Understanding Classes And Objects In Terms Of Data Types
May 8, 2015
I have seen many ways of describing what objects are, one being that objects are a user-defined datatype. However, if objects are datatypes, then what does that make classes? To me, it seems as though classes should be the "types" of data defined by the programmer, and objects should be the specific "values" of that user defined data type. As an example, an integer would be a class, while 1 would be a "value" of that class, i.e. an object. From this point of view, I don't see why a specific number would be a data type... Therefore, why do we say that objects are user defined data types rather than classes?
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Apr 29, 2014
I'm making a program that displays information for "employee" objects of different types. This works with a hierarchy that goes Person→ Employee→ Fulltime/Adjunct, and a driver that tests the inheritance. The Person class is given and only supplies the name, the employee class manages the year hired and the ID, and the types of employee classes manage the salaries.
One object (called staff[2]) is supposed to first be printed with default information and then later updated via set methods. I figured out how to update the name, but I don't know how to update the rest of the information because the employee's name is managed in the Person class and the reset of the information is managed in the less-general classes, and the objects are all in an array of Person.
How do I call the set methods necessary to update more of staff[2]?Output (scroll to see the updating section)
The current year is 2012
Name: Flintstone, Fred
ID Num: BR-1
Year Hired: 2005
Years Of Service: 7
Salary: 65000.12
Fulltime Type Employee
[code]....
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Oct 6, 2014
I have written several simple data classes that I serialized manually by converting to text. At this point I need to serialize a more complex data structure. which will include lists of the simpler elements. Can serialize store and reconstitute this type of structure automatically or do I need to do this one manually as well? Consider the pseudocode below for a clarification of my question;
Java Code:
Class Hops{
String Name;
float Alpha Acid;
float Beta Acid;
};
Class Malt{
String Name;
float extract;
};
Class Recipie{
String Name;
CList HopList;
CList MaltList;
};
CList RecipieList; mh_sh_highlight_all('java');
I read the article on Serialization presented at tutorial point, but the example only showed a simple class, not lists of class members. What I want to do is serialize RecipieList, which consists of a CList of Recipies, which in turn consist of CLists of various ingredients.
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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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Jul 27, 2014
I am currently working on a project where I need to return data from a database over RMI to a client who requests it. Some of the fields in the Data Object can not be seen by the client so I need to create another object to send over the network instead. The method I use is this...
public static SerializableObject createSerializableObjectFromDataObject(DataObject dataObject){
SerializableObject serializableObject = new SerializableObject();
serializableObject.setField(dataObject.getField());
serializableObject.setAnotherField(dataObject.getAnotherField());
return serializableObject;
}
Is there a better way of doing this? I am creating many subclasses DataObject which all require this static method to be implemented and I can't push it into the superclass because each one needs custom behaviour.
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Jun 13, 2014
I know that static method cannot use non-static methods .Then how the following code works ,where main method is static and this main method calls go() method which is a non-static method .
import javax.swing.*;
import java.awt.event.*;
public class SimpleGuib implements ActionListener {
JButton button;
public static void main(String[] args) {
SimpleGuib gui = new SimpleGuib() ;
gui.go() ;
[code]....
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Jun 12, 2014
I recently had to work on a very simple banking application. Since customers provide their account numbers when they go to the teller to perform a transaction, I chose account number as the key to uniquely identify a customer. To address the fact that a customer can have multiple accounts, I decided to have an entry for every account the customer had, as part of my Teller class, so that he can identify himself with any of his active account numbers. When I was discussing this design with my friend, he felt it was bad and that I had to have a CustomerID field to uniquely identify a customer. I can't seem to understand why we can't do that with account numbers belonging to the customer?
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Jun 5, 2014
I have an int array that has information read from a file. Now i want to display this int on a jtable but ofcourse i cant display primitive data types.. and also you cannot cast an int[] to an Object[], so I am stuck...
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Nov 16, 2014
I have declared an array list that will store data type of 1 Character and 2 integer. The data that will be store in this list is
1. A = {0 3}
2. B = {0 5}
3. C = {0 3}
4. D = {0 3}
5. E = {0 5}
6. F = {0 6}
Now here the alphabets are routers and integers are there con1 and con2 respectively. I have a set of router={ A,B,C,D,E,F}.
