Nehtdx

Is exact Kanji stroke length important?

What does "I’d sit this one out, Cap," imply or mean in the context?

Class Action - which options I have?

Risk of infection at the gym?

Did Dumbledore lie to Harry about how long he had James Potter's invisibility cloak when he was examining it? If so, why?

Lay out the Carpet

How to Reset Passwords on Multiple Websites Easily?

For a non-Jew, is there a punishment for not observing the 7 Noahide Laws?

How did Arya survive the stabbing?

Unreliable Magic - Is it worth it?

Why didn't Theresa May consult with Parliament before negotiating a deal with the EU?

Customer Requests (Sometimes) Drive Me Bonkers!

What is the best translation for "slot" in the context of multiplayer video games?

How do I go from 300 unfinished/half written blog posts, to published posts?

CREATE opcode: what does it really do?

Do the temporary hit points from Reckless Abandon stack if I make multiple attacks on my turn?

Why, precisely, is argon used in neutrino experiments?

How does buying out courses with grant money work?

Are student evaluations of teaching assistants read by others in the faculty?

Sort a list by elements of another list

Closest Prime Number

Do sorcerers' subtle spells require a skill check to be unseen?

How does the UK government determine the size of a mandate?

How do scammers retract money, while you can’t?

Why can methods be overriden but attributes can't?

What is reflection and why is it useful?What is a serialVersionUID and why should I use it?Understanding Python super() with __init__() methodsHow to know if an object has an attribute in PythonWhy is subtracting these two times (in 1927) giving a strange result?Why don't Java's +=, -=, *=, /= compound assignment operators require casting?Why is char[] preferred over String for passwords?Why is it faster to process a sorted array than an unsorted array?Why not inherit from List<T>?Why is printing “B” dramatically slower than printing “#”?

12

6

I have a class

public class A 
 public String attr ="A attribute";
 public void method() 
 System.out.println(this+" , "+this.attr);
 
 public String toString() 
 return("Object A");
 

and another class that inherits from it

public class B extends A
 public String attr = "B attribute";
 public void method() 
 super.method();
 
 public String toString() 
 return("Object B");
 

Note that the method() of B is simply a wrapper for method() of A.

When I run the following code

B b = new B();
b.method();

I get Object B , A attribute as output which means that, this and this.attr accessed different things. Why is that the case?

Shouldn't System.out.println(this) refer to the toString() method of class A ?

java inheritance attributes this shadowing

share|improve this question

edited 4 hours ago

Solomon Ucko

7772822

asked 10 hours ago

Noah BishopNoah Bishop

1036

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  A modern IDE will have the possibility to show a warning on the second definition of attr that it 'shadows' a similarly named field of a superclass.
  
  – Mark Jeronimus
  9 hours ago
  

  
  
  
  

add a comment | 

12

6

I have a class

public class A 
 public String attr ="A attribute";
 public void method() 
 System.out.println(this+" , "+this.attr);
 
 public String toString() 
 return("Object A");
 

and another class that inherits from it

public class B extends A
 public String attr = "B attribute";
 public void method() 
 super.method();
 
 public String toString() 
 return("Object B");
 

Note that the method() of B is simply a wrapper for method() of A.

When I run the following code

B b = new B();
b.method();

I get Object B , A attribute as output which means that, this and this.attr accessed different things. Why is that the case?

Shouldn't System.out.println(this) refer to the toString() method of class A ?

java inheritance attributes this shadowing

share|improve this question

edited 4 hours ago

Solomon Ucko

7772822

asked 10 hours ago

Noah BishopNoah Bishop

1036

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  A modern IDE will have the possibility to show a warning on the second definition of attr that it 'shadows' a similarly named field of a superclass.
  
  – Mark Jeronimus
  9 hours ago
  

  
  
  
  

add a comment | 

I have a class

public class A 
 public String attr ="A attribute";
 public void method() 
 System.out.println(this+" , "+this.attr);
 
 public String toString() 
 return("Object A");
 

and another class that inherits from it

public class B extends A
 public String attr = "B attribute";
 public void method() 
 super.method();
 
 public String toString() 
 return("Object B");
 

Note that the method() of B is simply a wrapper for method() of A.

When I run the following code

B b = new B();
b.method();

I get Object B , A attribute as output which means that, this and this.attr accessed different things. Why is that the case?

