Its written that every constructor calls its super class constructor. And we know, constructors are called to create an object. Does it mean that if I am creating an object of a class, I am actually creating objects of all its super class???
View Repliesimport java.util.ArrayList;
public class LectureRoom{
private String courseName;
private String roomNumber;
private String Lecturer;
private ArrayList <Student> studentList;
[Code] .....
Question:
Given the following BlueJ class diagram
Lecturer class (same with previous lab, no changes needed)
Student class (same with previous lab, no changes needed)
LectureRoom (changes occurs here)
1. LectureRoom has roomNumber (e.g. A301), courseName (e.g. Java), lecturer (a reference to a Lecturer object), and studentList (a reference to an ArrayList that stores Student object).
2. LectureRoom has a constructor that receives courseName, roomNumber, and Lecturer. The constructor then sets/assign the courseName, roomNumber and Lecturer. This constructor also creates the studentList arraylist object.
what does super(); do in the following method, I understand its uses to access variables belonging to the superclass but i am unsure of what that one line does. Here is a sample constructor..
public CreditCard()
{
// fill in the default constructor and use the super call
super();
id = "000000";
year = 0;
}
The super keyword when used explicitly in a subclass constructor must be the first statement but what about if i have a this(parameters) statements ? As the this one must also be the first statement... Does this means that i can have only one or the other ? What about when the super constructor is not explicit (aka implicit ) , can i use the this( parameters) in the same constructor ?
View Replies View RelatedI am getting error in second constructor that I have created, it gives an error: cannot find symbol variable
package Objects;
import javax.swing.JOptionPane;
public class Constructor {
public static void main(String[] args) {
Piggybank1 pg1 = new Piggybank1("Abhinav", 500);
pg1.deposit(200);
pg1.withdraw(10);
[Code] ....
I am trying to call a constructor from PrepaidCard class in my main method, but I am not sure how to proceed.
As seen below, both the PrepaidCard constructor and the setCardID method have the ability to set the card ID.
public class PrepaidCard
{
public PrepaidCard(String id, int token) {
cardID = id;
tokenBalance = token;
}
public void setCardID(String id, int token) {
cardID = id;
tokenBalance = token;
}
}
Now in this block of code, I can successfully pass the id and token value by calling the setCardID method from the PrepaidCard class. Now I would like to call the PrepaidCard constructor from the PrepaidCard class to pass the id and token value, instead of using the setCardID method.
public class PrepaidCardTest
{
public static void main(String[] args) {
PrepaidCard card2 = new PrepaidCard(id, token);
System.out.print("Enter Card2 cardID: ");
id = input.nextLine();
card2.setCardID(id, token);
}
}
How to call the PrepaidCard constructor from the PrepaidCard class, to successfully pass the id and token value, in my main method?Specifically how to modify or replace this line of code so that it can correctly call the PrepaidCard constructor?
card2.setCardID(id, token);
I am trying to call a constructor from PrepaidCard class in my main method, but I am not sure how to proceed.
As seen below, both the PrepaidCard constructor and the setCardID method have the ability to set the card ID.
Java Code:
public class PrepaidCard {
public PrepaidCard(String id, int token) {
cardID = id;
tokenBalance = token;
} public void setCardID(String id, int token) {
cardID = id;
tokenBalance = token;
}
} mh_sh_highlight_all('java');
Now in this block of code, I can successfully pass the id and token value by calling the setCardID method from the PrepaidCard class.
Now I would like to call the PrepaidCard constructor from the PrepaidCard class to pass the id and token value, instead of using the setCardID method.
Java Code:
public class PrepaidCardTest {
public static void main(String[] args) {
PrepaidCard card2 = new PrepaidCard(id, token);
System.out.print("Enter Card2 cardID: ");
id = input.nextLine();
card2.setCardID(id, token);
}
} mh_sh_highlight_all('java');
How to call the PrepaidCard constructor from the PrepaidCard class, to successfully pass the id and token value, in my main method?
Specifically how to modify or replace this line of code so that it can correctly call the PrepaidCard constructor?
Java Code: card2.setCardID(id, token); mh_sh_highlight_all('java');
I have login.jsp and home.jsp.
Each have its own servlets.
When I click Login button from login.jsp, it will navigate to home.jsp.
But before displaying home.jsp from he user, I want to call homeServlet.java's constructor/method.
This is because I want to populate a dropdown from home.jsp from a database.
I'm using MVC2 Servlet/JSP/Bean framework and AMAP, I do not want to execute javascripts/jquery for populating dropdowns.
Java Code:
class GenericQueue<E> {
private LinkedList<E> list = new LinkedList<E>();
public void push(E element) {
list.addFirst(element);
}
public E pull() {
return list.removeLast();
[code]...
Is a constructor required to create an object, if one of its instance or class variables haven't been instantiated? Like private String string;
I want to create a simple app that takes a name from the console then compares the name to a small phone book,when the name matches another name it will return the associated phone number.
