but I'm not adding integers into an array...I'm adding OBJECTS of type Friend into an array of OBJECTS.... I have 3 client classes to write that I can't even begin until I get this right....and I have this wild feeling that I probably won't finish because...well, I haven't been taught any of this stuff and the book we have sucks. I've ... |
hi, Constructors do not create the instance of any class.They are used to initialize the instance variables of the class.In other words ctor are a part while the class is being instantiated.....In case of an abstract class ,the subclass which extend this parent class will be extending the methods and variables in the parent class..so when the child class is instantiated ... |
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By getStatus method your book or professor probably mean that setter methods should return success(true) or failure(false) as thier return values. This is a very common way to make sure things work the way they are supposed to rather then just assume that a method succeds. So I would look at your methods in student, setName() and setCreditHours() and see how ... |
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what i feel is that when we have to give a structure or ordering of things in the use of code like for e.g. suppose if we are writing a code for an organization which records various datas like salary, position, age etc in a hierarchy way then for this we can an abstract class employee with various variables like salary, ... |
I'm a beginner in Java and just learn about abstract method and class. However, i am wondering what is the point of using abstract method/class? Because when I delete the abstract method and change the class name to public class XXXX( changed from "abstract class XXXX), my program still runs well, nothing goes different. Is it because I haven't encountered any ... |
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Yes, it is possible. To see for yourself, create an abstract class with a method, and make that method final. Create a concrete class that extends your abstract class, and call the method you made final in your abstract class. I'd say that advantages and disadvantages would be the same as those you get from abstract classes and final methods - ... |
I'm working with an abstract class with 2 abstract methods and a few concrete methods. I derived a few classes from this abstract class and wrote out the abstract methods in each class. I wrote the main() method in the abstract class and want to call on both of the 2 methods from each class that I derived. How do I ... |
Hi, I was wondering if using abstract classes, which sub-class other non-abstract classes, is considered to be an acceptable form of coding, or whether it was a bad practice? I would've thought that abstract classes would normally reside higher up the inheritance hierarchy. I've come into a situation whereby it would make perfect sense to use an abstract class which still ... |
// code here } The Outputter class will keep a list of all logged-in users keeps a list of all the chats representing logged-in users, which it stores in a Vector.I am trying to use the getIDs() method to return an array of Strings comprising the IDs of all logged-in users, which is why im trying to use the getID() method ... |
public class test extends Frame implements KeyListener { Frame f; TextField t; test() { setBounds(50, 50, 500, 500); setLayout(null); f = new Frame(); t = new TextField(15); Panel p = new Panel(); p.setBounds(100, 150, 150, 50); p.add(t); add(p); setVisible(true); t.addKeyListener(new KeyAdapter() { public void keyReleased(KeyEvent e) { System.out.println("KeyReleased"); } } ); } public static void main(String as[]) { new test(); } ... |
is that a correct way to initailize the triangle constructor? Thanks No. Constructors are not inherited, you know. Your constructors as written don't work. In the Shape class, you assign the instance field, this.numSides to itself since you don't pass a numSides parameter. perhaps you meant something like this.numSides = sideLength.length; In the triangle class, you have not initilized any array ... |
I don't know what a HGV is, but whenever you have a Collection with multiple types, there's usually some bad design nearby. It sounds to me like the HGV and Vehicle don't need to be different classes, but an attribute of the same class. (I'm assuming HGV is a type of vehicle?) The Vehicle class could have a type, and the ... |
You know flounder, I appreciate this forum. I think its great that people who have knowledge are willing to share this knowledge with others. However what I do not appreciate is a condescending attitude from people with knowledge. I do not feel that I am asking out of line questions. If you care not to help, then please stay out of ... |
I just want to know that in how many ways can we use the non abstract methods of the class without extending the class(dont want to implement all abstract methods of the parent class).One way is that if the methods are static then we can use CLASSNAME.METHODNAME().Is their any other way of doing it |
The way I understand it....and I may be wrong because I am very new....is that by making the class abstract you will add abstract methods to it. Those abstract methods MUST be defined in in any subclass that inherits from the abstract class thereby making the abstract a template for subclasses. If your animal class is abstract then you would need ... |
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thankyou very much for your help. this question was posted by my husband who was trying to tell me how helpful this forum is and he is from a non-IT background. well i m impressed by this forum and will soon actively participate in it as soon as i finish my java certification. by the way i know the answer it ... |
Thanks fOR yOUR HELP GUYS I think ou both cleared my problem up. Thanks Again -Alex Edit: Just checking, but you cant directly create an instance of an abstract class can you? Even if there are some methods inside that are not abstract. Also is every method in java implicitly defined as virtual if not otherwise said Message was edited by: ... |
