Extending And Inheriting Classes
Jan 30, 2015
My teacher told me : It looks like everything is working except that in the Box, the method returns true if it is not a box.
The only other thing missing is the if statements in the main method using the .equals() method to do the comparisons. But, now I am lost on how to do my if statement.
HTML Code:
private int height;
/**
* Constructor for objects of class box
*/
public Box3(int l, int w, int h)
{
// call superclass
super(l, w);
// initialise instance variables
height = h;
[Code] ....
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Jul 3, 2014
I am working on a project involving a class that has the attributes of one of its inner classes. Now, if possible, I would like to make it so that the inner class is not visible outside of the class. Also, some of the functional mechanics require that the class be an instance of the nested inner class (it extends the inner class). The following code snippet demonstrates the situation.
public class A extends A.B {
public static class B { //ideally I would like this to be private/protected.
}
}
When I try to compile this program, I get the error message "Cyclical inheritance involving A." This error does not make much sense because, since the inner class "B" is static, it requires no instance of "A" (it does not inherit from "A" or uses it). My question is "Is it possible to do something similar to this structure?" I have searched many forums in search of the answer but have not found anything that attempts to explain it. The closest problem that I have found is one relating to the inheritance of a nested inner class from another class. I would like to express that the problem that I am having involves a class defined within the inheriting class.
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Sep 20, 2014
Basically I want to make a class called library, but I don't want to make an interface because I actually want to define the methods. I think I can only use abstract classes but not really sure how to use those. But I still have a problem, I want to create a Map that classes implementing Library class have to have in their code, and the Map will be a HashMap with <String, ParentClassHere>, so basically let's say I make a class called Car, implemeing Library to the Car class would create a Map library = new HashMap<String, Car>. Can I do something like this? And also include methods to get values and set values to the library Map?
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Jan 4, 2015
I have a working program, except that it does not calculate the credit hours and the financial aid. When I enter an input, it works, until it should show the student name, credit hours and financial aid. the error i get from the command is "Hours invalid for false student". Here is the program i think i might have the problem.
import java.text.DecimalFormat;
public abstract class Student
{
//initialise variables
String name;
int creditHrs;
[Code] .....
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Mar 12, 2015
1. Tried to use setLayout() but it wouldn't let me. Have imported libs
import javax.swing.*;
import java.awt.*;
but it doesn't work. It only worked when I extended a class with JFrame. Why do I have to do it? I already have a JFrame instance:
public test(){
JFrame frame = new JFrame();
frame.setTitle("Workshop");
frame.setBounds(500,300,400,300);
frame.setVisible(true);
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
....
}
This code runs smooth, so it's confusing for me that it lets me create a JFrame object, and put buttons onto it, but it wants me to extend the class onto JFrame class in order to use a method.
2. I've read somewhere that AWT is old and should not be used anymore. Is there a diagram or a list with objects and properties that are manipulated only by Swing so that I could concentrate only on those? For example (made up list):
JPaper -
- width, setWidth(x)
- height, setHeight(x)
- position, setPosition(x,y)
- color, setBackground(RGBa)
- acquire, add(subordinate component)
- deprive, remove( subordinate comopnent)
- etc...
JSticker -
- width ...
- height ...
- write, setText(String)
- etc...
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Dec 1, 2014
I have a Member class and a Player class. Players extends Members. I know that player will have all the methods of Member but I was wondering how I could link a player object directly to a member object.
public class Member(){
String name,surname;
public Member(String name, String surname){
this.name = name;
this.surname = surname;
[Code] ....
What im looking for is the p1.getName() to return John. Can I do something within the Player class for it to inherit from a Member object...
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Jul 25, 2014
Really need some simple and complete example on how to extends components (graphically and functionally) for primefaces 5.
For example I can't figure how to add custom attributes to existing component or define default values for existing attributes.
Is there any tutorial or a basic common way to achieve this goal or each component have to be extended in its way?
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Oct 21, 2014
I am writing a program that should take a url and scan the page for any links. It is in the beginning stages, but I ran into an error when I tried to extend a class. There's a lot going on in this code, but the error is caused by the constructor.
Error message at compile time:
"constructor Page in class Page cannot be applied to given types;
{//Constructor
^
required: String
found: no arguments
reason: actual and formal argument lists differ in length".
