I need to make a model of cellphone with:
3 types of dates with appropriate name and date.
Set and get methods: at least 6.
At least 1 method defining typical behavior of the object.
Can you please tell me how to begin doing that. It's one of my first projects and I don't really know how to begin with this.
Any tips would be helpful I just dont know what is asked of me exactly and how to go about doing it.
Let's do it. You need to create a Java Class to model a cellphone.
1.- A `class` is a definition of a kind of object, which models an element.
So you're going to make a class to represent this cellphone.
2.- Variables store data.
You're asked to store 3 different kind of data about the cellphone. Just pick 3, what about the brand i.e.? You can use it and two more.
You will have to declare one variable inside your class to store each one of these values. About the apropriate name, it means to don't call that vars "var1" nor like this, but something with semantic meaning like "cell_brand", which gives you the meaning of it when you read the code.
3.- Properties: get and set
Classes let us encapsulate data and methods inside it. Then, you need to make this data accesible from the outside. This is achieved by get/set methods. The first one let you obtain the data from the property you define, and the second one to change it.
4.- Methods
Explained simple, a method is "a piece of code which you can ask to execute when you want, without needing to write it again". It operates over the object where it's contained.
Then, you need to write a method to simulate one behavior of the cell phone: a call, a message, etc.
5.- Do it
You will need to look for how to make these things on java. There're billions of tutorials on Internet, I'll leave here the first I found. Good luck
Java Classes
Related
The question I have is so weird that I couldn't even come up with a better title at the moment. Anyhow, I am looking for a way to name 2 classes but cannot figure out what would be the best way forward. I do understand this is an opinion based question but I'm stuck with this... so I would appreciate any opinion on this
Project: A
-> Class name: Call (This class will represent the call from one telephone to another) Other classes may/may not subclass this particular class and if so the name of these subclasses would probably relate somehow to the parent class (CallState, CallEndPoint, CallSomething). This Class will not know about the existence of the database, one could say this class will be part of the general telephony driver.
Project: B
-> Class name: Call? (This will represent the actual table in a database. The table will have some information about the call like call id, time it entered the system etc, but also other information that may/may not relate to the call). This class will serve essentially as a RowMapper.
Now, these 2 projects most likely will be combined down the line, and If I name the classes the same I would then end up with 2 same name classes in a single project serving 2 different purposes. Now if I was the only person to build this application I could probably digest this, but if multiple people start work on the application it will become confusing to others, especially if more classes will follow the same pattern.
I'm not entire sure what the question here is. Do you want to know if it's possible to give 2 classes the same name, or just whether it's a bad idea?
A convention that is often used for classes that are meant to model database entities, is to postfix the classname with Entity. So you could name the first class Call and the second CallEntity. This removes some ambiguity about the classes purposes. Most professional developers will also immediately make the assumption that the Entity class is supposed to represent something that is persisted.
However if you really insist on giving both classes the same name. That's perfectly possible, if you put them in separate packages. The package you put them in can also provide more clarity about the intent of the class. The first could be domain.model.Call, while the second could be domain.entity.Call
Hope this is somewhat helpful :)
Now, these 2 projects most likely will be combined down the line, and
If I name the classes the same I would then end up with 2 same name
classes in a single project serving 2 different purposes.
When inside a same application two classes with distinct responsibilities/data need to have the same simple name (that is without the package), you should indeed consider it as something to think of and very probably fix.
Of course you could define these classes in distinct packages but does it really solve your issue ? I don't think. It will make things less clear as client code could use the bad one and at each time developers manipulate/read Call in the code they have to wonder "which Call" they are currently copping with.
Today you have two distinct Call. With such permissive naming conventions, why not a new one in the future ?
Really, not a good idea.
The source of the problem is the way which you design your application.
You split the model in two pats : the agnostic persistence part in a class and the data persistence part in another class. It is a choice (that personally I avoid) but if you make this choice you have to go until the end : distinct clearly each class with a different name. This choice has to be visible and not hidden in a package name only.
For example :
Call (domain) and CallEntity (persistence) or in the reverse way CallDTO(domain) and Call(persistence)
I'm trying to write a REST interface to manage one of the resources in my application. Following best practice only I want to only use nouns as resource names.
I need the ability update the resource (a PUT operation) in one of several different ways. I imagine my user would call something like:
/resource/{name}?Operation=DO&time=1&Unit=HOUR
/resource/{name}?Operation=REDO&time=1&Unit=HOUR
/resource/{name}?Operation=UNDO
(I'll probably have more then 3 operations, but this is enough to show what's going on). One of the important things that the operations have different arguments. Logically time and Unit do not make sense to the UNDO operation.
In my Java back end I'd like to implement this with two different methods each of which will have it's own #RequestMapping annotation. The differentiator will be the value of the Operation parameter. I can't find any documentation that tells me how to do this
The alternative is to have a single method at the backend, but this is really ugly as I'll have to work out what combination of parameters is valid and throw my own 404 errors if they don't match!
If you absolutely need 2 controllers then do something like
/resource/do/{name}/{time}/{unit}
/resource/undo/{name}
Is there a way to make a collection of class files/objects and then have them used in an interactive main file? So let's say I want to make a program to store information interactively where different classes are designed to hold different information. Then I would have an interactive main file where I made instances of these classes which would collectively hold the information I want stored. And then any changes or anything I do in this interactive main file is then saved.
