EPTInterfaces are, quite literally, ways to standardize how to interface with your objects. Other classes can now be written without knowing anything about that object, except that it implements the needed Interface. Just as the user interface abstracts away the nasty details of your program, so does an Interface abstract away from the nasty details of your object.
The Big Programming Thread - Page 680
| Forum Index > General Forum |
Thread Rules 1. This is not a "do my homework for me" thread. If you have specific questions, ask, but don't post an assignment or homework problem and expect an exact solution. 2. No recruiting for your cockamamie projects (you won't replace facebook with 3 dudes you found on the internet and $20) 3. If you can't articulate why a language is bad, don't start slinging shit about it. Just remember that nothing is worse than making CSS IE6 compatible. 4. Use [code] tags to format code blocks. | ||
|
Acrofales
Spain18050 Posts
Interfaces are, quite literally, ways to standardize how to interface with your objects. Other classes can now be written without knowing anything about that object, except that it implements the needed Interface. Just as the user interface abstracts away the nasty details of your program, so does an Interface abstract away from the nasty details of your object. | ||
|
spinesheath
Germany8679 Posts
On November 22 2015 09:39 Acrofales wrote: Better to see interfaces as Java's slightly quirky way of dealing with multiple inheritance. It's not wrong what you're saying, but it's a rather dry statement of the definition that doesn't show an understanding of what what the purpose of Interfaces are in Java and what their intended use is. Interfaces are, quite literally, ways to standardize how to interface with your objects. Other classes can now be written without knowing anything about that object, except that it implements the needed Interface. Just as the user interface abstracts away the nasty details of your program, so does an Interface abstract away from the nasty details of your object. It's not multiple inheritance and I certainly wouldn't mention multiple inheritance in the definition of an interface. Interfaces can hardly be called "quirky". On the contrary, I would go as far as calling pure virtual classes in C++ a quirky way of implementing interfaces. Especially if you need to use multiple inheritance to implement multiple interfaces and your compiler doesn't apply the empty base class optimization, which still was common practice last time I read about it. I find it a good thing that explicit interfaces create a clear separation of implementation and usage. | ||
|
Ropid
Germany3557 Posts
 EDIT: Turns out, it's a lot more complicated and not just an index in a table: There is no simple prefixing scheme in which an interface's methods are displayed at fixed offsets within every class that implements that interface. Instead, in the general (non-monomorphic) case, an assembly-coded stub routine must fetch a list of implemented interfaces from the receiver's InstanceKlass, and walk that list seeking the current target interface. Once that interface is found (within the receiver's InstanceKlass), things get a little easier, because the interface's methods are arranged in an itable, or "interface method table", a display of methods whose slot structure is the same for every class that implements the interface in question. Therefore, once the interface is found within the receiver's InstanceKlass, an associated offset directs the assembly stub to an itable embedded in the InstanceKlass (just after the vtable, as one might expect). At that point, invocation proceeds as with virtual method calls. I'd guess that's not done every time. Perhaps the JIT optimizes that away and that whole bunch of stuff happens just once for every spot in the program where a call is? | ||
|
Deleted User 3420
24492 Posts
So when my comp sci class asks me to write a 2 dimensional string array, is that really just a 3 dimensional character array? (like, I won't write it that way - but that's what it really is?) edit: Okay, I am very confused I am writing in eclipse and I write: String[][] stringArray = new String[2][2]; stringArray[0][0] = "hello"; stringArray[0][1] = "hallo"; stringArray[1][0] = "hyllo"; stringArray[1][1] = "hullo"; but it refuses to accept this. It is making me put stringArray[0][0] = "hello"; stringArray[0][1] = "hallo"; stringArray[1][0] = "hyllo"; stringArray[1][1] = "hullo"; inside braces. So it is making me write String[][] stringArray = new String[2][2]; { stringArray[0][0] = "hello"; stringArray[0][1] = "hallo"; stringArray[1][0] = "hyllo"; stringArray[1][1] = "hullo"; } Why am I having to put that in braces??? | ||
|
Thaniri
1264 Posts
At least thats how I understood it, im also a comp sci student and thats just how it's done. | ||
|
Faust852
Luxembourg4004 Posts
