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Java Community | Help. Code. Learn.•12mo ago

what’s the point of the this. keyword in Java?

So I’m learning Java currently and I just learned about ‘this’ but I don’t quite get what the point of it is.. From what I read… it’s used by coders in order to not confuse the instance variables with their methods’ parameter variables and hence they use ‘this’ I also read that it is to take a reference of the instance variable. However what I don’t get it that can’t you just either use different parameter variable names in order to avoid the confusion? And why can’t I just write the instance variables name directly instead of using ‘this’, like it still works that way…? I also attached a picture on what I mean. In the picture, there is already a different parameter variable name, so there’s no confusion in that, and when it comes to initializing the instance variable, can’t I just do name = theName; Or return name; Instead of whatever they have in the picture?

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62 Replies

JavaBot•12mo ago

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noComment | Kez•12mo ago

this makes sure you refer to the instance variable.

applesandhoneyOP•12mo ago

But can’t the same thing be accomplished with the way I wrote instead? Or would there be errors?

noComment | Kez•12mo ago

This should work

applesandhoneyOP•12mo ago

I’m free to criticism in my technique btw, I just want to learn the point of this So both ways work?

noComment | Kez•12mo ago

We don’t only use the keyword this in the context of constructors It is a general tool to access the instance of the object we are handeling

applesandhoneyOP•12mo ago

But so can I also not access it just by calling it without the this?

JavaBot•12mo ago

https://tryitands.ee/

noComment | Kez•12mo ago

but yes

applesandhoneyOP•12mo ago

No like that’s how I’ve been writing code till now which is why I’m lost Like without the this

noComment | Kez•12mo ago

since there is no way the interpreter can misinterpret what you mean the thiscall will be implicit it is possible to write it like you did but its not a good practice since we like our standard functions to be... standardized

applesandhoneyOP•12mo ago

standardized is like a general style of writing code right?

noComment | Kez•12mo ago

yes

applesandhoneyOP•12mo ago

so basically it’s just for sophistication?

noComment | Kez•12mo ago

we write getters and setters and constructors as standardized as possible so we see if they are right on the first glance even if its not our code not our code can also be our code from like a few weeks back 😄 we can also use this for other stuff by the way you can use this to call a method within the current class for example or use it to call another constructor from a constructor

applesandhoneyOP•12mo ago

that makes sense

noComment | Kez•12mo ago

the this keyword in quite useful in general

applesandhoneyOP•12mo ago

waittt so that gets a reference of the method then?!

noComment | Kez•12mo ago

its handy to have something that can point to "itself"

public class MyClass {
    // Instance variable
    private String name;

    // Constructor
    public MyClass(String name) {
        this.name = name;
    }

    // Method to print name
    public void printName() {
        System.out.println("Name: " + this.name);
    }

    // Method to call another method using 'this'
    public void callPrintName() {
        this.printName();
    }
}

public class Main {
    public static void main(String[] args) {
        MyClass obj = new MyClass("John");
        obj.callPrintName();  // This will print "Name: John"
    }
}

public class MyClass {
    // Instance variable
    private String name;

    // Constructor
    public MyClass(String name) {
        this.name = name;
    }

    // Method to print name
    public void printName() {
        System.out.println("Name: " + this.name);
    }

    // Method to call another method using 'this'
    public void callPrintName() {
        this.printName();
    }
}

public class Main {
    public static void main(String[] args) {
        MyClass obj = new MyClass("John");
        obj.callPrintName();  // This will print "Name: John"
    }
}

here are 3 use cases for this

applesandhoneyOP•12mo ago

thank you for sending this!

JavaBot•12mo ago

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applesandhoneyOP•12mo ago

sry i have one more question

noComment | Kez•12mo ago

Ask away

applesandhoneyOP•12mo ago

basically a reference of something doesn’t access that actual something right? so if im using this for a method or variable, does that mean i am not accessing the actual method or variable?

noComment | Kez•12mo ago

You are Java is a bit weird in the way it implements it Do you know what pass by reference and pass by value means?

applesandhoneyOP•12mo ago

my teacher mentioned it but we haven’t learned it yet so whether i do it by reference or actual, i still access the same method/variable?

noComment | Kez•12mo ago

See, Java is pass by value, for primitive types like int or char that means only the value of a variable int is passed into a method in a method call. So changing that value doesn’t affect the original variable. It’s different for objects tho. The value that is passed in case of an object is the reference to that object. So if I change the value of a complex type instead the value would also change for the original variable What do you mean by “by reference or actual” this is always a reference to that object, not the value inside that object.

applesandhoneyOP•12mo ago

so for primitive the original variables can change and for object they can change but they hold the reference, so the original variable is still the same?

