Why is this valid boolean b = new A() instanceof A; if A is an abstract class? [closed] The 2019 Stack Overflow Developer Survey Results Are InJava abstract class namingWhy should I declare a class as an abstract class?Why should a class be anything other than “abstract” or “final/sealed”?Java's Boolean class - why not an enum?Why 'List<E>' is an 'interface' but not 'abstract class'?Is there an alternative to instanceof when filtering a Java stream by class?What is the rule for nested loop code?Why override a static method of an abstract base class?When and why would you put a new method into an interface instead of an abstract base class?Avoiding instanceof vs abstract God Class. Do I have an alternative?
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Why is this valid boolean b = new A() instanceof A; if A is an abstract class? [closed]
The 2019 Stack Overflow Developer Survey Results Are InJava abstract class namingWhy should I declare a class as an abstract class?Why should a class be anything other than “abstract” or “final/sealed”?Java's Boolean class - why not an enum?Why 'List<E>' is an 'interface' but not 'abstract class'?Is there an alternative to instanceof when filtering a Java stream by class?What is the rule for nested loop code?Why override a static method of an abstract base class?When and why would you put a new method into an interface instead of an abstract base class?Avoiding instanceof vs abstract God Class. Do I have an alternative?
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I have trouble understanding why this boolean b = new A() instanceof A; is a valid statement and not boolean b = new A() instanceof A; and why the former is true knowing that A is an abstract class.
java object-oriented
asked Apr 5 at 1:19
Dr.StoneDr.Stone
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closed as off-topic by gnat, Bart van Ingen Schenau, David Arno, amon, Deduplicator Apr 5 at 10:06
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "Questions asking for assistance in explaining, writing or debugging code are off-topic here. These can be asked on Stack Overflow if they include the desired behavior, a specific problem or error, and the shortest code necessary to reproduce it in the question (see Minimal, Complete, and Verifiable Example)." – gnat, amon, Deduplicator
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I have trouble understanding why this boolean b = new A() instanceof A; is a valid statement and not boolean b = new A() instanceof A; and why the former is true knowing that A is an abstract class.
java object-oriented
asked Apr 5 at 1:19
Dr.StoneDr.Stone
192
New contributor
Dr.Stone is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
closed as off-topic by gnat, Bart van Ingen Schenau, David Arno, amon, Deduplicator Apr 5 at 10:06
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "Questions asking for assistance in explaining, writing or debugging code are off-topic here. These can be asked on Stack Overflow if they include the desired behavior, a specific problem or error, and the shortest code necessary to reproduce it in the question (see Minimal, Complete, and Verifiable Example)." – gnat, amon, Deduplicator
add a comment |
I have trouble understanding why this boolean b = new A() instanceof A; is a valid statement and not boolean b = new A() instanceof A; and why the former is true knowing that A is an abstract class.
java object-oriented
asked Apr 5 at 1:19
Dr.StoneDr.Stone
192
New contributor
Dr.Stone is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
I have trouble understanding why this boolean b = new A() instanceof A; is a valid statement and not boolean b = new A() instanceof A; and why the former is true knowing that A is an abstract class.
java object-oriented
java object-oriented
asked Apr 5 at 1:19
Dr.StoneDr.Stone
192
New contributor
Dr.Stone is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked Apr 5 at 1:19
Dr.StoneDr.Stone
192
New contributor
Dr.Stone is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked Apr 5 at 1:19
Dr.StoneDr.Stone
192
New contributor
Dr.Stone is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked Apr 5 at 1:19
Dr.StoneDr.Stone
192
asked Apr 5 at 1:19
Dr.StoneDr.Stone
192
192
New contributor
Dr.Stone is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Dr.Stone is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Dr.Stone is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
closed as off-topic by gnat, Bart van Ingen Schenau, David Arno, amon, Deduplicator Apr 5 at 10:06
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "Questions asking for assistance in explaining, writing or debugging code are off-topic here. These can be asked on Stack Overflow if they include the desired behavior, a specific problem or error, and the shortest code necessary to reproduce it in the question (see Minimal, Complete, and Verifiable Example)." – gnat, amon, Deduplicator
closed as off-topic by gnat, Bart van Ingen Schenau, David Arno, amon, Deduplicator Apr 5 at 10:06
This question appears to be off-topic. The users who voted to close gave this specific reason:
- "Questions asking for assistance in explaining, writing or debugging code are off-topic here. These can be asked on Stack Overflow if they include the desired behavior, a specific problem or error, and the shortest code necessary to reproduce it in the question (see Minimal, Complete, and Verifiable Example)." – gnat, amon, Deduplicator
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1 Answer
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The instanceof A has nothing to do with whether the statement is valid or not, so your question is simpler if you leave it off from both statements:
A a = new A() ;
A a = new A();
The second statement isn't valid because A is abstract and you can't call new on any abstract class. If you could instantiate it, it would be an instance of A, but you can't.