The compilation error occurs because Nowa, a non-abstract class, doesn't implement (i.e. provide code instructions) for the abstract method Costam.pisz(). Your solutions are either: * to make Nowa abstract (but then you can't create instances of Nowa); * to implement pisz() in Nowa; * to implement pisz() in Costam and make Costam non-abstract. But if you compiled Nowa with Costam non-abstract, ... |
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Problem: My Main method does nothing so my program does nothing when it runs. However, I cannot put the input statements in it (as they are run first) because they no longer recognise the variables that all my sub classes use too because Main is static. What can I do to improve my design so the program actually does something other ... |
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If there is no accessor method for 'age', then it is either mis-designed in the first place and you can't get around it without getting that class fixed, or it is not meant to be directly accessed and so is working as designed. Are you sure there isn't a public "getAge()" method or similar provided? |
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Ok my first question is how does the setAccessLevelID get called if this class is abstract and no object is created calling that constructor. The same way any method from an inherited class would be called. My second question is how are any of the methods in that class called, if they are not static, as no object of this class ... |
The reason you can't call my.m1() has nothing to do with abstract classes. It's because my is a reference to MyAbstract, and that only has method m(). Method m1() is declared on MyClass. The fact that the my reference variable happens to point to a MyClass object is irrelevant. It's declared as type MyAbstract, so you can only call MyAbstract's methods ... |
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If you want a great example of an abstract class (if I do say so myself!) take a look at [tjacobs.ui.menus.FileMenu in TUS|http://tus.svn.sourceforge.net/viewvc/tus/tjacobs/] This class I wrote actually extends a concrete (ie non-abstract class) and adds a ton of implementation surrounding the concept of a File menu. The one thing you can't code for is how to handle loading and saving, ... |
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ok lets say there was a subclass that inhereited another subclass...like a class Person, a class Student, and a class GraduateStudent; why would i want to make the class person abstract and have a abstract void display(); in it if i want to override that method in the subclasses lower on the inheritance tree? Wouldn't it do the same thing to ... |
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Hello, I have an interface with two methods. interface call{ void trial (int p); void show(); } And an abstract class that implements that interface with overriding only one method of the two. abstract class client implements call { public void trial(int num) { System.out.println(num);} } In the main method, I wanted to instantiate the implementing class in order to make ... |
public abstract Float deuda(); public abstract String saludo(); } And this is my child class: public class Vhs extends Formato{ private int dias; private int extra; public Vhs(int x){ dias=(x>0?x:0); extra=(dias>2?dias-2:0); } public Float deuda(){ return basico*penal*extra; } } So, when I tried to compile Vhs.java, it shows an error like: Vhs is not abstract and does not override abstract method ... |
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Get a hair cut! The Ubiquitous Newbie Tips * DON'T SHOUT!!! * Homework dumps will be flamed mercilessly. [Feelin' lucky, punk? Well, do ya'?|http://www.youtube.com/watch?v=1-0BVT4cqGY] * Have a quick scan through the [Forum FAQ's|http://wikis.sun.com/display/SunForums/Forums.sun.com+FAQ]. Ask a good question * Don't forget to actually ask a question. No, The subject line doesn't count. * Don't even talk to me until you've: ... |
My question is : Why we require an abstract class with no abstract methods and for this class we have to extend it and using instances of this subclass we will access its method. Rather, we can create a normal class and directly I can use its methods with the help its instance. |
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so i would say abstract as it says Abstract base class for implementing style factories. How can i tell? When do extend it i do still get the error of "no interface expected here". Cheers Edited by: nvidia1 on Nov 27, 2008 6:01 PM Edited by: nvidia1 on Nov 27, 2008 6:31 PM |
No please.. I just want to know if you have used it while programming. Like "an abstract class can be used to put all the common method names in it without having to write actual implementation code." I want to know its usage in programming, not just a definition. I guess you understand what I am looking for. |
Hi, You are correct in using the adding JPanel to the frame. Just because you haven't added any visible component you aren't seeing any effect. You would want to just add a button over the panel by modyfing your code little bit. Instead of writing frame.add(new JPanel()); You need to add the panel which overrides the paint methods: i.e. you need ... |
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I hate interviewers when they ask about specifics of some classes. It is as if anyone codes with only notepad and not look at the API's or google anything when they code. Perhaps interviewer is only gauging how familiar you are with the java language. So if I am asked I'd say: (some may be wrong of course) AbstractList Calendar bah! ... |
I've been put in a random group for some coursework, and the other people in my group aren't that keen on coding. I'm trying to make it easy for them to make the levels to the game we're making (the easiest bit :P). I don't really want them to have to ask me why they are getting NullPointerErrors and things. Sure, ... |
