Superclass Variables - Subclass Access
Apr 13, 2015
So far I thought that setting superclass member variables as protected would allow the subclasses to access them using this. and that this was a good approach. However now after further reading am finding that actually these variables are better set as private and then accessed by the subclasses using public method (getters and setters) or constructor.
So my question is do you recommend setting them as private instead of protected and what would be the best way to access these variables from the subclasses ?
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Dec 2, 2014
how to get access from variables in a super class or a subclass. Here is what I got:
1) I have a super class that is in Jar file, I created a link in Eclipse, I know that the link is created correctly, I am going to concentrate just in one variable, so I don’t have to put all the code here firstName; in the super class(the one that is define in the path)
public class CommissionEmployee {
// Field descriptor #6 Ljava/lang/String;
private java.lang.String firstName;
in my class i have 6 argument constructor
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Mar 14, 2015
I am trying to display the getCommands() method from my subclasses but I do not know how to cast them both. At the moment I can only display one animals getCommands() method.
public class Test {
public static void main(String[] args) {
Pet [] pet = new Pet[5];
pet[0] = new Dog("Scamp", 1, "run");
pet[1] = new Dog("Molly", 2, "fetch");
pet[2] = new Dog("Rover", 3, "dig");
[Code] ....
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Oct 2, 2014
I am trying to prepare for the next installment Java course. I found a syllabus online from last year. All I'm trying to say is that I am not in this course but will be shortly. I tried the first project but I am having subclass issues. I want to access the getStock method in the Executive subclass from the client. I keep getting a cannot find symbol: method getStock from class Employee. I don't know why won't access Executive.
Main:
import java.util.*;
public class EmployeeClient extends Employee {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
//variables
String name = " ";
int totalSalary = 0;
int stock = 0;
[code].....
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Sep 10, 2014
I have a class called Sprite which extends its several subclasses. Therefore, there are a lot of different Sprite classes, the thing is however, most of those subclasses have unique types of variables which I want to only be included in those particular subclasses, not anywhere else. For instance, I might have a variable measuring distance in one subclass, and in another subclass there might be a height variable inherent. I don't want the first subclass to have both variables, neither the second or the main class. Because before I initialize my subclasses, I need to create the constructors of those subclasses in the main Sprite class first because it doesn't have the unique variables which those classes consist of. How do I prevent that? Now I have to create the unique constructors and variables for every subclass, when I only want them in their associated classes.
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Oct 4, 2014
I will like to add to the questions about constructors and its this. I have a class A with a constructor, i have a class B which initialize the constructor. also i have a class C which needs a variable in class A but doesn't need to initialize the constructor of A. the question how do i access the variable of class A without initializing the constructor.
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Aug 15, 2014
Does a variable have public access modifier? if we can use it within the class and outside of the class then can i access a public variable as follows??
class mo
{
void display() {
public int a=9;
System.out.println(a);
}
public static void main(String[] args) {
mo m=new mo();
m.display();
}
}
ERROR:
It shows 6 errors :-O.
Error 1. illegal start of the expression
2. class,interface, or enum expected
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Jul 16, 2014
My understanding was I could override a method from the superclass, including with different parameters, but when I try to use super. it gives me an error the arguments have to match the superclass. But, if I do that it won't make any sense.
The first code below is the superclass. The issue I'm having is on the second code at lines 7 and 10. The ultimate goal is to make a new class where I'm able to display various packages with or without insurance.
public class Package {
double shippingWeight;
public char shippingMethod;
final char air = 'A';
final char truck = 'T';
final char mail = 'M';
double shippingCost;
[code]....
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Jan 23, 2014
I've a question regarding polymorphism.
Is polymorphism possible only when the superclass is abstract?