I understand that this might be a very odd inquiry and maybe some other program might be useful for this. If so, feel free to point me in the right direction.
Here are two solutions that are good for the purpose you mentioned in your comment.
The first one is called Serialization. This let's you save your java object to your hard drive, and retrieve it later.
The second, (and in this case, more preferable option in my opinion), is using a Database.
A database is a compliment to your program, that stores data. You can then use "Queries" to access this data, and update it. Almost every database software is compatible with java.
I would look into MySQL
The reason I think a database would be better for your purpose is that they are already highly optimized, and are designed to have multiple people accessing and writing to them at once. If you wanted just want one person to use this program at a time however, serialization might be easier to implement.
Absolutely! Your main class would use the standard input (perhaps Scanner input = new Scanner(System.in);) and output (System.out.println()). To interact with your other classes, most simply, just put them in the same folder (if you are interested take a look at Java packages). If you have a Dog class in the same folder as your main class, you can freely create Dog objects in your main class. I hope this helps!
As a side note, because you mentioned storing information with different classes, you might be interested in the Java Collections Framework.
I'm using an API providing access to a special server environment. This API has a wide range of Data objects you can retrieve from it. For Example APICar
Now I'd like to have "my own" data object (MyCar) containing all information of that data object but i'd like to either leave out some properties, augment it, or simply rename some of them.
This is because i need those data objects in a JSON driven client application. So when someone changes the API mentioned above and changes names of properties my client application will break immediatly.
My question is:
Is there a best practice or a design pattern to copy objects like this? Like when you have one Object and want to transfer it into another object of another class? I've seen something like that in eclipse called "AdapterFactory" and was wondering if it's wide used thing.
To make it more clear: I have ObjectA and i need ObjectB. ObjectA comes from the API and its class can change frequently. I need a method or an Object or a Class somewhere which is capable of turning an ObjectA into ObjectB.
I think you are looking for Design Pattern Adapter
It's really just wrapping an instance of class A in an instance of class B, to provide a different way of using it / different type.
"I think" because you mention copying issues, so it may not be as much a class/type thing as a persistence / transmission thing.
Depending on your situation you may also be interested in dynamic proxying, but that's a Java feature.
I am newbie to Java. I have some design questions.
Say I have a crawler application, that does the following:
1. Crawls a url and gets its content
2. Parses the contents
3. Displays the contents
How do you decide between implementing a function or a class?
-- Should the parser be a function of the crawler class, or should it be a class in itself, so it can be used by other applications as well?
-- If it should be a class, should it be protected or public class?
How do you decide between implementing a public or protected class?
-- If I had to create a class to generate stats from the parsed contents for eg, should that class be protected (so only the crawler class can access it) or should it be public?
Thanks
Ron
I think Andy's answer is very good. I have a few additions:
If you believe that a class will be extended in the future, you can set all your private methods (if any) to protected. In this way, any future extending classes can also access these.
I like the rule that a method shouldn't be longer than that you can see its opening and closing brackets ({ }) without scrolling. If a method is longer than that, try to split it up into several methods (private, protected or public by your preference). This makes code more readable, and could also save on lines of code.
So let's say a method is getting big and you split it up into several private methods. If these new methods are only used within the first "mother"-method, it makes sense to move all of that into a class of its own. In this way you will make the original class smaller and more readable. In addition, you will make the functionality of the new class easier to understand, as it is not mixed up with that of the original class.
The best guidance I've seen for these types of questions is the "SOLID Principles of OO Design."
http://butunclebob.com/ArticleS.UncleBob.PrinciplesOfOod
The most basic of these principles, and the one that sort of answers your first question is the "Single Responsibility Principle." This states that, "a class should have one, and only one, reason to change." In other words, your classes should each do exactly one thing. If you end up needing to change how that one thing works, you only have one class to change, and hopefully just one place to make the change within that class. In your case, you would probably want a class to retrieve the content from the URL, another class to parse it into some sort of in-memory data structure, another class to process the data (if needed), and yet another class (or classes) to display the content in whatever format you need. Obviously, you can get carried away with classes, but it's typically easier to test a lot of small, single-operation classes, as opposed to one or two large, all-encompassing classes.
The question on public vs. protected depends on how you plan to use this code. If your class could be used independently outside your library, you could think about making it public, but if it accomplishes some task which is specific or tied to your other classes, it could probably be protected. For example, a class to retrieve content from a URL is a good general-purpose class, so you could make it public, but a class that does some specific type of manipulation of data might not be useful outside your library, so it can be protected. Overall, it's not always black and white, but ultimately, it's usually not a huge deal either way.
I like to think of classes as "guys" who can do specific stuff "methods".
In your case, theres a guy who can fetch the content of an url if you tell him which url that is.
Then there is this another guy, that is really good at parsing content. I think he does that with a tool called rome, but i'm not sure. he keeps that private (hint ;) )
Then we have that third guy, who displays stuff. He's a bit retarded and only understands stuff that "another guy" produces, but hey thats fine.
Finally the project needs a boss guy, who gives orders to the other 3 guys and passes messages between them.
ps: I never really though about making classes protected or not. Usually they are simply public without any specific reason. As long as it don't hurt, why bother?