I have a small contacts class which has name and number fields,Then I have a phone book class which populates an array with 4 contact objects that I can compare the entered number against.
here is my contacts class
public class Contact
{
String name;
int number;
[Code].....
In the main method I am just trying to print out one of the fields for one contact to see if I can actually access it to compare it to the name entered.Its saying "MaryJones" cannot be resolved to a type.I'm guessing I cant create all that code in the constructor?
The requirements are as follows:Design and implement the class Day that implements the day of the week in a program. The class Day should store the day, such as Sun for Sunday. The program should be able to perform the following operations on an object of type Day:
A. Set the day.
B. Print the day.
C. Return the day.
D. Return the next day.
E. Return the previous day.
F. Calculate and return the day by adding certain days to the current day. For example, if the current day is Monday and we add four days, the day to be returned is Friday. Similarly, if today is Tuesday and we add 13 days, the day to be returned is Monday.
G. Add the appropriate constructors.
H. Write the definitions of the methods to implement the operations for the class Day, as defined in A through G.
I. Write a program to test various operations on the class Day.Should I break down my day.java into several separate classes, one for each of the sections (previous, next, etc)?
import java.util.*;
public class MyDay
{
static Scanner readinput = new Scanner(System.in);
String day;
public MyDay(String day)
{
day = "Sunday";
[code]....
Ideally I would like to create a Gui that would have someone type in the day, and then press a button to return the next day, prior day, or have a text input to test for adding X number of days.
I thought you can only create a new object using private implementations and then using a constructor to set your arguments inside the parameters of the constructor to the instance variables but how come he created an object without any private implementations and just methods inside the constructor.
import javax.swing.JFrame;
public class MyWindow extends JFrame {
public static void main(String[]args){
new MyWindow();
}
public MyWindow(){
setSize(500,500);
setVisible(true);
setTitle("MyWindow");
}
}
I have two classes LightController & Circle. I need to use the LightController class to do the following:
Creates an instance of Circle with a diameter of 50 and a colour of OUColour.GREEN and assigns this new circle to the instance variable light.
Sets the xPos of light to 122.
Sets the yPos of light to 162.
I am struggling to write the correct line of code to set the colour to green and set diameter to 50.
Code for the two classes below.
001
import ou.*;
002
import java.util.*;
003
/**
004
* Class LightController
005
* This class uses the Circle class, and the Shapes window
[Code] ......
Will the code below just create a new blank window rather than call the one I have? I want to call the one I have from my main method ideally.
JMenuItem menuDelete = new JMenuItem("Delete");
menuDelete.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
DeleteEnvironmentWindow deleteEnv = new DeleteEnvironmentWindow();
deleteEnv.setVisible(true);
}
Instructions
Create a WordCounter class with a constructor that takes a file name as a parameter
The class should have two fields: one for the file name and one for a HashMap to store word count information
The constructor should call a private method, countWords, that reads in the file and counts the word frequencies
The class should contain a get method for each field, as well as a print method that prints out the map in the following format:word:frequency
When printing, the map should be sorted by either the word order or frequency (Hint: see Collections.sort)
You should include the sample text file on Blackboard. This is what i got so far
Java Code:
import java.io.File;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.Scanner;
public class WordCounter
[Code] ....
public Unit(String code, String name)
{
enrolStudent(student);
this.unitCode = code;
this.unitName = name;
}
public void enrolStudent(Student newStudent){
students = new ArrayList<Student>();
newStudent = new Student(24662496, "Kingsley", " Iwunze");
students.add(newStudent);
}
how can I call this enrolStudent() method on this Unit constructor in another class when I create a new Unit. all I need is to enroll students in units when units are created. below is my create unit method.
public void createUnits( ){
units = new ArrayList<Unit>();
units.add(new Unit("FIT2034", "Java Programming 2"));
units.add(new Unit("FIT2024", "Software Engineering"));
units.add(new Unit("MAT1830","Discrete Maths"));
unit.enrolStudent(new Student(25486321, "Julia", "Garcia"));
unit.enrolStudent(new Student(44589736, "James", "Olivia"));
unit.enrolStudent(new Student(47852103, "Lucky", "Thyriod"));
}
When using Java Code:
Scanner scan = new Scanner(system.in) mh_sh_highlight_all('java');
Why do we put System.in in the constructor? What purpose does it serve and why can't we just not use it?
that i started to learn programming and i started with java. so there is a book that i'm on it right now called "Pearson Absolute Java 5th Edition" by Walter Savitch anyway i'm on a project in fifth season which i have to create a class named HotDogStand that operates several hotdog stands distributed throughout town. the whole program is clear. although its so easy to accomplish , my question is more about debugging. so here is the code:
public class HotDogStand
{
private int id; //id number of hotdog stand
private int hotDogsPerDay; //hotdogs sold by one stand
private static int totalHotDogs; //the static value for total hotdogs sold by all the stands
public HotDogStand (int newID, int hotDogsPerDay) {
this.id = newID;
this.hotDogsPerDay = hotDogsPerDay;
totalHotDogs += hotDogsPerDay; //to add the value every time the user uses the constructor (every time the user creates an object)
[code]....
everything works fine. but my question is what if someone use a constructor again? you see if in the main method someone do this after creating the object "stand3":
HotDogStand stand3 = new HotDogStand(3, 43);
stand3 = new HotDogStand(3,40);
i know that it's logical to use setter method but this program doesn't have one. if someone do the thing i wrote above, the calculation of static variable, totalHotDogs will be all wrong. because of totalHotDogs += hotDogsPerDay; it will add another value for the same object. how can i tell the machine to ignore the second (or more) invocation of the constructor for the same object?
