JavaDocs Says Interfaces Cannot Have Fields?
May 20, 2014This is the link [URL] and it says One significant difference between classes and interfaces is that classes can have fields whereas interfaces cannot.How can this be possible?
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How To Add Javadocs For BlueJ
Oct 7, 2014I am new to BlueJ. I have to add Javadocs every time I finish the program, but I see a folder named "doc" .
What's that folder ? Is it Javadocs?
I see :ToolsProject Documentation => regenerate??
JSP :: How To Differ Between Fields That Not Exist To Fields That Are Null
Dec 7, 2014how to differ between fields that are not exists to fields that are null? because in my api when someone wants to delete a field he sends null instead of a value. and if he doesnt want to effect this feild he doesnt send it.
{
"a" : {"1","2"},
"b" : "hello"
}
{
"a" : null,
"b" : "hello"
}
{
"b" : "hello"
}
Can Interfaces Be Instantiated
Feb 14, 2014Interfaces are 100 % abstract classes.They cannot be instantiated.Their sole purpose is to be implemented.So why does the following code works just fine while it is attempting to instantiate an interface.
interface TestA { String toString(); }
public class Test {
public static void main(String[] args) {
System.out.println(new TestA() {
public String toString() { return "test"; }});
}
}
Using Constructors In Interfaces?
Sep 1, 2014Can i use constructors in an interface?
interface AI {
public abstract AI();
public abstract void hello();
}
Output:
I got the error as the method AI() should have return type.
Interfaces In Java API
May 14, 2014I understand that interface methods are abstract. I don't understand what the methods in the API do if the method bodies are empty. For example, say there are two interfaces, both with one method with no parameters. What would make these two interfaces different from each other. In the API, the AudioClip interface has the methods play(), stop(), and loop(). If abstract methods have no method bodies, and these methods take no parameters, what makes them different from each other.
View Replies View RelatedWhy Interfaces Are Needed In Java
Dec 5, 2014 why interfaces are needed in Java,Now you saw what a class must do to avail itself of the s... - justpaste.it (if I paste the quote here, I get the "Page not found" error after posting -.^)
the first fragment reads that the compiler must be sure that a method exits at a compile time, whereas the second fragment denies it - if a[i] doesn't have the specified compareTo method, a JVM simply throws an exception.
Hibernate Core Interfaces
Jan 8, 2015In Interview many times Interviewer ask a simple question "Hibernate core Interfaces ?".The five core interfaces exposed by Hibernate. But he not satisfy, Why?...
View Replies View RelatedAbstract Classes And Interfaces
Mar 29, 2014 I did research again....
interface:
methods - abstract, default, static ONLY(abstract methods have no body, while static and defaults do, right?)
fields - public, static, final ONLY
abstract class: a normal class, but has at least one abstract method
methods - all
i.e., static, non-static, abstract (can it have a default method?)
fields - all
i.e., public, protected, private / final, non-final / static, non-static
Nesting Interfaces Inside Classes
Jun 20, 2014When are we allowed to nest interfaces inside a class? Would this be possible? Why or Why not?
View Replies View RelatedStatic Methods In Java Interfaces?
Jun 16, 2010Why can't we have static methods in an interface?
View Replies View RelatedClasses Of Object - Implement Two Out Of Three Interfaces
May 8, 2014I have three classes of object, most of which must implement two out of three interfaces. The interfaces look like this:
public interface Source {
public void startSending();
} public interface Sender {
public void setReceiver();
[Code] .....
That works fine, but I am wondering if pairing the interfaces into subinterfaces is a defensible methodology. For example, all classes that act like Producer must implement both the Source and Sender interfaces. And all classes that act like Relayer must implement the Sender and BlackHole interfaces. I could define two subinterfaces like this:
public interface Factory extends Source, Sender {
}
public interface Modifier extends BlackHole, Sender {
}
I could then define my classes like this:
public class Producer implements Factory {
}
public class Relayer implements Modifier {
}
public class Consumer implements BlackHole {
}
Within the class definitions, it makes no difference, as I will have to implement the same methods either way. But it seems more self-documentary to create the subinterfaces from their parent interfaces and name them in ways that reflect what the classes that implement them must actually do.