On November 23 2015 00:23 travis wrote: Okay, so a string is already an array, yeah? So when my comp sci class asks me to write a 2 dimensional string array, is that really just a 3 dimensional character array? (like, I won't write it that way - but that's what it really is?) edit: Okay, I am very confused I am writing in eclipse and I write: String[][] stringArray = new String[2][2]; stringArray[0][0] = "hello"; stringArray[0][1] = "hallo"; stringArray[1][0] = "hyllo"; stringArray[1][1] = "hullo"; but it refuses to accept this. It is making me put stringArray[0][0] = "hello"; stringArray[0][1] = "hallo"; stringArray[1][0] = "hyllo"; stringArray[1][1] = "hullo"; inside braces. So it is making me write String[][] stringArray = new String[2][2]; { stringArray[0][0] = "hello"; stringArray[0][1] = "hallo"; stringArray[1][0] = "hyllo"; stringArray[1][1] = "hullo"; } Why am I having to put that in braces??? public static void main(String[] args) {it does work in my Eclipse. result : hello My guess would be it's making an constructor for this array to complete it because it can't do it directly if it's declared as an instance variable, not sure though, I'm not a java pro. | ||
|
Deleted User 3420
24492 Posts
| ||
|
Blitzkrieg0
United States13132 Posts
String[][] stringArray = new String[2][2] {You should be able to initialize it like this. Not sure where all the extra semicolons are coming from. It'd be equivalent to declaring an array like int[] numbers = new int[10] {1,2,3,4,5,6,7,8,9,0}; | ||
|
Manit0u
Poland17341 Posts
On November 22 2015 09:39 Acrofales wrote: Better to see interfaces as Java's slightly quirky way of dealing with multiple inheritance. It's not wrong what you're saying, but it's a rather dry statement of the definition that doesn't show an understanding of what what the purpose of Interfaces are in Java and what their intended use is. Interfaces are, quite literally, ways to standardize how to interface with your objects. Other classes can now be written without knowing anything about that object, except that it implements the needed Interface. Just as the user interface abstracts away the nasty details of your program, so does an Interface abstract away from the nasty details of your object. I'm not sure how it works in Java but in PHP if a class implements certain interface it also becomes an instance of said interface. This is awesome because it lets you create truly modular code by typehinting interface classes instead of what's implementing them, thus allowing you to freely switch between different classes implementing the same interface as parameters. Also, to combat multiple inheritance, I highly recommend this brief article: http://ocramius.github.io/blog/when-to-declare-classes-final/ I know for a fact that using final and abstract keywords, as well as interfaces has improved the quality of my code greatly. | ||
|
Blisse
Canada3710 Posts
On November 23 2015 00:23 travis wrote: Okay, so a string is already an array, yeah? So when my comp sci class asks me to write a 2 dimensional string array, is that really just a 3 dimensional character array? (like, I won't write it that way - but that's what it really is?) Why am I having to put that in braces??? On November 23 2015 01:45 travis wrote: ah ok, it looks like it's not necessary in main but outside of main it is What? No you shoudln't have to put them in braces. The code should work regardless of being in main or not. You're not posting real code because those two should compile fine. If that is real code then something else is wrong. All you've done in the second piece of code is put those assignments in another scope, which does nothing. There's a semi-colon before your braces so you're not doing array initialization, and that'd be the incorrect syntax for it too. Don't think of 2D arrays as a grid, or 3D arrays as a cube. A 2D array is simply a list of lists. A 3D array is simply a list of lists of lists. It's silly to relate them to other ideas when they're literally just a list of other lists. edit: "regardless of being in main or not" ... obviously a gross oversight on my part because my assumption was that if code wasn't in main it was in another function being called by main, which isn't the case here.... totally overlooked the possibility the code was being placed outside of functions... oops | ||
|
Deleted User 3420
24492 Posts
http://imgur.com/TYyZO3P this is the original code http://imgur.com/E4pZGBP the error on both says "Syntax error on token ";", { expected after this token | ||
|
Blisse
Canada3710 Posts
All of your stringArray stuff is being declared as member variables, which is invalid. You have a class ewt that has a member variable stringArray and function returnedArray. Those are legal declarations for classes. But stringArray[0][1] = "hello" is an assignment, and that isn't a legal declaration (or a declaration at all). Assignments are only valid inside functions (like main). Someone else can explain this better because I'm at a loss at explaining this better (not in position to write/post code). | ||
|
Soan
New Zealand194 Posts
This is fine and good, you're declaring a new String[][] as part of the class ewt. If you want to assign values to this array like you are doing, you will need to do it inside a function that is part of that class. Either in the constructor or some other function.