Shouldn't System.out.println(this) refer to the toString() method of class A ?

java inheritance attributes this shadowing

share|improve this question

edited 4 hours ago

Solomon Ucko

7772822

asked 10 hours ago

Noah BishopNoah Bishop

1036

public class A 
 public String attr ="A attribute";
 public void method() 
 System.out.println(this+" , "+this.attr);
 
 public String toString() 
 return("Object A");
 

public class B extends A
 public String attr = "B attribute";
 public void method() 
 super.method();
 
 public String toString() 
 return("Object B");
 

B b = new B();
b.method();

share|improve this question

edited 4 hours ago

Solomon Ucko

7772822

asked 10 hours ago

Noah BishopNoah Bishop

1036

share|improve this question

edited 4 hours ago

Solomon Ucko

7772822

asked 10 hours ago

Noah BishopNoah Bishop

1036

edited 4 hours ago

Solomon Ucko

7772822

edited 4 hours ago

Solomon Ucko

7772822

asked 10 hours ago

Noah BishopNoah Bishop

1036

asked 10 hours ago

Noah BishopNoah Bishop

1036

1 Answer
1

active

oldest

votes

12

By declaring a method with a same name as parent class, you override it, that is, replace the original behaviour. But if you declare a field with a same name, you effectively hide it, making it inaccessible from that subclass, but only by super.field. See oracle docs on variable hiding, as well as using the keyword super. Note that it is not recommended to use variable hiding, as it creates exactly the kind of confusion you're experiencing.

By calling super.method(), printing this results in calling the toString method, which was in fact overridden - so that's the reason why it prints "Object B", as you've called the method on an instance of B. But the this in this.attr actually refers to the parent object, as you're calling the method from the parent class (by super.method()).

share|improve this answer

edited 10 hours ago

answered 10 hours ago

Ondra K.Ondra K.

630720

add a comment | 

Your Answer

StackExchange.ifUsing("editor", function ()
StackExchange.using("externalEditor", function ()
StackExchange.using("snippets", function ()
StackExchange.snippets.init();
);
);
, "code-snippets");

StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "1"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);

else
createEditor();

);

function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);



);

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name

Email

Required, but never shown

StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f55380016%2fwhy-can-methods-be-overriden-but-attributes-cant%23new-answer', 'question_page');

);

Post as a guest

Name

Email

Required, but never shown

12

By declaring a method with a same name as parent class, you override it, that is, replace the original behaviour. But if you declare a field with a same name, you effectively hide it, making it inaccessible from that subclass, but only by super.field. See oracle docs on variable hiding, as well as using the keyword super. Note that it is not recommended to use variable hiding, as it creates exactly the kind of confusion you're experiencing.

By calling super.method(), printing this results in calling the toString method, which was in fact overridden - so that's the reason why it prints "Object B", as you've called the method on an instance of B. But the this in this.attr actually refers to the parent object, as you're calling the method from the parent class (by super.method()).

share|improve this answer

edited 10 hours ago

answered 10 hours ago

Ondra K.Ondra K.

630720

add a comment | 

12

By declaring a method with a same name as parent class, you override it, that is, replace the original behaviour. But if you declare a field with a same name, you effectively hide it, making it inaccessible from that subclass, but only by super.field. See oracle docs on variable hiding, as well as using the keyword super. Note that it is not recommended to use variable hiding, as it creates exactly the kind of confusion you're experiencing.

By calling super.method(), printing this results in calling the toString method, which was in fact overridden - so that's the reason why it prints "Object B", as you've called the method on an instance of B. But the this in this.attr actually refers to the parent object, as you're calling the method from the parent class (by super.method()).

share|improve this answer

edited 10 hours ago

answered 10 hours ago

Ondra K.Ondra K.

630720

add a comment | 

By declaring a method with a same name as parent class, you override it, that is, replace the original behaviour. But if you declare a field with a same name, you effectively hide it, making it inaccessible from that subclass, but only by super.field. See oracle docs on variable hiding, as well as using the keyword super. Note that it is not recommended to use variable hiding, as it creates exactly the kind of confusion you're experiencing.

By calling super.method(), printing this results in calling the toString method, which was in fact overridden - so that's the reason why it prints "Object B", as you've called the method on an instance of B. But the this in this.attr actually refers to the parent object, as you're calling the method from the parent class (by super.method()).

share|improve this answer

edited 10 hours ago

answered 10 hours ago

Ondra K.Ondra K.

630720

share|improve this answer

edited 10 hours ago

answered 10 hours ago

Ondra K.Ondra K.

630720

answered 10 hours ago

Ondra K.Ondra K.

630720

answered 10 hours ago

Ondra K.Ondra K.

630720