Polymorphic Reference Doesn't Seem To Be Specific
May 18, 2015
Is there a short term that means: "using an object reference with the datatype of a supertype to refer to an object with the datatype of a subtype"?
Saying "polymorphic reference" doesn't seem to be specific enough because ALL references other than those with the Object datatype are polymorphic. I saw one post that referred to these reference variables as a "supertype reference." In the absence of any other (more official) term, I may just use that term because calling a reference a "supertype reference" implies that there is a subtype. It sure beats what I was thinking about using: "sub-as-super." Which, when the inevitable mispronunciations occur, would lead to all kinds of off-color jokes.
Is there an "official" term that all of the dozens of Java books I have read seem to have missed? Or does everyone stumble along, spelling things out with a nearly sentence-long phrase.
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Feb 10, 2015
the problem was :
i wrote it on paper with my examples.and just for laughts , i uploaded another picture that dont belong to my problem. its just my way to understand binary search tree implementation , so i wanted so share.just for laught : looks like the map of the universe.
now my problem : why after i changed Current to Current.left, Parent still has the value of root. i draw and wrote it on a paper. to be clear as possible - picture 2 :
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Aug 1, 2014
Why in this code testSon class void display() method is called instead of testFather class void display()
class testFather
{
void display() {
System.out.println("This is testFather class");
}
testFather() //testFather constructor {
display();
[Code] .....
Output : This is testSon class /* why not This is testFather class*/
This is cons of testSon class
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May 9, 2014
It seems we have abandoned Dice/Die(s), and are now working on something completely foreign. I don't even have a code to start with because I haven't the faintest clue what is going on here (no notes given on this topic, as usual). We are given 4 half-written programs to work with.
The instructions are:
"Examine the FormLetterEntry abstract class, and create the two derived classesTextEntry and DataItemEntry. Be sure to implement all the abstract methods in each derived class."
This is the code we were given:
package homework5;
import java.util.Properties;
/**
* Abstract class representing the entries in a form letter.
**/
public abstract class FormLetterEntry {
/**
* Retrieve the template string for this entry
* @return the value of this entry in a template
**/
[code].....
I understand (and correct me if I am wrong) that a derived class is a class that is created from a base class via inheritance. What I don't see are any notes on how to write a derived class. I see some notes online on how to do so, but they don't fit with what he's written above. What he means by "Be sure to implement all the abstract methods in each derived class."
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Jan 29, 2014
I am trying to write a specific byte sequence to a specific memory location on a removable storage drive. Does Java allow me a way to do this? I know the dangers in accessing memory, but the memory location of the data that will be written will never change.
how to assign a variable a memory location.
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Nov 5, 2014
How do I move focus from a jcombobox to a specific component say a jtextarea.
My attempt below seems to be moving to a random component not the desired jtextarea.
takenByCombo.addKeyListener(new KeyAdapter() {
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_TAB ) {
e.consume();
dayJTArea.requestFocus(); // focust not moving dayJTArea
}
}
});
I applied the above logic to move focus from a specific jtextarea to another jtextarea as seen below and it works as desired.
dayJTArea.addKeyListener(new KeyAdapter() {
public void keyPressed(KeyEvent e) {
if (e.getKeyCode() == KeyEvent.VK_TAB ) {
e.consume();
monthJTArea.requestFocus();
}
}
});
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Feb 9, 2015
So here we go with my problem:
- from the main class will arrive three variable (String name_used, int level_choose, int level_result)
I have a .txt file with this kind of formatting:
mario 1 1 0 1 0 1
carlo 0 0 0 1 1 0
...
Where I use 1 and 0 in the main for write if the level (you see that the numbers are always sixr? are egual to six level existing) BEFORE is done correct or wrong
- when in the main a user make a level a feedback coming back from the class level saying if the user made the count correctly or wrong. and i wanna replace the value (1 or 0) in the txt file with the new level result.
So i have all what i need as parameters i think.
name_used to look for the correct line in .txt file with .indexOf
level_choosed to go throught the correct index of that line
level_result (1 or 2) to be replaced with the existing one
Java Code:
public void salvaRisultati(String name_used, int level_choosed, int result_of_level) throws FileNotFoundException{
}
} mh_sh_highlight_all('java');
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Feb 8, 2015
I have some problem to understand the way to make this:
In my main class a user can save his name in a txt file (and the system initially will add 6 value equals to 0) than he can choose between 6 level and make it.
example of .txt file data:
mario 0 0 0 0 0 0
carl 0 0 0 0 0 0
AT THIS MOMENT i just made other class and they work, is this new one that is hard for me. I'm trying to make a class that:
1- (first method called verificaRisultati) take name_used and level_choosed from the main and go to check in the .txt file if that level before was done right(1) or wrong(0)
and return something like "before you made this level properly" or "before you made this level incorrectly" AND THEN let the user start with the level.