If you have a class full of callbacks--methods that some other code calls at certain times--and your class only cares about some of those calls. The calling class doesn't know about your particular implementation. It only knows that when you give it one of these types, it's supposed to call all these various methods at the various appropriate times. All the ... |
Ah, my two favourite posters at work. Maybe the OP tried it and was unsure of the result he was seeing, so he asked the friendly (ha!) people in the forum? It is great that the Java community has people like you, that are friendly and open and encourage people to learn the language and become part of this community... To ... |
Hi, I am reading a tutorial from internet well,I have read, that not can instead a abstract class, package exam.stuff;import cert.Beverage; class Tea extends Beverage { } We get an error something like Can't subclass final classes: class cert.Beverage class Tea extends Beverage{ 1 error but later I see that a class declared how default is instead class Zoo { public ... |
I was just wondering as I have seem to have forgotten. Say I have an Abstract class called Borrower. I then have 2 classes which extend this called maleBorrower and femaleBorrower. I create a maleBorrower and femaleBorrower Object. Should I be adding these to a Borrower ArrayList or an ArrayList of their type? Or does it depend on what I want ... |
Supposing you did that, how is the code using the interface to know which method(s) are available in this particular implementation? An interface is a contract, and the user is entitled to expect that contract to be fulfilled. If you have some classes which do things one way, and some the other, it would be better to put the two method ... |
Hm ok so if I make AbstractParameters a = new A() I can only call methods on 'a' specified in AbstractParameters. Unique methods in A are not visible for 'a'. But if I make A a = new A() I get everything in A and everything in AbstractParameters, so why would I ever want to do: AbstractParameters a = new A() ... |
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The concept of interface and abstract class overlaps sometime, but we can have the following thumb rule to use them for our specific need: 1) Interface: This should be use for code structuring. They standardize your application by providing a specific contract within and outside. If you think abstract class also provide structure, then reconsider as it limits the structure re-usability ... |
There is a JNI forum for JNI questions. I can't imagine what the issue might be - why would splitting the original object into two (superclass/subclass) cause such a problem? Crashes means that there is something wrong in your C/C++ code. Since GetByteArrayElements() is not JNI method (at least not in the code you posted) and since you say the problem ... |
A compile-time error only occurs when you declare an abstract method, but dont declare the class as abstract. If the class is abstract, but no method inside it is abstract, no compile-time error occurs (why should it occur?) but why should anybody declare the class as abstract anyway in that case (what sense does it make?)? regards BB |
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class Car extends Vehicle { public int speed() { return 6; } } public class RaceCar extends Car { public int speed() { return 12; } } public static void main(String[] args) { RaceCar racer = new Test().new RaceCar(); Car car = new Test().new RaceCar(); Vehicle vehicle = new Test().new RaceCar(); System.out.println(racer.speed() + ", " + car.speed() + ", " + ... |
ummmmm ok well i was planning on putting public Server toString { return - some way of returning the object (dunno yet) } but where would i need an .equals method inside the getServers? like public Server[] getServers(Server [] AbstractServer) { if(..... .equals("server requested") } is that what you mean or am i totally not getting you |
Ok, i think i understand better about abstract classes now. Just to make sure, Abstract classes and methods are implimented by their subclasses. This is the part i need clarifying. The subclasses can be instantiated by concrete classes which do not extend from them? e.g. So i have an abstract class called Person which has a constructor which creates a Person ... |
I didn't read all that code, but why are you trying to instantiate Person if it's abstract? Or, conversely, why did you make Person abstract if you're going to instantiate it? You make a class abstract when you want to define a type and provide some common or default behavior, but when there's some of that type's behavior that needs to ... |
In java method binding is always done at runtime unless the method is final. So, at run time jvm will find the it the derived class object ( since there cannot be base class obj because its abstract) and the base class method implementation will be called overriding the base class implementation |
I have written and tested an abstract-class inside a project. Now i moved the abstract class from my project to utility.jar Ten I added this utility.jar to my classpath. Using eclipse as my application devtool, i can see that the class is availabe in the jar (so far so good). But, when i add the import-statement to use the class in ... |
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You could write a Strategy pattern object where you would lay out the calls to interfaces but let them fill in the implementations as needed. You spell out what has to be done, but leave out how it's done. You don't have an abstract class that way. It's concrete, but it uses interfaces to spell out the sequence. % |
To save you from the wrath of the Java experts on this forum, allow me as a relatively new Java user to advise you: do NOT post homework problems here; you're just going to get told to go google the answer. Which would be a good move on your part. Especially since I found the answer to your questions by googling ... |