The first statement is valid because it creates an anonymous class that extends A. This anonymous class isn't abstract (assuming A doesn't define any abstract methods), and so it can be instantiated. It's an instance of A because all subclasses are instances of their parent classes, abstract or not. It's basically a shortcut for saying:
public class AnonymousNameIDontCareAbout extends A
A a = new AnonymousNameIDontCareAbout();
answered Apr 5 at 3:36
Karl BielefeldtKarl Bielefeldt
121k32217415
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
The instanceof A has nothing to do with whether the statement is valid or not, so your question is simpler if you leave it off from both statements:
A a = new A() ;
A a = new A();
The second statement isn't valid because A is abstract and you can't call new on any abstract class. If you could instantiate it, it would be an instance of A, but you can't.
The first statement is valid because it creates an anonymous class that extends A. This anonymous class isn't abstract (assuming A doesn't define any abstract methods), and so it can be instantiated. It's an instance of A because all subclasses are instances of their parent classes, abstract or not. It's basically a shortcut for saying:
public class AnonymousNameIDontCareAbout extends A
A a = new AnonymousNameIDontCareAbout();
answered Apr 5 at 3:36
Karl BielefeldtKarl Bielefeldt
121k32217415
add a comment |
The instanceof A has nothing to do with whether the statement is valid or not, so your question is simpler if you leave it off from both statements:
A a = new A() ;
A a = new A();
The second statement isn't valid because A is abstract and you can't call new on any abstract class. If you could instantiate it, it would be an instance of A, but you can't.
The first statement is valid because it creates an anonymous class that extends A. This anonymous class isn't abstract (assuming A doesn't define any abstract methods), and so it can be instantiated. It's an instance of A because all subclasses are instances of their parent classes, abstract or not. It's basically a shortcut for saying:
public class AnonymousNameIDontCareAbout extends A
A a = new AnonymousNameIDontCareAbout();
answered Apr 5 at 3:36
Karl BielefeldtKarl Bielefeldt
121k32217415
add a comment |
The instanceof A has nothing to do with whether the statement is valid or not, so your question is simpler if you leave it off from both statements:
A a = new A() ;
A a = new A();
The second statement isn't valid because A is abstract and you can't call new on any abstract class. If you could instantiate it, it would be an instance of A, but you can't.
The first statement is valid because it creates an anonymous class that extends A. This anonymous class isn't abstract (assuming A doesn't define any abstract methods), and so it can be instantiated. It's an instance of A because all subclasses are instances of their parent classes, abstract or not. It's basically a shortcut for saying:
public class AnonymousNameIDontCareAbout extends A
A a = new AnonymousNameIDontCareAbout();
answered Apr 5 at 3:36
Karl BielefeldtKarl Bielefeldt
121k32217415
The instanceof A has nothing to do with whether the statement is valid or not, so your question is simpler if you leave it off from both statements:
A a = new A() ;
A a = new A();
The second statement isn't valid because A is abstract and you can't call new on any abstract class. If you could instantiate it, it would be an instance of A, but you can't.
The first statement is valid because it creates an anonymous class that extends A. This anonymous class isn't abstract (assuming A doesn't define any abstract methods), and so it can be instantiated. It's an instance of A because all subclasses are instances of their parent classes, abstract or not. It's basically a shortcut for saying:
public class AnonymousNameIDontCareAbout extends A
A a = new AnonymousNameIDontCareAbout();
answered Apr 5 at 3:36
Karl BielefeldtKarl Bielefeldt
121k32217415
answered Apr 5 at 3:36
Karl BielefeldtKarl Bielefeldt
121k32217415
answered Apr 5 at 3:36
Karl BielefeldtKarl Bielefeldt
121k32217415
answered Apr 5 at 3:36
Karl BielefeldtKarl Bielefeldt
121k32217415
121k32217415
add a comment |
add a comment |