Step 1:I have to subtract con1 from con2 i.e. (3-0) of all the routers and
Step 2: then put the router having largest value in new set 1 and
Step 3: then this router will be subtract from the router set.
Step 4:then again I have to repeat the step 1 until the value of routers become <= 1.
Now what I did is I defined 3 arrays first is String array that stores names of routers, 2nd array that stores the first value and 3rd array that stores the second value. I can find the largest value but how to store the name of router against the largest value in the set.
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Feb 14, 2015
For class, we need to create a word game using classes and objects.
The game is played in rounds. The player is presented with a word that is missing letters. The player has to fill in the missing spaces with their letter guesses. The words presented are chosen with a random number generator which has been provided for us. At the end of the game, the player is shown their score.
In steps, I have to:
-Welcome the player.
-Present the puzzle.
-Allow the player to fill in the blanks.
-Have the program check responses for correct/incorrect input.
-End the game if they have three misses, or continue if they complete the puzzle.
Now, to start, I have a class for the number generator, a class to store the array of 25 words, and a class for the game itself.
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Sep 7, 2014
I need to write a simple program that displays up to 5 pairings of data types (int, string) (string, long) ect. I need to have at least two classes, a Pair class (generic) and an PairTest class.
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Oct 12, 2014
I have to read data from a text file and print it in a new text file. An example of one line is like this:
Johnson 85 98 75 89 82
I then have to take the average of all the numbers and assign a "grade" to the numbers for each line of the text file and make a new file so it looks like this for 10 lines:
Name 1 2 3 4 5 Average Grade
Johnson 85 98 75 89 82 85.80 B
My problem is extracting the data from the file so I can use it.
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Jun 29, 2014
Trying to find a way to use primitive data types to overload sound()method. I can't seem to warp my head around using an int or a double to overload the method. And if I did, how do you call them in the main afterwards?
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Mar 15, 2015
The question states: Design a class named LinearEquation
for a 2 x 2 system of linear equations:
ax + by = e
cx + dy = f
Where
x =
ed − bf/ad − bc
y =
af − ec/ad − bc
The class contains:
- Private data fields a, b, c, d, e, and f.
- A constructor with the arguments for a, b, c, d, e, and f.
- Six get methods for a, b, c, d, e, and f.
- A method named isSolvable() that returns true if ad−bc is not 0.
- Methods getX() and getY() that return the solution for the equation.
Write a test program that prompts the user to enter a, b, c, d, e, and f and displays the result. If ad − bc is 0, report that "The equation has no solution."
I believe that my program is correct because I am able to compile it and get no errors, however I have no clue how to display the information for x and y or display this equation has no solution if ad-bc=0.
Java Code:
import java.util.Scanner;
public class Exer911 {
public static void main(String[] args){
// Create a scanner system to hold the numbers for each variable
Scanner input = new Scanner(System.in);
// Prompt the user to enter a number for each of the variables
[Code] ....
How to get the information to display ....
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Aug 6, 2014
How I'm supposed to write out the statement.
I am fairly certain that I should be making variable "b" and "c" a float. But beyond that I'm confused.
uploadfromtaptalk1407333378833.jpg
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Sep 13, 2014
I get an error when I try to divide 500 miles by 25.5 gallons
Exception in thread "main" java.lang.NumberFormatException: For input string: "25.5"
at java.lang.NumberFormatException.forInputString(Num berFormatException.java:65)
at java.lang.Integer.parseInt(Integer.java:580)
at java.lang.Integer.parseInt(Integer.java:615)
at Mileage.main(Mileage.java:42)
Java Result: 1
[Code] .....
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Aug 25, 2014
I would like to create an ArrayList from data types stored in a text file.The ArrayList would be multidimensional with two data types; int, String.
Example text file could be:
4 cahiers grand format
3 stylots bic bleu
5 gommes
I find it very difficult for multiple data types i don't see how its possible.
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Sep 1, 2014
I am trying to remove the duplicate elements from ArrayList using .contains() if elements are primitive datatype it works but user-defined datatype does not work.
public class UserBean {
String name;
String address;
public String getName() {
return name;
[code]....
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Jan 17, 2015
I am creating a calculator in which a user will directly input the numbers and the operator...
