Effect Of Hiding In Polymorphism
Aug 25, 2014
I have difficulty understanding the following behaviour.
class A {
public String string = "a";
public String toString() {
return string;
}
}
class B extends A {
[code]...
The output of the program is 'c'. This is expexted behaviour. But if class B is changed as follows,
class B extends A {
public String string = "b";
}
Now the program prints 'a' instead of 'c'. Why the statement: b.string = "c"; is not taken into account?
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Feb 17, 2015
Recently I have been thinking of using additional interfaces in one of my libraries to hide certain "unsafe" methods of my classes from the user. I would like to get the opinion of other, more advanced java programmers on this issue.
What I do is something like the following (heavily simplified):
public interface ReadOnly {
public int getValue();
}
public interface ReadWrite extends ReadOnly {
public void setValue(int value);
[Code] ....
The user would have access to the ExternalInterface. The ExternalInterface is controlling the values of the InternalComponent. The user can get the InternalComponent, but typecasted to a ReadOnly which does not expose the setters.
Now the thing is the user can still access the setValue method by typecasting the ReadOnly to an InternalComponent or to a ReadWrite, and that is not bad. If the user knows exactly what he/she is doing this will give him/her more flexibility and more power. But this way it *should* become obvious that this is not the intended use and perhaps the extra work of typecasting will discourage the user from doing this.
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Sep 26, 2014
I am thinking of creating a quiz application and facing one problem.
On first question I don`t have to show previous button and on last question I don`t have to show next button.And for in between question I have to show both the buttons.
.
How can I do that in a JSP page.
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Apr 15, 2014
I'm creating a game called Mouse Trap and I'm having an issue with a graphic drawn using AWT. Basically, when the mouse collides with the cheese, I want the cheese to disappear, or call (cheese[i].hide()). However, the cheese does not appear. hide() works for all other objects that inherit from PFigure, but the cheese will not. It's created a major issue in my game, and basically the only task left to accomplish.I believe my problem lies within Cheese.java, method draw(). For example, if I replace it with an example drawing, this problem goes away!:
public void draw() {
Graphics g = panel.getGraphics();
g.setColor(Color.blue);
g.drawOval(x + width / 4 , y + 1, width / 2, height / 2);
[Code] ....
I have three classes below that most likely involve the problem, feel free to ask if you need the others.PFigure.java (This class cannot be changed as a requirement to my project)
import java.awt.*;
public abstract class PFigure implements Comparable {
protected int x, y; // Current position of the figure
protected int width, height; // Drawn (displayed) this size
protected int priority; // Can use to determine "winner"
protected Panel panel; // Panel the figure lives on
[code]....
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Mar 21, 2015
I have my code in 3 different files using encapsulation (Data hiding) and i have 1 problem at the very end of my code in my if and else statement (very bottom) when trying to call the classes from the other 2 documents. I will put the code in 1st document to 3rd document.
// FIRST DOCUMENT
public class CollegeCourse { //class name
//variables
String deptName;
int courseNum;
int credits = 3;
double fee;
[Code] ....
UPDATE: error message is
UseCourse.java:24: error: cannot find symbol
LabCourse lc = new LabCourse(department, course, Credits);
^
symbol: variable department
location: class UseCourse
UseCourse.java:24: error: cannot find symbol
LabCourse lc = new LabCourse(department, course, Credits);
[Code] ....
4 errors
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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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Jan 29, 2015
While studying polymorphism , i have some doubts that i am unable to clarify ..... Here they are :
Suppose our inheritance ladder be :
C1 <- C2 <- C3 <-....... <- C100
where C1 is most general (superclass) and C100 is most specific class .
Now , if i write java code in my main() :
C21 Obj = new C100();
Obj.someMethod();
So, what will happen in scenarios as given below :
Scenario - 1) If someMethod() is only defined in C1 ? How will compiler search for this someMethod() ?Will it be executed ?
Scenario - 2) If that someMethod() is static and only defined in C1 , then how will it be searched and executed ?
Scenario - 3) If someMethod() is only present in C100 , then what will happen ?
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Jan 13, 2015
I want a JLabel with scrolling text as marquee effect...
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Sep 18, 2014
I have a program I want to make (text based, no gui). There is the main class, an Employee class (sort of a template), a CrewMember class, and a Manager class.
I'll put the code for each class an explain the problem I have.
package polymorphism;
import java.util.Random;
public class Start {
public static void main(String[] args) {
Random rand = new Random();
Employee staff[] = new Employee[5];
for(int i = 0; i < staff.length; i++){
[Code] ....
Some of the code is a bit incomplete simply because I ran into the problem. As you can see I made an array in the Start class and it holds objects of Employee type, but create a new instance of either a crew member or a manager, sets their wages, hours, and bonus if applicable. I know if I create an array of a certain type, I can't call upon the subclass' method (Manager in this case) because it has a new method that I added. What I'm trying to do is pretty much call upon the getSalary() method in the Manager class/object, but of course I can't. What way would i be able to do that? I tried looking for some answers. I read about making the superclass abstract and implementing it into the subclasses. Would that be an option?
