Reference Variable - Create Another Variable And Set It Equal To First
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.
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.
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">
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`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?
I am trying to simplify my constructor by using "this" reference variable. I am aware how to use this reference when making constructors that involve fields of primitive data types; however, not so sure fields involving objects. I have made the following constructors and haver placed a question mark in the last parameter. How I can use this reference that involves objects.
public class RetailItem { //Create the fiels for item. //You need item name and item number. then you would need //cost private String description; private int Item_Number; private CostData cost;
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?
I don't understand why the object reference variable 'a' cannot be recast from a thisA object reference to a thisB object reference.Is it the case that once a reference variable is linked to a particular object type then it cannot switch object types later on.I am facing the Java Associate Developer exam soon and I am just clearing up some issues in my head around object reference variable assignment,
class thisA {} class thisB extends thisA { String testString = "test";} public class CastQuestion2 { public static void main(String[] args) { thisA a = new thisA(); thisB b = new thisB();
Okay, so I know how to get user input and create a variable from the input, create a basic addition sum etc...
So I have this code:
package calc; import java.util.Scanner; class calc{ private static final double add = 0; private static final double subtract = 0; public static void main(String args[]){
[Code] .....
I'm basically trying to make it so that when the user enters tnum, tnum2, tnum3 and tnum4, their answer turns to the variable which has to be either true or false to make the boolean work. I don't know really how to do this. I want to make it so that if they enter yes, then that makes the boolean true and the numbers will multiply and create the answer variable. If they enter no then the boolean is false and it moves onto the next if statement. How can I do this?
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?
I have searched for totalPay is always 0 and the responses are not related to my problem (that I can tell).This is a class assignment and I have other questions besides why the method is not working.
Here are the instructions: Create class Employee which contains a String variable Employee Number, a String variable Employee Name, an integer Hours Worked, and a double Pay Rate. Create get and set methods for each variable. Provide method "totalPay" which calculates and returns the total pay by multiplying the hours worked by pay rate. Use figure 8.12 as an example of an object with get and set methods.
Unlike other examples of this type question online this one has Employee Number as a String variable. The book is How to Program Early Objects by Deitel 9th edition.We have instructions to do only what she has told us too. At this point it is objects and getter and setter methods. It is only the beginning of week 2.
ON THE LINES WHERE I HAVE QUESTIONS I AM COMMENTING IN ALL CAPS. NOT SHOUTING, JUST TRYING TO MAKE IT EASIER
package test11; import java.util.Scanner; public class Test11 { public static void main(String[] args) { Scanner input = new Scanner(System.in);
[code]..
Essentially I cannot figure out how to get the method getTotalPay to be called by the Scanner and do the math. I also have this random bracket problem that showed up about an hour ago.
The concept I don't get is that if I omit this.employeeNumber =id; etc. I error all over the place. If I change it to this.employeeeNumber = employee Number Netbeans tells me it is assigning itself to itself, which I know. When I try to use id instead of employeeNumber I get errors all over. If i remove "this" from it the same happens. why in public class employee I have to change to those values (id, name, etc) in the construct and set them again? I don't see where or how they can be used, so why do i have to do it?
I'm suppose to create a program that will check if one statement is equal to another but it doesnt display the message if its equal to the inputted String
import java.util.Scanner;
public class sup { public static void main (String args[]) { Scanner in = new Scanner (System.in); String one;
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thats just an example I was able to do it in C++ but it doesnt do what I want in Java
I'm trying to design a website that will require users to register and login before they use it. In order to keep things separate, I was thinking it might be useful to create a single web archive that just handles the user signup and login. That way I could work on my other web archive apps independently and have them just check to see if the user has logged in and posted a token somewhere, and if not redirect to the login webpage.
How do I use a variable in an if statement to return a public void method from another class? I've tried:
System.out.print("select 1 - 6: "); Scanner myScanner = new Scanner(System.in); myScanner.nextInt(); if (myScanner.nextInt()==1) { carSelection colour = new carSelection(); colour.carSelection();
The method colour in class car selection is just 4 print line statements? I've // out the if statement to see if it is correctly calling the method and displaying the data and it is?