Here is my code:
int answer = 0;
int num1, num2;
char operator;
System.out.print("Enter calculation: ");
num1 = kb.nextInt();
operator = kb.next().charAt(0);
num2 = kb.nextInt();
The code above will accept the user input when there are spaces like this: 1 + 1
So the program will give an answer which is 2...BUT
if i input 1+1 it will give an error...Exception in thread "main" java.util.InputMismatchException
How can i do that it will separate integer to character? because i set the operator as character....
So that it will accept one digit to several digit numbers... like 500+84 or 1520+872??
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Nov 29, 2014
If I lets say have an interface Animal, and I create a lot of classes with a different animal name that implement the interface Animal. Then I create an ArrayList of Animal. Then I would put in lets say Dog class into the ArrayList, which has custom methods and data that the Animal Interface doesn't have, is this data ripped away except for the methods that are put in the Animal interface? So if I would cast the Animal back to Dog, would it retain all the data that existed before it was placed in the ArrayList?
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Jan 22, 2014
What I'm doing about it: googling the shit out of my problems, consulting you fine readers, consulting my friends, and yesterday I signed up for Lynda.com. I'm hoping 30hrs+ or so of watching, rewatching, and analyzing the example code will catch me up before I get too behind in CS302
** Assignment Prompt **
Integer types are very convenient, but their limited width and precision makes them unsuitable for some applications where precision is more important than speed. Develop a class VeryLargeInteger that can handle arbitrary long integer numbers (both negative and positive) and the basic arith- metic operations (addition, subtraction, multiplication, division, and remainder).
Hint: The number could be represented as string, the sign could be represented either as boolean or as part of the string.
Note: Implementations of addition/subtraction through repeated use of a constant incremen- t/decrement will not be accepted. Implementations of multiplication and division that rely only on addition and subtraction will not be accepted.
I know I'm going to have to create a separate tester to call on the VeryLargeInteger class and it's math methods. For the new data type, should I convert the integer/string into an array in order to handle the large length of the number? I know he wants us to use recursion for the math methods. My gut tells me addition and subtraction will be slightly easier than multiplication and division. I know I'll have to reference the other methods for division. We aren't allowed to use the BigInteger class.
How I should construct any of the methods.
Java Code:
import java.util.ArrayList;
/**
∗ VeryLargeInteger (VLI) is a class for arbitrary precision integer computation
*/
public class VeryLargeInteger {
private int[] num1;
private int[] num2;
private int[] num3;
[code]....
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Nov 12, 2014
I have a problem with this ascii animation program I am working on. I declared a method inside of my class AsciiAnimation extends JFrame implements ActionListener, called
package AsciiAnimation;
import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;
import javax.swing.*;
public class AsciiAnimation extends JFrame implements ActionListener{
int currentFrame = 0;
ArrayList<String> frameList = new ArrayList<String>();
[Code] ....
Basically I just am trying to figure out how java works with me accessing those 2 data members, currentFrame and frameList inside of my first class ALL in the same package.
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Mar 7, 2015
I have a class which connects with database and fills object with data. Method looks like this:
//in database class
void getData(anObject a, int id){
//connects with database
a.field1=get...
a.field2=get...
....
//disconnects
}
Now I want to use this method in anObject class, but I can't call it because I don't have created object jet. Is there any way to call this method?
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Oct 3, 2014
I've been unable to figure out how to access an objects data from another class. I ended up missing a lesson in java and haven't been able to catch up on this topic on my own through my textbook.
Error: has private access
Code:
public class TestCoffeeDrinker {
public static void main(String[] args) {
Coffee latte = new Coffee("Starbucks Tall Latte", 2.85);
Coffee mocha = new Coffee("Starbucks Grande Mocha", 3.95);
Coffee mcdonalds = new Coffee("McDonalds McCafe", 0.99);
System.out.println(mcdonalds.toString());
[Code]...
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Apr 23, 2014
I want to keep count of how many students are in my array. the array i made up of objects from other classes. like the class Student how do i do this. i have tried contains but better way it to to a loop to go through the array and determine if each object is a particular type but i don't know how to do this. here is the code
import java.util.*;
import java.util.ArrayList;
public class Driver {
public static void main(String[] args){
/* Comments required
PersonFileReader pfr = new PersonFileReader("person.dat");
ArrayList<Person> testData = pfr.readData();
Database db = new Database(testData);
[Code] .....
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Apr 29, 2014
How do we cache objects in EJB 2.
My requirement is i need to get data from the database for the first time and retain in cache it throughout the application life.
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