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May 31, 2014
I would eliminate the ifs and elses using polymorphisms that solves this lot of ifs? How could I solve this?
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Mar 2, 2014
In carrying out my little game I made a panel "Winner" in which I have two JButton plus I would like to add a blinking text to indicate the victory of the player("You win!"). Currently this text is static, designed by the function drawImage. How can I make it "flashing" maybe alternating the vision of the text (which I present in two different colors)?
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Jul 3, 2014
I am working on a game project. Whenever we are starting our game application in production, it works perfectly around 3 days after 3 days, CPU utilization is increasing upto around 95% to 99% and application stops to respond. Before 6 days, I started application again and we doubled our Perm Gen memory size. The same problem happened but it happened after 6 days.
Now, i am not able to relate CUP utilization to Perm Gen memory. Is Perm Gen memory effect CPU utilization?
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May 24, 2014
I am using something a kin to this:
for (int w=0;w<bi.getWidth();w++) {
for (int h=0;h<bi.getHeight();h++) {
int color = bi.getRGB(w, h);
color = color << 5;
bi.setRGB(w, h, color);
}
}
I am using a solid green image so
11111111000000001111111100000000
I just wanted to see how it looked so bumped it over 5 places (obviously changing the color). To my surprise, there was no added transparency. I mean moving it to the left would make the alpha:
11100000
I am thinking that setRGB() doesn't effect alpha. Is this accurate?Tested it and in fact setRGB has no effect on the alpha bits. So now the question is how can I gain access to them. I am going to look into the writable Raster API. Perhaps, I can also use a modified awt to access directly OS data.
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Dec 3, 2014
I have one jsp page in which I have listed some service records fetched from Database. I have made one of the column, for eg. Service ID to be link, which should display all the details of that service when clicked. I want those details to be displayed in lightbox. I tried doing it but when any service ID link is clicked, it displays same(First Service in record) service details.How do I pass reference of that current service to lighbox effect.
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Oct 18, 2014
This isn't solely related to java.awt.Color, it's more of a question on how to store methods or redirections to use methods on any value passed in. To explain my question I'll describe a scenario:
ClassA is an instanstiatable class
ClassA has an instance of ClassB called cB
ClassA has methods of affecting cB
ClassD is also an instanstiatable class
ClassD has an Array[x][y] of instances of ClassA
I want to create a ClassE which I would initiate it with references to ClassA's methods or their actual methods and then I can use ClassE to easily transform ClassD's instances of ClassA by the same methods.
What I'm actually doing:
I made a class called GameColor, it has methods like changeHue, setRed, setHue, changeBrightness, setSaturation etc, these methods affect an instance of java.awt.Color in the GameColor class instances, so like they can change the hue or set it with changeHue or setHue etc...
Now I want to do something like perform a single method on a whole BufferedImage, on each of it's pixels RGB. So, I'm thinking of creating a GameColorEffects class which I store references or actual methods of GameColor like changeHue, and then I use GameColorEffects somehow to change a whole BufferedImage more efficiently, what's the most efficient way I can store methods or their reference of GameColor and then later apply them on each pixel of a BufferedImage using GameColorEffects. So all I do is initiate GameColorEffects with methods or reference from GameColor, and then I can apply it to easily transform each pixel.
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Apr 19, 2014
can we achieve runtime polymorphism by data members?
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Dec 14, 2014
I have a UI widget, like a table view for example, displaying real-time data. This table can be configured - so it has many properties. The way I would like to do so, is to have a small 'configure button', once clicked, would rotate the entire table along its y axis, and display another panel with checkboxes etc... So effectively, the hidden properties panel is revealed by rotation.
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Jan 9, 2014
Why is the equals-method in the super-class invoked? Shouldn't the equals-method in the sub-class be invoked(at least in the first if-statement since b2 is a B(i know B is also an A))?Is the equals-method overridden? Or does B have its own equals-method?
class SomeClass{
public static void main(String[] args) {
B b1 = new B(123,1);
B b2 = new B(123,2);
[code]...
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Jul 17, 2014
I am trying to understand the effect of calling real business logic from the test class. If I have a test class that call the service method which make update to DB. Is DB really changes through test class?
e.g.
Java Code: @Test
public void testUpdate() {
MyDto myDto = new MyDto(paramters to create new myDto object); //creating new dto object
myService.updateMyData(myDto); //passing new dto object for update (DB record really changed??)
MyDto testDto = myRepo.find(myDto.getKey()); //get record for the corresponding key
assert testDto.getSomeProp() == myDto.getSomeProp(); //what testDto.getSomeProp() return? new value send on myDto or old value from DB?
} mh_sh_highlight_all('java');
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Apr 14, 2015
I have a quick polymorphism question. I have a parent class and a sub class that extends the parent class. I then declare an array of parent class but instantiate an index to the sub class using polymorphism. Do I have to have all the same methods in the child class that I do in the parent class? Here is an example of what I mean.
public class ParentClass
{
public ParentClass(....){ }
public String doSomething(){ }
}
public class ChildClass extends ParentClass
{
public ChildClass(....)
[Code] ....
Is polymorphism similar to interfaces where the child class needs all the same methods?
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