Variable In Interface Cannot Be Instance Scope?
May 5, 2014
I'm just wondering why variables in interface can't be instance scope?
interface Test{
int a;
}
And then
Test test = new TestImpl();
test.a=13;
Yes, it violates OO, but I don't see why this is not possible? Since interface is not an implementation, therefore it can;t have any instance scope variable. I can't find the correlation of interface being abstract and being able to hold instance scope variable. There's gotta be another reason. I'm just curious about any programmatic limitation, not deliberate design constraint. the example of programmatic limitation is like when Java forbids multiple inheritance since when different parents have the exact same method, then the child will have trouble determining which method to run at runtime.
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Jun 2, 2014
A distributed application consists of modules which run on different machines. How is this possible? Does it have any link with the public modifier?
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Sep 11, 2014
Viewing this example of pagination [URL] and other similar beans for pagination, why do they do these beans view scoped? These beans dont contain any properties for a form so they could be application scoped, right?
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Mar 7, 2015
I am currently trying to use Junit to test a whole bunch of stuff. I almost have full line coverage but I am getting hung up on testing an if statement that consists of whether or not an object is an instance of another class. This class happens to be an interface, and even the object is an interface. Weird I know but I just want to know how to get into that if statement. I realize testing interfaces might be a waste of time but I still really want to know how. Here is an example of what I am trying to test:
Java Code:
if(x instance of y){ //where x and y are both interface objects
doSomething();
} mh_sh_highlight_all('java');
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Apr 14, 2015
I have been researching the Iterator and making a class implement iterable. I have seen this example shown below and was wondering how I could change this so that iterable() is not called upon in the main. I would like to be able to make a method that returns an instance of a class that implements the Iterator interface hopefully an inner class. This is because my program will not have a main and will be supplied with a main that includes a new Object with will use the iterator method.
import java.util.*;
public class IteratorDemo {
public static void main(String args[]) {
// Create an array list
ArrayList al = new ArrayList();
// add elements to the array list
al.add("C");
[Code] ....
This is all I have been able to understand from what I want to do. This does not work and this is what I am trying to achieve
public class MyArrayList implements Iterable {
public static final int DEFAULT_SIZE = 5;
public static final int EXPANSION = 5;
private int capacity;
private int size;
private Object[] items;
[Code] ...
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Feb 23, 2015
I am working on a project and it asks me to "Provide appropriate names and data types for each of the instance variables. Maintain two GVdie objects" under class fields. I am unsure as to what is being asked when asking for two objects as instance variables and how I would write that...
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Feb 5, 2015
Let's pretend I'm working on an RPG. Like in all RPGs, there are items found all throughout the imaginary world. Each player and NPC can obtain an item. My question will concern those items.
In other words, I'd like to use instances of a class in multiple places of the code. Each instance will have its own, individual values of instance variables, with one obvious exception: itemQuantity should have a different value in playerInventory, npcInventory, etc. Also, I'd like a list of all items that can be found in the game. This list doesn't need itemQuantity at all.
class Items {
String itemName;
float itemWeight;
int itemQuantity;
[Code] ....
The question is: should I really make itemQuantity an instance variable of the Item class? It seems as though for each copy of the Item class I should create a separate copy with different value of itemQuantity, but that's not very efficient. Where is the error in my logic?
What's important is that there may be plenty items in a game and a player may be given power to create new items during the course of the game.
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May 6, 2015
Alright, I have a JavaFX gui that is creating a new instance of data calculation to graph in a chart; however, the data is not updating each time the Platform.runLater() feature executes. Each time an event occurs, a new instance with the same variable name occurs. I use to get methods to retrieve the data I want, so shouldn't the values update each time the new instance is created? This is a very condensed version of what happens with the event, but this is what is not working correctly.
Event:
solarPlot = new SolarTracker();
solarPlot.getElevation();
solarPlot.getAzimuth();
Class constructor :
public SolarTracker() {
[Code] .....
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May 23, 2014
Is there anything wrong on my code?
import java.util.*;
public class Card
{
private String description;
private String suit;
private int value;
private static final String [] cardName {"Ace","Two","Three","Four","Five","Six","Seven","Eight","Nine","Ten",
"Jace","Queen","King","Joker"};
[Code]...