Or you can do it like Blitzkrieg0 said a couple posts above, and initialise it inside curly braces when you declare it. | ||
|
Housemd
United States1407 Posts
So, right now, I've started working on it by taking the response and putting it into a string and taking the keywords and putting them into a string. This is c++ and here is the current code that checks the words in each string. It compiles but I'm not entirely sure if it works 100% and since I don't really have anything to test it on, could someone who knows more than me check if it will work as intended? bool checkStrings (string str1, string str2){ vector <string> words1, words2; string temp; stringstream stringstream1(str1); while (stringstream1>>temp){ words1.push_back(temp); } stringstream stringstream2(str2); while (stringstream2>>temp){ words2.push_back(temp); | ||
|
Manit0u
Poland17341 Posts
| ||
|
Zocat
Germany2229 Posts
On November 23 2015 04:34 Housemd wrote: It compiles but I'm not entirely sure if it works 100% and since I don't really have anything to test it on, could someone who knows more than me check if it will work as intended? Then you have to test it yourself. Make up a list of keywords and an answer sentence and see what happens. What kind of scenarios can happen? The sentence contains all keywords, the sentence contains some keywords, the sentence contains no keywords. (In practice you might also want to check what happens when your input is empty / wrong). | ||
|
Blitzkrieg0
United States13132 Posts
On November 23 2015 03:04 Blisse wrote: The problem isn't your code, it's where you're putting them. Damn this will be hard to explain over the Internet... All of your stringArray stuff is being declared as member variables, which is invalid. You have a class ewt that has a member variable stringArray and function returnedArray. Those are legal declarations for classes. But stringArray[0][1] = "hello" is an assignment, and that isn't a legal declaration (or a declaration at all). Assignments are only valid inside Someone else can explain this better because I'm at a loss at explaining this better (not in position to write/post code). Adding onto this... Where you placed the code it will never be run. Since it isn't in a method the code will never be executed. You either need to initialize the values when the array is declared (see my previous post). If the values will always be the same then this is how it should be done. Alternately you can make a constructor which will add values to the array when the object is created: public class ewt {If you actually want to add any amount of values then utilizing an Arraylist instead of an array will be helpful so you don't have to worry about size. | ||
|
Cyx.
Canada806 Posts
On November 23 2015 03:04 Blisse wrote: The problem isn't your code, it's where you're putting them. Damn this will be hard to explain over the Internet... All of your stringArray stuff is being declared as member variables, which is invalid. You have a class ewt that has a member variable stringArray and function returnedArray. Those are legal declarations for classes. But stringArray[0][1] = "hello" is an assignment, and that isn't a legal declaration (or a declaration at all). Assignments are only valid inside functions (like main). Someone else can explain this better because I'm at a loss at explaining this better (not in position to write/post code). http://stackoverflow.com/questions/2420389/static-initialization-blocks http://stackoverflow.com/questions/3987428/what-is-an-initialization-block Inside a class but outside any method is where you *declare* variables - you can't modify them there. That's what you're trying to do when you say 'stringArray[0][1] = "hello"'. If you put a block of code within a class but outside a method, ie. surrounded in braces like you did, that's an *initialization block*, which gets run before the class is constructed. You can also prefix the block with 'static' to make it a static initalization block, which gets run once, before *any* instance is constructed. As an aside, you can also initialize it when you declare it like so:
| ||
|
Blisse
Canada3710 Posts
http://stackoverflow.com/questions/3987428/what-is-an-initialization-block | ||
|
WarSame
Canada1950 Posts
| ||
| ||