2- (second method called salvaRisultati) at the end of the level i wanna pass the result (correct/incorrect) to another method of this class that will save the value (1 or 0) associated to the user in the right position.
This is the class that i'm writing:
Java Code:
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
public class ResultUsers {
[Code] ....
I really need some hint and some code example because I'm stuck. How I can take exactly the line with the user name? How I can correctly split the line in an array and then read/modify the value for that level?
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Jan 27, 2014
I am doing a Junit test case, but I keep having issues with AssertEquals ( object expected, object actual). I don't know how to reference the other actual object so that it can compare to the expected.
public void add (Distance d) throws CustomException
{
//I can also convert feet to inches and add all inches together and then divided inches to feet and inches
Distance result = new Distance();
int newFeet = this.feet + d.getFeet();
int newInches = this.inches + d.getInches();
if(newInches > 11)
{
newFeet = newFeet + (newInches/12);
[Code]...
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Jan 24, 2015
I don't really know what this means and it is sending an error when I try to run my program I am trying to set the x and y value (Int x and int y) to setVisible false at a specific time in my game but it keeps sending the error that int is not a reference type.
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Aug 25, 2014
I'm fairly new to Java, I'm very experienced with C++ and C# in which you can pass by reference - extremely useful. Take for example this bit of code in C#:
class MyClass
{
public MyClass(int i)
{
m_i = i;
}
public int m_i;
[Code] ...
Just at the end of this program x.m_i will be equal to 8. As far as I can see this is not possible in Java: you can't pass a double by reference, using a Double will kick in the autoboxing so that won't work either. The only "solution" in Java would be to pass in a double[] (of length 1) or to make a wrapper class, both nasty solutions because a user may want to just hold a double as a member of their class just as I have, for reasons such as not allocating more memory for a class and generally not being bloated.
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Mar 15, 2015
I am making an MVC program and I am not allowed to put the action listeners in the view class. I was able to get one button working fine but since I am unable to reference them I cannot give them both individual responses.
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class Controller {
HobbyList model;
ListView view;
[code]....
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Apr 17, 2014
public class {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
double[] numbers = new double[10];
System.out.println("Enter " + numbers.length + "numbers");
for (int i = 0; i < numbers.length; i++) {
numbers[i] = input.nextDouble();
[Code] .....
I am trying to reference the input "numbers[i]" to my mean method, how do i do that?
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Nov 12, 2014
I know in C++ It's possible to pass by reference but what about java?
For example, can i pass the address of a health variable into a Ninja class and then
Since Ninja inherits from an enemy class pass the health into the enemy class and within there have a function that returns that same health address and takes 5 from the health returning 95.
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Aug 29, 2014
I passed my abstract class private final reference to another concrete class and I used abstract class reference as parameter to that concrete class constructor and in my main method and null to that parameter then only that program executes correctly...i placing my code below ..if there is any error tell me where is error occurring then i will check my code...i think my code is right but little bit doubt abstract class concept.
{
}
class concept1 extends concept
{
private final concept parent;
public concept1(concept aparent)
{
parent=aparent;
System.out.println(parent);
}
public static void main(String args[])
{
//concept p=new concept1(null);
concept c=new concept1(null);
}}
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Mar 29, 2014
When I write a statement such as:
myType x;
This means that x is a reference to objects of type, "myType" and no memory has been set aside for an instance of this object. I think it's true that x also has the starting memory address of this object.
What I feel uncertain about is if x is telling the JVM(?) where it can find the starting address of this object, why do we care about the type that x is?
i.e., if we assign x to an object totally unrelated to this type then the compiler would complain - correct? If so, how come, since all x is doing is telling the JVM(?) where to find your object (via the address it contains).
I suppose all, hy a reference has a type associated with it if all the reference does is point you to the object?
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May 17, 2014
I am currently learning Java basic concepts and this is a very simple code which produces error depending on the way I write. It is as follows:
package testPackage;
interface ArrayInsideClassShock {
}
class Check{
ArrayInsideClassShock var[]; //Error line
var= new ArrayInsideClassShock[10];
}
Error in eclipse:Syntax error on token ";", , expected
But if I write it as:
package testPackage;
interface ArrayInsideClassShock {
}
class Check{
ArrayInsideClassShock var[]=new ArrayInsideClassShock[10];
}
It doesn't show any error.
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Feb 15, 2010
what these mean with examples..
1. A reference variable can be of only one type and once declared, that type can never be changed(although the object it references can change)
2. A reference is a varaible ,so it can be reassigned to other objects(unless the reference is declared final)
3. A reference variable's type determines the methods that can be invoked on the object the variable is referencing.
4. A reference variable can refer to any object of the same type as the declared reference , or - it can refer to any subtype of the declared type.