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Oct 9, 2014
I would like to pass a variable I have in my main to my JFrame. In my main I calculate which pictures I should show in my JFrame. Is it possible to make objects of these pictures in my main class and use them in my JFrame? something like my code below.
public class JFrameTesting {
public static void main(String[] args) {
Image ImageVariable = Toolkit.getDefaultToolkit().getImage("C:1.jpg");
MyJFrame f = new MyJFrame();
f.setTitle("Drawing Graphics in Frames");
[code]....
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May 14, 2014
I'm using binding into fxml:
<Button fx:id="btnSalva" defaultButton="true" mnemonicParsing="false" disable="${controller.busy}"
onAction="#salva" prefHeight="57.0" prefWidth="141.0" styleClass="text-bold" text="Salva" />
Controller is my controller that extends another class from which it inherits busy property.
I see that fxmlloader only looks into the bottom class and not in superclasses, don't know if it's voluntarily or a bug.
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Apr 16, 2014
I have a superclass used for all the other entity
@MappedSuperclass
public abstract class BssStandardEntityLaravel extends BssStandardEntity
implements InterfacciaBssStandardEntity, Cloneable{
private static final long serialVersionUID = 1L;
@Column(name = "created_at", nullable=true)
@Temporal(TemporalType.TIMESTAMP)
protected Date created_at = new Date();
[Code] ....
When i try to read some data with a JPA controller, this error is raised:
Persistent class "com.bss.libbssabstract.database.entity.BssStandardEntityLaravel" has no table in the database, but the operation requires it. Please check the specification of the MetaData for this class.
org.datanucleus.store.rdbms.exceptions.NoTableManagedException: Persistent class "com.bss.libbssabstract.database.entity.BssStandardEntityLaravel" has no table in the database, but the operation requires it. Please check the specification of the MetaData for this class.
at org.datanucleus.store.rdbms.RDBMSStoreManager.getDatastoreClass(RDBMSStoreManager.java:702)
[Code] ....
It requires BssStandardEntityLaravel table like a normal entity. I used the same entity package in other applications and it works perfectly. Why this error is raised?
I use jpa2.1.0 and datanucleus to enhance classes
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Jul 3, 2014
I have a problem where I want to give each subclass of a certain class an index number (I don't care what index numbers are given, as long as there is a one-to-one relationship between subclasses and index numbers and the index numbers don't skip). This number will be used to sort the subclasses as an intermediate step to what I want to achieve. I know I could do this:
interface Superclass {
int index();
}
class Subclass implements Superclass {
int index() {
return 0; //or 1, or 2, ...
}
}
But this quickly gets tedious when I'm looking at lots of subclasses. Plus, there's the off chance that I could mess up and assign an index twice to two different subclasses by accident. Is there a better way to do this? I read about Annotations.
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Apr 21, 2015
I'm having a difficult time running this piece of my program. I can't run the method findSmallest() in subclass NEW because I receive an error that says I have to declare the variable "smallest" as final, but then I won't be able to continue my code because "smallest" when I happen to use "smallest" again, it will always be set to 0.
package FindYourCourseGrades;
import java.util.Scanner;
public class FindYourGrades {
public static void main (String[] args){
int number = 0;
int counter = 0;
int sum = 0;
double average = 0;
double smallest = 0;
[code]...
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Sep 17, 2014
There are a few things lacking in the TableView's keyboard navigation handlers. In tracing the code, the behavior is handled via TableViewBehavior and its super classes. If I want to augment that behavior, how do I do it?
Ideally, I would like to subclass TableViewBehavior, but I don't see how I can do it. This gets created in the TableViewSkin ctor:
public TableViewSkin(final TableView<T> tableView) {
super(tableView, new TableViewBehavior<T>(tableView));
...
}
but as you can see there is no factory method to create the behavior class. If there was, I could subclass TableViewSkin and override the factory method.
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Jul 9, 2014
The super keyword when used explicitly in a subclass constructor must be the first statement but what about if i have a this(parameters) statements ? As the this one must also be the first statement... Does this means that i can have only one or the other ? What about when the super constructor is not explicit (aka implicit ) , can i use the this( parameters) in the same constructor ?