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)
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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;
i have a datatable with id= tblId#{emp.id} <c:set var="tableID" value="tblId#{emp.id}"> displaying employee details inside c:forEach closing dataTable.
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For ex.Displaying 5 table dynamically.Need to validate check box selected or not.5 table are displayed.But it shows 5th table row id only.It is because of local varible declaration?
I'm making a program where the user enters an ID number and can submit the amount of sales that person made for a specific product and write to a file. One of the things I have to do is making a running sum of the sales for each product for all people combined as well as an accumulation of the a persons sales every time he enters data. Everything seems to be working execpt my values like person1Total, person2Total...etx and product2Total.
When I try to write them to the file, they always come out at 0.0 even though they should be the sum of the indexes of the array sales.
I'm working on a program where the user inputs song information (name, artist, filesize, duration) which is stored in a database. Once the user adds a song, the details should be stored in the first empty song slot (4 song slots total) and then taken back to the menu interface.
What I'm having trouble with is that I can add the first song fine (song1), but when I try to add another song, the information entered into song1 is gone. I've worked out that this is because every time I call upon the addNewSong() method, I'm creating four Song objects that are brand new with the line:
Song song1 = new Song(); Song song2 = new Song(); Song song3 = new Song(); Song song4 = new Song();
How to fix this problem is where I'm stuck because if I move these lines elsewhere, I get a 'cannot find symbol - variable song1' error.
Here is my code:
public class SongDatabase { Scanner console = new Scanner(System.in); public void addNewSong() { Song song1 = new Song(); Song song2 = new Song(); Song song3 = new Song(); Song song4 = new Song(); if (song1.isEmpty()) {
I trying to display the value of a variable from a method, but I don't know why it will I can't do it.
//Java extension package import javax.swing.JOptionPane; public class Palindrome { public static void main(String[] args) { int number = 0; int palindrome = 0;
I have code that displays 3 game scores the series total and average. For some reason game 3 outputs 0 and game 1 and 2 output correctly. I don't see anything different that game 3 is doing that game 1 and game 2 aren't so I'm not sure what the problem is.
java file
package com.valenciaprogrammers.mybowlingscores; import java.text.DateFormat; import java.util.ArrayList; import java.util.Collections; import java.util.Date; public class BowlingScores implements Comparable<BowlingScores>{ private long id;
I have a problem with my code. When, on strausParser class, i create the new object Beam i give him an array of Node object called "nodiestremi".
The problem is that when a Beam is created, the Beam created before take the Node of new Beam. Why it appends?
public class Main { public static void main(String[] args) throws NumberFormatException, IOException{ SetFile.setupWindows(); Structure structure = new Structure(); } public class SetFile { }
My code has a method where the users input a bunch of variables and then those variables get added together in a new variable. What I want to know is how do I call the variable that is in the other method to another method?
import java.util.*; public class Calc{ public static void main (String [] args){ determinevalue1(); determinevalue2(); determineTotalvalue(double value1, double value2);
I have a class Tree in which all the methods to build a tree are in place. But however I would want variable of by Tree which is pointing to the last node being added to the tree.
So basically every time you keep adding a node to the tree you tail pointer gets updated to point to the last node. I have this so far.
public class NonEmptyTree implements Tree { private Tree left; private int data; private int leftleafCount; private int rightleafCount; private Tree right; private Tree tail; // This variable must be shared by all the object. There needs to just one tail pointer to the tree. public Tree insert( data ) { tail = // gets updated every time when new node gets added.
I am going through Thinking in Java, 4th Ed and I came across the section that talks about overloading variable arguments. I tried out a piece of code from the book. (Method and class names not exactly the same).
public class Varargs { public static void m1(Character... args) { System.out.println("Character");
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In the above code, the compiler throws an 'Ambiguous for the type varargs' error. The error goes away if the first method is changed to:
public static void m1(char c, Character... args)
why there is ambiguity in the first piece of code and not the second.