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I was asking from school (The school computer does not have JDK installed on it) Anyway, now that i am home: An abstract class can extend a non-abstract class An abstract class can implement an interface. The abstract class can "Pass the buck" and does not have to override the interface method. |
Hi guys, Just wondering if anyone can help me on this one. Basicaly I just need to know if it does make sence to have a composition association between abstract classes, as: AConnection, SomeConnection AChannel, SomeChannel Basically a connection cannot live outside the context of the AChannel. But should the composition relatioship be between the abstract classes or the concrete classes??? ... |
If i have Class A and Class B. They both inherit from the abstract class C. Now my question is, is Class C similiar to other non-instantiated classes and that any value set in this class can be accessed by any instantiated Class A or Class B objects. I dont want this to happen. I want them to share any data ... |
hi all i have an abstract class and i want to extend it such that it becomes a singleton. However i wish i can also gain the benefits of abstraction so that i can reference the abstract class whatever the concrete class that extends it so how can i write the "getInstance()" method in both the abstract and concrete classes knowing ... |
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From the names you've chosen, I'm going to guess that a more reasonable design and naming might have an interface called Analysis, with implementing classes named, say, BookAnalysis, CharacterAnalysis, SettingAnalysis, and ActionAnalysis. BookAnalysis would contain collections of the other analyses, and the word "Book" in the title would suggest that it's an analysis of the whole book, as opposed to elements ... |
Using your original code: By making Specific a subclass of Common, you can access C1 two ways: SpecificConstants.C1 or CommonConstants.C1 since C1 is inherited by Specific. If you use the first way, then there's no reason to have a separate superclass. If you use the second way, then there's no reason for Specific to be a subclass of Common. Either way, ... |
java.awt.Graphics is a GREAT example of an abstract class. It gives you an API (abstract public interface) to make method calls against, so that you can just fire and forget about the actual implementation. Then, on each platform which supports java, you can implement Graphics to work on that platform. The actual instances of Graphics are built into the JRE, but ... |
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I am using a GBPanel, running on a GBFrame. Because of the MouseListener I am using, the GBPanel has to be abstract. When I try to run the GBFrame, however, the abstract class gives me an error. This is what the GBFrame, or the program that runs the other, looks like : import BreezySwing.*; import java.awt.*; public class connect4game extends GBFrame ... |
I want to know that how we are able to use objects of abstract classes such as Calendar, even when an abstract class canot be instantiated. I is written about Calendar.getInstance() that it returns an object of the Calendar class. It returns an instance of a concrete subclass of Calendar. But every instance of a subclass is also an instance of ... |
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Yes, the entire purpose of abstract classes is to provide a (partial) implementation of functionality for subclasses to use. Without implementation, an abstract class is equal to an interface (except for the fact that you can extend only one (abstract) class, but implement multiple interfaces). For example, the AbstractCollection class (in java.util) provides an implementation for many of the methods defined ... |
Hello, I am writing some code that I'd like to be as generic as possible. I created an abstract class called Chromozome. This abstract class has a protected abstract method called initialize(). I also created an abstract class called Algorithm which contains a protected ArrayList. I would like to create a non abstract method (called initializePopulation()) which would create instances of ... |
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I am little bit confuse regarding the benefits of the abstract classes. Can anybody helps me in this regard. I just want to know when and what situation we may decide that particular class needs an abstract method. Sorry if I sound weary of this question, but it is asked about 3-4 times a week. Rather than have us go through ... |
package somepackage; import different.AbstractParent; public class ChildAbstractTest extends AbstractParent { } Now this class gives a compilation error "This class must implement the inherited abstract method AbstractParent.doStuff(), but cannot override it since it is not visible from ChildAbstractTest. Either make the type abstract or make the inherited method visible." I am trying to run my code from RSA 7.0 According to ... |
Hello Java Community, In dynamic biniding consept, it binds the appropriate method at run time... can any one please give me the reason how it identifes that perticular method is nearst one.....( i know that it first check sub class and then goes to super class ....... i just want how it identifys this process)..... As per java soft new release ... |
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hello, In this link only information about what is abstruct class and diffrence between abscrtuct class and infterface. I want ans with brief explanation. Why we can not create object of abstract class. short answer: because the language specifications say so why do they say that, though?? because it is an abstract entity, it represents a conceptual, rather than concrete, object. ... |
Hi, I have doubt in abstract classes,please clarify my doubt.....my doubt is I have one abstract class,in that i have three methods... Now I have created one subclass for that abstract class.... I defined all those methods that are there in abstract class in the sub class......and I wrote some other methods in that sub class.... Now my question is ----->can ... |