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Mar 25, 2014
I'm having trouble to fully understand the difference between instance and class variables.
I though it was all about the static, i.e:
int age; // instance variable
static int age; // class variable
What's behind this?
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Jul 10, 2014
Implementation that proves that instance variables are not thread safe ....
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Mar 7, 2014
I've Parent and child(extends Parent) class To initialize the constructors, I'm injecting from google.juice#injector. Let me show the code,
Parent.class
public class Parent{
private Animal animal;
@inject
Parent(Animal animal){
this.animal = animal;
[code].....
When I do this, ClassCastException is happening. Why is it so? Is there any way to convert instance of parent to child instance.
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Aug 8, 2014
I have a managed bean for a form. I map the fields filled in the form with managed bean properties. when I submit the form and click new form , values from the previous form submitted gets displayed in the input fields. I used the scope of the from bean to session. what should be its scope so that values should be destroyed after I submit the form .For every new form ,new bean has to be initialized. On submit I navigate to another bean with session scope.
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Jan 13, 2015
I want to initialize my servlet based on the scope of my application.
For example, I have multiple admins with their respective email address.
I want to perform action within my servlet based on the given environment.
Would this be the right approach, if I set the admin email addresses in my web.xml as init-param:
<servlet>
<servlet-name>ServletName</servlet-name>
<servlet-class>com.mkyong.ServletDemo</servlet-class>
<init-param>
<param-name>admin1</param-name>
[Code] .....
Now if I am in the admin 1 environment, I would initialize my servlet with request parameter admin=1 and the servlet should load email address of admin 1 and similarly when in the environment 2, should load the servlet with admin 2.
call environment 1:
/servlet/Demo?admin=1
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws IOException{
[Code] .....
I could do the same by putting the email address of the respective admin as request param value, but i don't want to the email address to appear in the url.
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Jun 3, 2014
I have a hyperlink say,
[URL]
now, i want to access a managed bean's method to execute a service call related to the code embedded in the hyperlink.
My Managed bean
@ManagedBean(name="details")
@SessionScoped
public class XXXX extends Bean implements Serializable{
public XXXX(){...... }
public myMethod(..){
service.getDataRelatedToHyperlinkCode(....passing code here to fetch details from DB)
}
}
if i use postConstruct annotation it is getting executed only once since it is a session scope. and point to be noted is i cannot use viewscope and requestscope.
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Jul 3, 2014
I have an issue with variables/attributes scope inside a jsp tag file.
In short, I have a tag with an attribute named "id". If the page using my tag has a variable called "id" (maybe coming from the spring model) and I call my tag WITHOUT specifying the id attribute, inside my tag I still can acces to the "id" attribute that was defined in the page but I don't want this behavior; if the tag is called without the "id" attribute then it should defaults to empty/null.
Example:
print.tag
<%@ attribute name="id" required="false" type="java.lang.String" %>
id=${id}
site.jsp
(...)
The id is: ${id} // <- Prints 'X'
<my:print /> <- Prints 'X' ! I want it to not print anything in that case
<my:print id="Y"/> <- Prints 'Y'
(...)
What I want is to have the tag attributes live only in the tag, without having any knowledge of any variable outside of the tag itself. Is it possible?
My current workaround is to remove the "id" attribute, enable dynamic attributes and with a scriptlet search in the dynamic attributes map for the "id" and save it in a variable with a different name (e.g. "__id").
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Jan 30, 2014
I am trying to restrict the number of views in JSF 2.0.2 using
<context-param>
<param-name>org.apache.myfaces.NUMBER_OF_VIEWS_IN_SESSION</param-name>
<param-value>5</param-value>
</context-param>
In my case my managed bean is View Scoped and it supports a UI page which has multiple forms and each form is submitted as AJAX POST request.
As per the statndard, setting restriction to 5 should create 5 views and after that based on LRU algorithm the oldest views should get deleted if 6th views is created.
Therefore any action on the oldest view will throw the ViewExpiredException and i simply redirect the user to view expired page.
1) When i set the restriction to 5 views, i open 4 tabs with 3 forms each.
2) I submit the 3 forms on first tab everything works fine.
3) As soon as I go to 2nd tab and submit the first form thr, i get view expired exception
4) It seems I am exceeding the number of views I mentioned in web.xml
I want to know :
1) Does every AJAX POST submit itself creates a view ?