I want to create an order system. My Problem is that I want to create it dynamic, with ArrayLists and no fixed Array size.
Basically I have already a User which is able to purchase something.
User a = new User();
Car car = new Car("blue",500);
a.purchase(new Order(new OrderThing(5,car));
This will work!
But I want something like this:
a.purchase(new Order(new orderThing(5,car), new orderThing(2,car), new OrderThing(1,car),...)
Basically I don't know how much OrderThings I want to create before I type in the OrderThings with new Order().
But in java it is before you can construct orderThings you must already know in the constructer how much objects you do want.
Now as im writing this question I got a idea of waiting for an Array of new OrderThing but it don't work. When I write
a.purchase(new Order(new orderThing(5,car), new orderThing(2,car)))
it wants a constructor which is based on Order(orderThing,orderThing)
So I want to write a constructor that creates a new object with the data from the array values. I don't know where to start. It's the last method in the code:
public class Measurements {
private double[] values;
private double[] newArray;
private int n; //numberofvalues
private double[] ms;
public Measurements(int max) { //constructor
[code]....
I have a class of Date with a constructor with 3 parameters in it. Those 3 parameters are int data type just to enter month, year, day.
I have another class called Author which has a constructor of Date diedDate; as a parameter passing to the Author constructor.
I was asked to call the Date parameter is null, call the default constructor but I thought for the Date parameter I could only enter something like 0,0,0 instead of typing in null, null, null because null is for String data type isn't it?
what have I done wrong n the following code? I'm trying to create a new instance carte of object Carti using the constructor and then to insert a row into a table created with SQL.The error I'm getting is:
Exception in thread "main" java.lang.NullPointerException
at Carti.Carti.InsertCarti(Carti.java:103)
at Main.main(Main.java:37)
Java Result: 1
BUILD SUCCESSFUL (total time: 28 seconds)
The line Main.main(Main.java:37) is when I try to insert the row.
The line Carti.Carti.InsertCarti(Carti.java:103) is when I do the
PreparedStatement st = conn.prepareStatement("insert into Carti (Id,titlu"
+ ", descriere, autor, editie, anPublicare) values (?,?,?,?,?,?)");
Here is the code (Main and Carti Classes)
import Carti.Carti;
import Imprumut_Carti.Imprumut_Carti;
import Membrii.Membrii;
import static com.sun.org.apache.xalan.internal.lib.ExsltDatetime.date;
import static com.sun.org.apache.xalan.internal.lib.ExsltDatetime.date;
import java.sql.SQLException;
import java.text.DateFormat;
[code]....
I've a parent class with a argument constructor like below(a sample code)
public class Parent {
Parent(String name) {
System.out.println(name);
}
public static void main(String[] args) {
}
}
Also I've child.class which extends Parent.class as shown below,
public class child extends Parent {
child(String name) {
super(name);
}
}
Now, I want create/modify the constructor which is in child, by taking "int i" as an input instead of "String name". How can I do that? Run time I want to execute child constructor not a parent constructor.
Condition is: Without making any changes to the Parent class
I'm really new to object oriented coding. A good way to create a Text Based Game that used objects as rooms, and items. However, I can't figure out what the best way to define and use rooms and items would be. I've been at it for the past few days, and just can't think of something that works well and is easy to use.
I want to have each room have it's own "inventory" of items that the player can pickup, as well as drop items into. I want items that are dropped to maintain their properties (durability, level, ect). I would also need several methods for things like getting an item from a room by the item's display name or id. For instance, if there is a room with a Broken Iron Sword, and a Stone Dagger, I'd need to be able to get the Broken Iron Sword object with the string "Broken Iron Sword".
package home;
import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class Box{
int x=70;
int y=70;
[Code] ....
L a = new L(); causing the error. It will be great to know why it is showing error.
I just want to ask about a kind inheritance.Let say I have an interface MachineCode.I also have different classes, Binary, Hex and Octal that implements MachineCode
Question: How can I prevent java to create an Object like this:
Binary bin = new Binary();
Hex hex = new Hex();
Octal octal = new Octal();
those declaration above must be compile error,
I want to create Objects of Binary, Hex, and Octal this way:
MachineCode bin = new Binary();
MachineCode hex = new Hex();
MachineCode octal = new Octal();