreal blade]

Because you need to, well kinda

[burnt star]

because you retrieve that data as an Object type

and you cannot access to the data inside directly without converting it to what it was made as

[haughty kestrel]

second loop we use it to check for simple date if it is simpeldate why we converting it again to simple date

[burnt star]

such as, if you have a "String name" variable inside this compared object, without changing the type back to what it was you cannot reach the name variable

[haughty kestrel]

so you convert it and retrieve it agian

[surreal blade]

Because while you, you know that it is a SimpleDate, java doesn't

[burnt star]

yes, because you want to compare the other data inside this compared object in order to check if this object is exactly identical to the one that you are comparing it

such as, we can both be Students

but have different names

it first checks if you are even a student

[haughty kestrel]

so you need to convert it into its own type again to get the data in it?

[surreal blade]

yes

[haughty kestrel]

werid

wonder why

[burnt star]

if you are indeed a student, the first if block doesn't activate, but if you are a teacher the first if block stops the program

[haughty kestrel]

fix java alathreon

[surreal blade]

It's logic

[haughty kestrel]

no logic

[surreal blade]

It's already fixed

[haughty kestrel]

java dumb add ai to it

[burnt star]

if you are a student it continues to check if you have the same name and such, but in order to check your name it needs to change you from Object, back to Student

because the name variable itself is in class Student

thats roughly the idea

[haughty kestrel]

hmm

[surreal blade]

The if just tells java if it should go in its branch or not
The variable type won't magically change

[haughty kestrel]

just wanted to knwo why we switch it to its own type after knwing its the type we want

[surreal blade]

Because we can ?

[burnt star]

I think the reason why it comes as Object and not Student is because the classes could be typecasted to something else that they inherit one way or another

[haughty kestrel]

animal cat we know but we again define it under animal

[haughty kestrel]

we can nuke the world?

[surreal blade]

you misunderstand

[burnt star]

such as, you could cast a Student, Teacher, President, Janitor to Human if you implemented it

[haughty kestrel]

i think its deeper into java smth

hmm

[burnt star]

so its better to just take it as Object

because Object is implicitly extended by all other, well, objects

[haughty kestrel]

aight

stop right here

can we start from the start?

[burnt star]

I didn't word that well

XD

[surreal blade]

You want to go to the toilet
you have an if(!isToiletFree()) return;
but if it doesn't return, it means that you know that you can go to the toilet, but you still need to gotToToilet();

The if just gives you info that you can do it

then you use this info

[haughty kestrel]

my only doubt is why the second comparison after have checked it is the type we want

[surreal blade]

to do what you want

[haughty kestrel]

like we know its a cat at the start by using the if

[surreal blade]

wdym, which comparaison ?

[haughty kestrel]

but why we making it a cat again

gimme a sec

[surreal blade]

We are making it a cat once

[burnt star]

your name is mirza, mine is hirayui, how can the program know that we are not the same user without comparing something that we have different, if we are both users?

[surreal blade]

@haughty kestrel

[surreal blade]

The if just gives you information, it doesn't change it into a cat

[surreal blade]

see this

[haughty kestrel]

isnt it alr a cat or does it change its type when it gets inputted as an object

does it get changed to object?

[surreal blade]

It was always a cat

[haughty kestrel]

so when we give it as an parameter it turns into object type?

and we need to make it simple date again?

[surreal blade]

but you first need to check if it is actually a cat
and if it is, you tell java, "well that's a cat"

[burnt star]

because the parameter's type is Object

yes

[haughty kestrel]

bring the cat as an dinasour check if it is a cat orginally if yes then convert into a cat?

damn

i get it now

compare the object type date into

simpledate type date

damn i annoyed yall

[burnt star]

dw

[haughty kestrel]

but...

if its imported as object type then how we seeing the compared type

whatever

[burnt star]

that has to do with inheritance I think

[haughty kestrel]

oo

[burnt star]

did you learn anything about it?

[haughty kestrel]

not yet

but in uniyes

inherit the things from diff clases

[hexed drum]

instanceof

[haughty kestrel]

i remember it kinda

[haughty kestrel]

bro writes instanceof as if iam an expert in java and i can understand what he means

[hexed drum]

1. let's stay polite
2. It's documented in the course, and the keyword does kind of say it. instance of. To put it alternatively: what do you think mirza instanceof Human results in?

[burnt star]

so as an example off the top of my head, if you have a class Teacher that implements Employee, you can both do Teacher mirza = new Teacher(); and Employee mirza = new Teacher();

but the object saved in the memory with an id is still a new Teacher();

even though you can also put it in a variable with the type Employee

so if I am not mistaken, instanceOf just checks what is saved in the memory for that variable, therefore it can see and compare what it actually was

[haughty kestrel]

that iam a human

[burnt star]

if that makes sense to you

[haughty kestrel]

sure

[hexed drum]

So you would be passed in as an Object in the above example. The same logic applies.

[burnt star]

but this is my own interpretation

[haughty kestrel]

thx

[burnt star]

simon do you think my example is bad, mistaken?

[hexed drum]

I think I'd have started by explaining what instanceof does, since there the confusion seemingly started.

[surreal blade]

@haughty kestrel variables have a name and type
the type is like a label, which hints at what is inside the variable
even if you check the actual object inside the variable, the type won't magically change, you need to explicitly create a new variable with the correct type

[surreal blade]

@haughty kestrel here

[haughty kestrel]

public class Person {

    private String name;
    private int age;
    private int weight;
    private int height;

    // constructors and methods


    public boolean equals(Object compared) {
        // if the variables are located in the same position, they are equal
        if (this == compared) {
            return true;
        }

        // if the compared object is not of type Person, the objects are not equal
        if (!(compared instanceof Person)) {
            return false;
        }

        // convert the object into a Person object
        Person comparedPerson = (Person) compared;

        // if the values of the object variables are equal, the objects are equal
        if (this.name.equals(comparedPerson.name) &&
            this.age == comparedPerson.age &&
            this.weight == comparedPerson.weight &&
            this.height == comparedPerson.height) {
            return true;
        }

        // otherwise the objects are not equal
        return false;
    }

[surreal blade]

Also don't omit @Override

    @Override
    public boolean equals(Object compared) {

Also

any

if(foo) {
 return true;
} else {
  return false
}

can be simplified into

return foo;

So instead of this

        if (this.name.equals(comparedPerson.name) &&
            this.age == comparedPerson.age &&
            this.weight == comparedPerson.weight &&
            this.height == comparedPerson.height) {
            return true;
        }

        // otherwise the objects are not equal
        return false;

You can write this

        return this.name.equals(comparedPerson.name) &&
            this.age == comparedPerson.age &&
            this.weight == comparedPerson.weight &&
            this.height == comparedPerson.height;

    public boolean equals(Object compared) {
        // if the variables are located in the same position, they are equal
        if (this == compared) {
            return true;
        }

        // if the compared object is not of type Person, the objects are not equal
        if (!(compared instanceof Person comparedPerson)) {
            return false;
        }

        // if the values of the object variables are equal, the objects are equal
        if (this.name.equals(comparedPerson.name) &&
            this.age == comparedPerson.age &&
            this.weight == comparedPerson.weight &&
            this.height == comparedPerson.height) {
            return true;
        }

        // otherwise the objects are not equal
        return false;
    }

Also you can do this

You can instanceof and cast at the same time