2) How I can count the number of views created in a session ?
3)Can i force expiry of a view in JSF 2.0.2 while the session is still alive ?
4) Normally JSF 2.0.2 session cachces the views. Lets assume session is alive the entire day but a view was created in morning at 9:00 AM and is not used again the entire day. Assuming that session doesn't reaches the max number of views it can save in entire day, will the view created in morning expire on its own after certain interval of time ? If not , can we still force its expiry while keeping the session alive ?
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Jun 9, 2014
Below code gets printed as output?
public interface I1 {
public void method();
}
public interface I2 {
public void method();
}
public interface I3 extends I2, I1 {
[Code] ....
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May 21, 2014
Given the case I have an object which is assigned only once. What is the difference in doing:
public class MyClass {
private MyObj obj = new MyObj("Hello world");
private MyClass(){}
//...
}
and
public class MyClass {
private MyObj obj;
private MyClass(){
obj = new MyObj("Hello world");
}
//...
}
Is there a difference in performance or usability? (Given also the case there are no static calls expected) ....
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Oct 27, 2014
The term "Local variable" is related to scope. That is a local variable is one which is defined in a certain block of code, and its scope is confined inside that block of code.And a "Member variable" is simple an instance variable.
I read in a discussion forum that when local variables are declared (example code below), their name reservation takes place in memory but they are not automatically initialized to anything. On the other hand, when member variables are declared, they are automatically initialized to null by default.
Java Code: public void myFunction () {
int [] myInt; // A local, member variable (because "static" keyword is not there) declared
} mh_sh_highlight_all('java');
So it seems that they are comparing local variables and member variables. While I think a member variable can also be be local in a block of code, isn't it?
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Jan 11, 2015
Given a reference variable : Car c1 = new Car();
when we create another variable and set it equal to the first : Car c2 = c1;
we're pointing c2 at the same car object that c1 points to (as opposed to pointing c2 at c1, which in turn points at the car). So if we have code like,
Car c1 = new Car();
Car[] cA = {c1, c1, c1, c1};
are we doing the same? Are we creating four *new* reference variables, each of which points at the same car (again as opposed to pointing them at c1 itself)? I think so, but want to make sure I'm understanding this correctly.
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May 23, 2014
I have a JFrame jf and JPanel jp on it. jp has five TextFields named cel1, cel2.. cel5. I wish to construct a String Cel + for loop index and run a for loop to reset the values of all the text fields using a single statement such as cel1.SetText("abc"). Similar things can be done in foxfro. How does one do it in java?
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Jan 16, 2015
in a set of instructions they keep referring to instance versions of things I've heard of before ie "private instance array of String references" (wtf is a string reference?) or "instance string variable" so what does all this mean?
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Sep 18, 2014
.I was reading head first java book and saw a barbell question on page no. 280,question-"what if you want to write a class in such a way that only one instance of it can be created,and anyone who wants to use an instance of the class will always use that one,single instance?"
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Apr 7, 2013
In the following example, I compute new_amount_d in 2 different ways and I get 2 different values although it should be the same in theory.
Is there a way to get the same value with BigDecimal for instance?
public class num004
{
public static void main(String[] args) {
double amount_d = 1000;
double interest_rate_d = 0.03;
[Code] ....
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Feb 23, 2015
I have a method that accepts JSONArray as parameter and returns the values of it as ArrayList Object. My question which of these ways is appropriate in populating the ArrayList object this method populates the arraylist upon creation of object (I don't know what the right term to use, but as netbeans IDE suggest, JSONArray object should be final since it was used in inner class.).
private List<String> getStringList(final JSONArray jsonArr) {
return new ArrayList<String>() {
{
try {
for (int i = 0; i < jsonArr.length(); i++) {
add(jsonArr.getString(i));
}
} catch (JSONException ex) {
ex.printStackTrace();
}
}
};
}
this second method is the usual way of populating collection
private List<String> getStringList(JSONArray jsonArr) {
List<String> strList = new ArrayList<String>();
try {
for (int i = 0; i < jsonArr.length(); i++) {
strList.add(jsonArr.getString(i));
}
} catch (JSONException ex) {
ex.printStackTrace();
}
}
What are the advantages and disadvantages between the two? like which is faster? or which consumed larger memory?
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