Here's the code(first my class, then the class I extended)
public class SearchEngine extends Page {
public static Color customGreen = new Color(69, 194, 33);
public static Color customYellow = new Color(232, 166, 12);
public static Color customBlue = new Color(25,97,255);
public static Color customYellowComp = new Color(178,125,0);
[code]...
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Apr 10, 2014
Java Code:
public class Game extends Canvas implements Runnable, KeyListener {
private static final long serialVersionUID = 1L;
public Game() {
setMinimumSize(new Dimension(width, height));
setMaximumSize(new Dimension(width, height));
setPreferredSize(new Dimension(width, height));
}
[code]...
I want to remove the extends Canvas from the top line and when I use JFrame to add canvas, I don't do add.(this, but instead I do add a canvas variable I make. So instead of extending I want to make a variable. But then how would I do the start, stop and run?I want to use Graphics, Canvas (Not Jpanel because I want to use BufferedImage) & JFrame. I don't want to extend Canvas, how could I use Canvas identically to shown above but instead of extending using it as a variable? or, how could I do this?
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May 26, 2014
I'm having a problem with SplitPane (horizontal Flow). What I'm looking for is to find a way to maintain the left pane in the same position when the main window maximizes. I do not want the left pane to grow on its width. If I go into the AnchorPain Constraint in the Scene Builder and remove the right and left constraints, when I run the application, the left pane keeps its position, but it appears a gap between the two panes (the left pane and the right one).
I need to find the way to expand the right pane to the position where the left pane is.
The link shows an image that illustrates the problem. [URL]
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Oct 18, 2014
What is the difference between extending JFrame in one class and simply constructing a new JFrame object in that same class? What benefits do I have with each solution, providing I want to use that class to create the GUI. Is it the same or are there differences rather than not having to reference to a new JFrame to be able to use its functions?
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Feb 14, 2014
I am new to java and during my classes we built a basic calculator. I want to extend my calculator and added function to square numbers.Here is my program:
Java Code:
package calculator02;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
[code]...
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Apr 26, 2014
I've been trying to pull data from another class file "Calculations.java" and have it be displayed in a TextField in "DataAnalyzerGUI.java". Here is how the hierarchy is broken down for my assignment:
DataAnalyzerGUI.java extends JFrame
ReadFiles.java extends DataAnalyzerGUI.java
Calculations.java extends ReadFiles.java
Everything displays and functions correctly in a command prompt if I use a line like this:
System.out.println ("Lowest opening " + dateArray[lowestOpenIndex] + ": " + dataArray[lowestOpenIndex][2]);
But trying to get it to display in a GUI has been quite troubling.
I know the code is supposed to look something like this:
dataOutput.setText(DESIRED CODE HERE);
But I am unable to find anything of value to work out.
I have attached my complete project....
Attached File(s)
Assignment 4.pdf (247.05K)
Assignment 4.zip (235.81K)
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Apr 18, 2014
How do you call classes within other classes? Or can you only call classes through the main?
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Feb 14, 2015
I'm doing an aggregation exercise that's suppose to find the volume and surface area of a cylinder. What I'm trying to do is pass values from one class, to a second class, and that second class passes values to a third class.
This may be a clearer explanation: The first class is the main program which sends values to the second and third class. The second class is used do calculations for a circle (a pre-existing class from another assignment). The third class grabs the values that the second class calculated and calculates those values with the one that was passed from the first class to the third class. The first class then prints the outcome.
Problem is when the program gets to the third class, it just calculates the value from the first class with the default constructor from the second class. It's like the second class never received the values from the first class. I think I'm missing a step, but I don't what it is.
First Class:
package circle;
import java.util.Scanner;
public class CylinderInput
{
static Scanner in = new Scanner(System.in);
public static void main(String[] args)
{
//user defined variable
[Code]...
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Dec 26, 2014
Why do we get such output or which line of code produces the output?
1class Egg2 {
2 protected class Yolk {
3 public Yolk() { print("Egg2.Yolk()"); }
4 public void f() { print("Egg2.Yolk.f()");}
5 }
6 private Yolk y = new Yolk();
[Code] ....
/* Output:
1.)Egg2.Yolk()
2.)New Egg2()
3.)Egg2.Yolk()
4.)BigEgg2.Yolk()
5.)BigEgg2.Yolk.f()
*///:~
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Oct 18, 2014
I'm quite new to Java. I have some trouble with understanding how to get two classes to get objects from each other (if that is the correct term).