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Apr 30, 2014
I'm working on a program design for a multimedia application its really just a learning process for myself about exploring application development, however there is a slight hiccup in the class inheritance hierarchy I think, and I'm not really sure why.
The problem being I cant set the constructor of subclass AnimatIntervalKeyFrame to be structured the same way as of the constructor of super class AnimatKeyFrame
This is the error given of the constructor of the subclass
public AnimatIntervalKeyFrame(int id, String category, Text text, ImageView image, int x, int y, int width, int height){
required: int,String,Text,ImageView,int,int,int,int
found: no arguments
[Code] ....
package multimediasoftware.appComponent;
import javafx.scene.image.ImageView;
import javafx.scene.text.Text;
// notes
// class is declared abstract
public abstract class AppComponent {
// variables
[Code] .....
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Nov 7, 2014
I am creating a set of 3 subclasses, 1 superclass, and an application. In my instructions it says to make set methods in my super and subclass by using dialog boxes. In the application you have 3 different arrays where you create objects and are supposed to call the methods from the subclasses to be used in the application. I don't know how to make the dialog boxes from my subclasses to show up in my application.
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Apr 9, 2014
I am trying to put a reference to a given subclass object into a linked list, and then come back later, and invoke a method of the subclass object that is in a given spot in the linked list. This produces an error because Object does not have that method. Is it necessary to cast the object to the correct subclass every time I want to use one of its methods, or is there a way to convince the JVM to treat it as always of type MySubclass?
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Mar 7, 2014
I have studied about the hierarchy of exception classes in which Throwable class comes at the top and two of its direct subclasses are Error and Exception..I just want to ask if in some code snippet we throw an instance of Error or its subclass within the try catch block then will that be also called "exception handling" ? I am asking this because Error class is not a child class of Exception therefore cant be said an Exception, therefore handling the same should not be called exception handling
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May 30, 2014
Using java to access SAP? I want to create a UI to analyze SAP data and create JTable reports. Not finding much on the internet.
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Nov 24, 2014
I am deploy my project in a machine and access it through VPN. In one page i am sending parameters array through hidden input field. When i access it in process page through request.getParameterValues it return null values, you can see it in attachment.This page work fine without VPN.
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Mar 30, 2014
Let's get it out of the way -- I'm stumped. On something that should be pretty simple to solve. Code follows.
public class Sum {
public static void main(String [] args) {
Double nSum = 0.0;
Double aDouble = 100.0;
for (int i = 0; i < 1000; i++){
nSum += 0.1;
[Code] ....
The output:
100.000000
100.000000
false
false
false
false
false
Process finished with exit code 0
I wrote another simple program and hardcoded the values: aDouble = 100.0; bDouble= 100.0000
Using aDouble.equals(bDouble) returns true, just as one would expect.
So what am I overlooking?
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Feb 25, 2014
Having two values
<c:set var="var1" scope="view" value="#{ID1}"/>
<c:set var="var2" scope="view" value="${ID2}" />
I tried in <c:if test=${var1 == var2}>
and eq also
above condition is not working. Both are same object. How to check?
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Apr 8, 2014
New to java/programming and i cant understand why the pen variable does not display the the correct value ... For example for input 1 ; 2 ; 3 ; 4 both variables will display 10 and i dont understand why pen does not have the value 6 .
import acm.program.*;
public class Chap4_ex12 extends ConsoleProgram {
public void run () {
int pen = 0;
int r = 1;
int sum = 0;
while (r !=SANTINEL) {
r = readInt(" ? ");
pen=sum ;
[code].....
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Jan 21, 2015
Variables defined in interface are public static and final so I was thinking that we should not be able to override the variables in a class thats implementing the interface. But when I am compiling the below class, it compiles fine and gives the correct values. but when I did disp.abhi = 35; it gives a compile error (cannot override final variable)
interface display{
int abhi = 10;
void displayName();
[code]....
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