5. A reference variable can be declared as a class type or an interface type. If the variable is declared as an interface type, it can reference any object of any class that implements the interface.
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Jan 23, 2014
I don't understand why following code when executed returns false
String s1= " string".trim();
if(s1 == "string"){
System.out.println("true");
}
else{
System.out.println("false");
}
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Jan 29, 2014
How can i check the reference that is not duplicate and date format is DDDCCYYnnnnnnn, CC must be 20 and YY must not be less than the current year, nnnnnnn is the sequetial number of the file and to complete the 7 numeric characters, zero's must be populated in front of the number. DDD must be a valid reporting entity code. there must not be a duplicate. Code I try
private boolean test-date()
{
String s_Ref = this.transactionFile.getsReference();
boolean flag = true;
if(!isValidPattern(s_Ref, "[0-9]{14}"))
[Code] ....
The reference number is like 201401030234509
If there is duplicate show error code 105
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Feb 28, 2015
I am unable to understand the meaning of this sentence "final reference variables must be initialized before the constructor completes.",What is trying to imply?
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Oct 30, 2014
I have started working on a little project in my free time. It is just a simple text rpg that runs in a counsel window. I have 5 files each file contains 1 class.
public class SomnusCharacter {
private String gender = "";
private int age = 0;
private String race = "";
private int level = 0;
private int xp = 0;
[Code] ....
The chain of events right now is:
1. MainMenu is run
2. If user inputs n CreateCharactor is run
3. User inputs name, age, ect in SomnusCharacter object made in CreateCharacter
4. Intro (just rough demo for testing purposes) is run
5. If user inputs m Menu is run
6. Menu calls and prints out all the information from the object made in CreateCharacter
Step 6 is where I am having my problems. How can I reference (lets say the SomnusCharacter object made is called player) player from my Menu class? I know that if I made a new character that it would just create another SomunsCharacter object with the default values again.
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May 22, 2014
I read somewhere : "Java use clone() method of Object class to copy content of one object to the other. The problem will arrive if the Class that needs to be copied also contains reference to the other object."Not able to understand the second line.
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Sep 30, 2014
How are methods invoked on the `bird` parameter?
next.xhtml:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:ui="http://java.sun.com/jsf/facelets"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:f="http://java.sun.com/jsf/core">
[Code] ....
`MyQueueBean` is intended to give out a bird once only, to exactly one end-user. Because it's application scoped, and not session scoped, getting attributes directly from the bean would give inconsistent results.
The birds application is from Facelets Essentials Guide to JavaServer Faces View Definition Framework: [URL] ....
how is the variable passed to the file? Once it's passed, how is it referenced?
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Dec 13, 2014
so i followed a tutorial on youtube called "Java Game Development with Slick" - by thenewboston,URL....okay, so i have made my game / program, and now i just want to export it to a jar file that people can double click and play..unfortunately when i double click the .jar file nothing happens...i get the little "loading" thingy on my courser but it disappears after about 5 seconds and then nothing happens :(the way i made it into a jar file is by doing the following:
-right clicked my java project..
-clicked on "export"..
-clicked on java / Runnable JAR file
-filled in the stuff, (JARs destination ect..)
-pressed finish..
-then i got a jar file on my desktop and double clicked it....but as i said....nothing happens
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Apr 8, 2014
Since I done a recent git pull on my project, for some reason now Im getting an error when starting Tomcat and rendering the index.jsp, but I dont understand whats changed, as this was working before.
The error:
org.apache.jasper.JasperException: /index.jsp (line: 4, column: 42) File "/blog.postTags" not found
org.apache.jasper.compiler.DefaultErrorHandler.jspError(DefaultErrorHandler.java:42)
org.apache.jasper.compiler.ErrorDispatcher.dispatch(ErrorDispatcher.java:443)
org.apache.jasper.compiler.ErrorDispatcher.jspError(ErrorDispatcher.java:133)
org.apache.jasper.compiler.TagLibraryInfoImpl.<init>(TagLibraryInfoImpl.java:168)
org.apache.jasper.compiler.Parser.parseTaglibDirective(Parser.java:410)
org.apache.jasper.compiler.Parser.parseDirective(Parser.java:475)
org.apache.jasper.compiler.Parser.parseElements(Parser.java:1427)
The index.jsp:
<!DOCTYPE html>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ taglib prefix="p" uri="blog.postTags" %>
<html>
<head><title>Blog Home</title></head>
<body>
<h1>Blog Home</h1>
<br />
<% out.println("Your IP address is " + request.getRemoteAddr()); %>
[code]....
I really am unsure as to why this has stopped working, I even rolled back to an earlier commit and this was definitely working before, but I havent changed anything, Initially when you start Tomcat is shows another error in the browser, but on a refresh its a null on this tag library?
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