How To Simplify Classes By Using Interfaces And / Or Inheritance
Apr 6, 2014I am trying to figure out how I can most easily make it easier to make new types of units in my game. I have buildings and ships, and would like to know how I could make it easy to add new units. I have been recently told about interfaces, and have worked with inheritance a little bit.
What I would like to able to do is have it so that all of the variables and methods common to all ships could be stored in a superclass or interface, and same with the buildings. I would also like to be able to assign behaviours to the buildings and ships, maybe as interfaces, which could contain all of the methods and variables required for the functions of that ship or building.
For example, creating a new type of building that can shoot, build ships, and can regenerate nearby ships. So it would possible inherit all of the variables and methods common to all buildings, such as health, image, x, y, getX(), getY() etc. But it would then also gain the variables and methods essential for its functionality, such as shootRange, shoot(), regenRate, etc.
How could this best be achieved?
Why Static Classes Are Allowed In Interfaces
Oct 25, 2014I am reading about interface and i see that classes are allowed inside interfaces which are implicitly static. Here is sample of code i created and i am able to access the static method and fields as well. Here is the code snippet.
public class TestInnerClass {
public static void main(String[] args){
Test.NestedClass.printMe();
}
}
interface Test{
static class NestedClass{
static int x = 100 ;
public static void printMe(){
System.out.println(x);
}
}
}
My question is what is the use of such static classes inside interface? If i don't have access to Foo, i can't ever invoke NestedClass. Whats the design usage?
Interfaces Using Generic Type Constructions
Jan 16, 2014I want to make some library interfaces for a graph.Using these interfaces:
Graph<V,E>
Edge<E>
Vertex<V>
how can i constraint users of this library to use the same type <E> in the graph and edge interface and type <V> in the graph and vertex interface??
How Multiple Inheritance Is Possible In Java With Interfaces
Apr 11, 2014This is my assignment.
Identify how multiple inheritance is possible in Java with interfaces.
Write a java programme with appropriate classes to demonstrate the above.
Hint: both inheritance and interface concepts are necessary.
For the project name in netbeans, use your id and the name "assignment" separated by underscore,
E.g. 9876543_assignment
Implement Multiple Inheritance In Java Using Interfaces?
Jan 12, 2014how can i implement multiple inheritance in java using interfaces. if interfaces have some methods having same name then how to distinguish that ?
View Replies View RelatedWhy Super Classes Always Declared As Interfaces And Not Abstract Class
Dec 1, 2014While reading the design patter book, i got one doubt ,There is a List an interface having sub classes ArrayList, LinkedList etc.,
Q1) My question is Why they declared the List as interface rather than Abstract class?
Q2) i read some site -
List l = new ArrayList(); Why it is GOOD line?
ArrayList l = new ArrayList() ; Why it is BAD line?
Answer required with detailed information for Q1 and Q2.
Casting And Interfaces - Comparing Object Of Unknown Types
Oct 15, 2014import java.util.*;
public class CommonElements
{
private int comparisons; // number of comparisons made
private Comparable[] arrayToSearch; // current array being traversed
private Comparable[] commonElements = new Comparable[10];
private int arrayPosition = 0; //keeps track of what index to add an element to common at
[Code] ...
I have trying to get this down to the bar minimum. I am trying to cast the desired object array to a array of comparable. This is all required by the assignment.
I am getting a runtime error that I can not perform the desired cast. What do I need to provide the compiler in order to allow for this casting. I can not change the signature of the method however nothing about the class has been specified do I need to implement comparable? Also I don not now what the client is passing so how would I write a generic compareTo method to compare object of unknown types.
Ambiguity When Implementing Multiple Interfaces With Same Method / Variable Names?