Lets say I have a login class, in which I have a method checking what the user has entered into the console (I have not displayed the whole code, but this class works as it should and give the user an option to enter username and password and return it true if entered correct).
public static boolean validateUserPass(String userName, String password) {
String[] user = {"admin"};
String[] passwords = {"firkanten"};
boolean check = false;
for (int i = 0; i < user.length; i++) {
if (userName.equals(user[i])) {
if (password.equals(passwords[i])) {
check = true;
Now, in another class I want a display box to appear on the screen and give the user three options: Click yes, no or cancel. I get this to run perfectly alone, this is not the hard part for me. I want the display box only to appear when the correct username and password is given, but I can't seem to figure out how to do this probably.
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Feb 7, 2014
Regarding the code examples in Head First Java, this is from Chapter 5, regarding the beginning creation of the dot com game. There are two classes in quesiton
the first is the SimpleDotComTester class:
public class SimpleDotComTester {
public static void main(String[] args)
{
SimpleDotCom dot = new SimpleDotCom();
int[] locations = {2, 3, 4};
dot.setLocationCells(locations);
String userGuess = "2";
String result = dot.checkYourself(userGuess);
}
}
and the second one is the code for the checkYourself () method in the SimpleDotCom class
public class SimpleDotCom {
int[] locationCells;
int numOfHits = 0;
public void setLocationCells(int[] locs)
[code]....
Now I noticed that both classes use a variable called result; the program runs fine, but assume from the example that you can use the same variable name two different classes;
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Mar 29, 2014
design a class to conduct a survey of three hospitals. you want to know how many sectors (eg operation, children, gastronomic) each hospitals have, and how many doctors there are in each sector.
what is the process of class design?
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Jan 5, 2014
I have a Date class and Time class. Is it possible to pass Time object inside Date constructor so that toString function gives output as 12/05/2013 06:31:30 ?
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Apr 24, 2014
I have two classes.
First and Second.
In First class I want to use methods from Second class. So:
Java Code:
Second s = new Second();
s.secondMethod(); mh_sh_highlight_all('java');
Second thing I want to do is use JTextArea from First class in Second class.
So since it gives me error, I extended First class with Second:
Java Code: public class Second extends First { mh_sh_highlight_all('java');
It look like it should work, no errors etc. Also both things are working separately. But since I used both at once...
Java Code:
Exception in thread "AWT-EventQueue-0" java.lang.StackOverflowError
at package.Second.<init>(Second.java:7)
at package.First.<init>(First.java:17) mh_sh_highlight_all('java');
I can move what I need to First class, and it will work fine, but I want to make this in two classes. But I really don't understand extends, I just use them if there is need for them. So I don't know how to handle this problem.
I also tried to extends Second just like First:
Java Code: public class Second extends JPanel implements ActionListener { mh_sh_highlight_all('java');
Instead of extending First, but it can not be done, since ActionListener is in First...
Well. Also addActionListener can maybe solve my problem?
I'm using:
Java Code: xx.addActionListener(this); mh_sh_highlight_all('java');
Maybe I can use something instead of this? But what?
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Jan 19, 2015
Wondering, what is exactly reason for existence of inner classes? Are there problems that without them you can not resolve?
Anything beside emulate multiple inheritance - when your class need to extends the real classes, and not implement multiple interfaces ?
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Mar 28, 2015
I have a folder of classes that I am packaging together. Some classes are being packaged and compiling just fine. My other classes in the same package, however, are saying that they cannot find these classes.
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Apr 12, 2015
What i'm trying to do is to pass a bufferedreader string from main method to a class that will set on how fast or slow a message will be displayed but it has to be displayed on a JTextArea that's in a constructor class.
import java.awt.*;
import javax.swing.*;
public class demo {
JFrame frame = new JFrame ("Idle Game Test!");
JPanel backGroundPanel = new JPanel ();
JPanel statusPanel = new JPanel ();
JPanel buttonPanel = new JPanel ();
JPanel bigPanel = new JPanel ();
JTextArea message = new JTextArea ();
[code].....
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Aug 7, 2014
So I prefer to use Emacs rather than using Eclipse or some other IDE and I am wondering how to include external classes in my main file?
For instance I have my main file (the one that includes my 'main()' function) and then I have another class (seperate file(s)) for creating a GUI, or making a game and using a Player class, Weapon class, etc. How can this be done? Do I just use 'extends myclass'?
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Jan 21, 2014
I would like to use the attribute A of my class Selecter1, in my main class Resizing. How?
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