noComment | Kez•12mo ago

You got it backwards

applesandhoneyOP•12mo ago

sorry i mean that whether I use this or not oh

noComment | Kez•12mo ago

The reference is like a link to the original object

applesandhoneyOP•12mo ago

so is it primitive variable:- original variable cannot change object variable:- original variable still doesn’t change but the object uses a reference of the original variable

noComment | Kez•12mo ago

the original values inside of an object can change let me try to write a quick example

applesandhoneyOP•12mo ago

okay tysm

noComment | Kez•12mo ago

./run

public class Main {
    public static void main(String[] args) {
        int num = 10;
        System.out.println("Before: " + num);
        changeValue(num);
        System.out.println("After: " + num);
    }

    public static void changeValue(int num) {
        num = 20;
    }
}

public class Main {
    public static void main(String[] args) {
        int num = 10;
        System.out.println("Before: " + num);
        changeValue(num);
        System.out.println("After: " + num);
    }

    public static void changeValue(int num) {
        num = 20;
    }
}

I Run Code•12mo ago

Here is your java(15.0.2) output @noComment | Kez

Before: 10
After: 10

Before: 10
After: 10

noComment | Kez•12mo ago

./run

public class Main {
    public static void main(String[] args) {
        int[] arr = {10};
        System.out.println("Before: " + arr[0]);
        changeValue(arr);
        System.out.println("After: " + arr[0]);
    }

    public static void changeValue(int[] arr) {
        arr[0] = 20;
    }
}

public class Main {
    public static void main(String[] args) {
        int[] arr = {10};
        System.out.println("Before: " + arr[0]);
        changeValue(arr);
        System.out.println("After: " + arr[0]);
    }

    public static void changeValue(int[] arr) {
        arr[0] = 20;
    }
}

I Run Code•12mo ago

Here is your java(15.0.2) output @noComment | Kez

Before: 10
After: 20

Before: 10
After: 20

noComment | Kez•12mo ago

Here you can see the two cases first we see what happens to a primitive value passed into a method the value of num stays the same before and after we changed "num" in the changeValue method the value of the array however does change because not the value of the array is passed to the method but the reference to that array ./run

public class Main {
    public static void main(String[] args) {
        int[] arr = {10};
        System.out.println(arr);
    }
}

public class Main {
    public static void main(String[] args) {
        int[] arr = {10};
        System.out.println(arr);
    }
}

I Run Code•12mo ago

Here is your java(15.0.2) output @noComment | Kez

[I@4f51b3e0

[I@4f51b3e0

noComment | Kez•12mo ago

here we see what is the content of the variable arr it is not the content of the array but the reference to the array. that is what that random stuff means.

applesandhoneyOP•12mo ago

but here it’s instead passing 10 that is in num but not the variable num to which we could assign 20 so how would it change num from 10 to 20?

noComment | Kez•12mo ago

what? what do you mean?

applesandhoneyOP•12mo ago

like yk in changeValue(num), wouldn’t it be passing 10 instead? since num = 10, when we do changeValue(num), it’s passing 10 to changeValue right?

noComment | Kez•12mo ago

it is. It is literally just passing the content of the variable to the method, not the reference to the variable.

applesandhoneyOP•12mo ago

okay

applesandhoneyOP•12mo ago

No description

applesandhoneyOP•12mo ago

in the part where it says num = n, that’s assigning n to num’s reference?

noComment | Kez•12mo ago

no here you are accessing a static member of a class and change that directly this has an implicit thisagain this.num = n; num doesn't have a reference (i think) since it is a primitive type

applesandhoneyOP•12mo ago

implicit as in it just happens without me having to code it?

noComment | Kez•12mo ago

yes there are two types of storage in java heap and stack on the heap there are your primitive types like ints and all that on the stack are your complex types so everything that is derived from object

applesandhoneyOP•12mo ago

sorry im being so repetitive but this just gets the reference of that variable right?

noComment | Kez•12mo ago

on the heap there can also be references to the stack there is NO REFERENCE for primitive types

applesandhoneyOP•12mo ago

but then how does ‘this’ work then because it gets the reference?

noComment | Kez•12mo ago

we dont need a reference since we are accessing the varbiable itself. it is a member of the class.

applesandhoneyOP•12mo ago

so it depends on whether ‘this’ is accessing the variable itself or the reference? also im so sorry it’s like im getting it then I don’t get it then I get it then I don’t

noComment | Kez•12mo ago

thisis referencing the current instance of the class Main, so the object we are dealing with at the moment

applesandhoneyOP•12mo ago

okay it’s making sense again now hope it stays like that in my brain

noComment | Kez•12mo ago

hope so too 🙂

applesandhoneyOP•12mo ago

thank you very much though!

JavaBot•12mo ago

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JavaBot•12mo ago

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