Oct 14, 2014imagine you are implementing 2 interfaces having identical method signatures:
interface A {
void doStuff();
}
interface B {
void doStuff();
[Code] ....
How can I implement both methods?
Or another example with member variables:
interface A {
public static final int i = 3;
}
interface B {
public static final int i = 33;
[Code] ....
How can I go about making clear which 'i' is meant?
Fields Won't Hold Value Given Through Input?
Oct 18, 2014At the end of my main method, I want it to print out the input given that should have been stored in my sandwich class fields, but it didn't.
import java.util.*;
import java.lang.*;
public class SandwichBuilder {
public static void main(String[] args) {
Scanner inputDevice = new Scanner(System.in);
[Code] .....
Order Of Static Fields
Nov 20, 2014 I am unsure of something. In the following class, which is read first; the static field or the main method?
class Test{
static int a = 3;
public static void main(String args []) {
//some code}
}
I put some code in Eclipse and have tried to look at the hierarchy. It would point to all static fields being initialized in order from top to bottom, including the main method.I had thought that the main method was always the first thing in a public class to be initialized, regardless of where in the code it resides. Am I reading the Eclipse hierarchy wrong? I find Eclipse very difficult, especially since I typically code in Textmate. I just want to see how my code is operated upon,
Static Fields And Inheritance
Apr 17, 2014If I define a class which contains a few static fields, and then have a few classes who inherit this class, then all these classes would have the static field as well. Now my question is the following: would all those sub classes (and the base class itself) share the same object, or would each class have one object for all it's instances?
View Replies View RelatedSending Values For GUI Fields
Jul 9, 2014I have a simple class, called InputManager, which has methods that communicate with another class DatabaseManager which has access to Database which is actually object that contains information about actual database.
My JFrame has Navigation class (extends JPanel). There I put all needed JButtons, JLists and so on.. This class has instance of InputManager and when user interacts with GUI components inside of it, Navigation calls InputManager methods, it then analyses the call and calls needed methods on DeviceManager, which then sends queries to Database and etc.
The problem is, that at the beginning (when user runs a program), I want to get information (which is actually values for my GUI components ) from Database. It could, for example, create another DatabaseManager and connect to the Database to get information, but it is okay to have two objects?
I was also thinking about sending same DatabaseManager object through InputManager to Navigation, but it seems strange for me to have two objects, which can interact with each other in both directions(Class A has instance of Class B, and Class B has instance of Class A). Is there anything bad this can do?
Also what I noticed that it seems odd that GUI class would have to get information from database. (Logic in GUI class).
Sorting Objects By A Number Of Fields
Mar 17, 2014I am trying to find a concise way to write the sort methods for my class. I am supposed to make a program that can sort objects by a number of fields: year, rank, artist and title.
I used an idea from this thread : java - Sorting a collection of objects - Stack Overflow
And I am trying to use the custom comparator for my sort methods. However for some reason, the sortingBy variable fails to recognize any of the enum types.
Whenever I try to set the sortingBy variable equal to one of them, for example:
Java Code:
private Order sortingBy = Year; mh_sh_highlight_all('java');
I get a "Year cannot be resolved to a variable" error.
What I want to be able to do is make it so every time a specific method is called, say, for example sortTitle(), sortingBy will change to Title, then the SongComparator will sort using the case Title.
Is it possible to do this? I can't figure out how to modify SongComparator's object variables that way.
Java Code:
import java.util.Comparator;
public class SongComparator implements Comparator<Song> {
public enum Order {Year, Rank, Artist, Title}
public Order sortingBy;
[Code] .....
Get Values From Database And Set Them In Text Fields?
Apr 24, 2014I have a button in which I need to do the following:
After I click it It reads the values given in a jtextfield1 and in the other jtextfields I need it to settext in them from the database I mean if I have for example id=1 when I click the button it goes to the database and find the id 1 then write the infos in the other textfields