Create A New Instance Carte Of Object Carti Using Constructor
Mar 30, 2014
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 (?,?,?,?,?,?)");
I can't figure out where to create the StringHandler object. My code should take a string as input, then create StringHandler object ord with the string input. This should repeat until cancel is pressed, then ord should be sent to the Utskrift-method (a print method).
If I do like this, null is also sent to Utskrift. I dont want that to happen. If I put StringHandler last in the loop ord can not be resolved.
String text = ""; while (text != null){ text = showInputDialog(null, "Enter text:"); StringHandler ord = new StringHandler(text); if (text == null){ [Utskrift(ord.getNumber(), ord.getString(), ord.getWords()); break; } }
public void randomCreate(ParentObject obj){ int x = random(0-4); //pseudo int y = random(0-4); //pseudo create new ParentObj(x,y); }
ParentObject is actually abstract, so you would only ever pass one of its children objects to it, and a child object of that type would be created. It seems like there should be a way to pass a type, rather than an object, and then create an instance later down, but I don't know if that is actually possible, or if it is poor programming style.
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?
.I was reading head first java book and saw a barbell question on page no. 280,question-"what if you want to write a class in such a way that only one instance of it can be created,and anyone who wants to use an instance of the class will always use that one,single instance?"
I have been working on a program that is meant to use a class' instructions in a program to add a value to a variable, save it, and present it. This is my class
public class Car { //FIELDS private int yearModel; private String make; private int speed; //METHODS public Car(int carYearModel, String carMake)
[Code] .....
Whenever I call the accelerate method, a value of 5 is to be added to the speed variable. But whenever I call accelerate, it doesn't increase! I just don't understand why not. I've tried different renditions of adding 5 to speed and it doesn't quite work. I don't get any errors when I compile, just runtime, when it doesn't add 5 to speed.
So far in my assignment I have successfully opened a text file. However I am required to do more:
1) As each line of text (containing names and ages) is read a new Runner object is created with its instance variables set thus: ! (Runner class already created )!
- name : set directly set from the value in the file - agaGroup : can be worked out from the given ages: < 18 should be 'junior' > 55 should be 'senior' the rest should be 'standard'
2) the instance of Runner should be added to the list referenced by the instance variable runners.
I have used if statements to create the junior list, however I do not see the full list of names and ages in the variable runners as I am requested to.
I am sure there is a for loop involved somewhere but I do not know how to:
a) use the for loop in my method add a new Runner object with the variable mentioned.
I include the code I have done so far as a file - p.s I use Bluej.
public class MarathonAdmin { // instance variables private String runners; private String age;
Let's pretend I'm working on an RPG. Like in all RPGs, there are items found all throughout the imaginary world. Each player and NPC can obtain an item. My question will concern those items.
In other words, I'd like to use instances of a class in multiple places of the code. Each instance will have its own, individual values of instance variables, with one obvious exception: itemQuantity should have a different value in playerInventory, npcInventory, etc. Also, I'd like a list of all items that can be found in the game. This list doesn't need itemQuantity at all.
class Items { String itemName; float itemWeight; int itemQuantity;
[Code] ....
The question is: should I really make itemQuantity an instance variable of the Item class? It seems as though for each copy of the Item class I should create a separate copy with different value of itemQuantity, but that's not very efficient. Where is the error in my logic?
What's important is that there may be plenty items in a game and a player may be given power to create new items during the course of the game.
so, i was reading my java book and learning about objects and methods and it starts talking about Encapsulation and mentions that it's good practice to set instance variables as private and instead of accessing the instance variables directly, we should create a set method and get method to get and set the stuff we want to pass to the class containing the object...
for example, in this class, we're passing the integer 70 for object dog one and integer 8 for object dog two for the dog class... and these these 2 integers are sent to the setsize method so we're not accessing instance variable size directly.
i dont quite get it though....if we the programmer are the one deciding what size the integer is for the dog, and the setsize method takes the one.setSize(70) or (8) and puts them in setsize(int s) as s... but only to copy that integer stored in s back to private int size.... why do we even need to bother with making these two extra methods such as setSize, getSize?
in the book it says that... well what if the code gets into the wrong hand and someone writes something like one.setSize(0) then you would get a dog with size 0 which is essentially illogical. but then again, i'm the programmer, and i am the person who writes the code and passing the right integer.The reason for public and private... that part i understand... i can see why if a variable's data can get changed amidst the code during calculations and you dont want it to directly change the original variable and have it mess up the code, but this code from the book just a bad example of demonstrating the reason? since we manually pass the information ourselves and passing it to method setSize... and all setSize does is stores it in another integer, only to copy it right away to size (which is the original private variable we were tryign to protect?
Any simple code to demonstrate how the code might end up changing an instance variable and why we would want to protect it by using private?
class GoodDog { private int size; public int getSize() { return size; } public void setSize(int s) { size = s;
I am currently trying to use Junit to test a whole bunch of stuff. I almost have full line coverage but I am getting hung up on testing an if statement that consists of whether or not an object is an instance of another class. This class happens to be an interface, and even the object is an interface. Weird I know but I just want to know how to get into that if statement. I realize testing interfaces might be a waste of time but I still really want to know how. Here is an example of what I am trying to test:
Java Code:
if(x instance of y){ //where x and y are both interface objects doSomething(); } mh_sh_highlight_all('java');
So in the code below I create an instance of my own triangle class and use one of its methods. The thing is I use one of my triangle classes methods in a method other the main method of my main program so I'm thinking it can't access it?
Any way here's the code for my triangle class
import java.util.Scanner; public class QudratullahMommandi_Triangle_06 { Scanner keyboard = new Scanner(System.in); private double side1; private double side2; private double side3;
[Code] ....
and here's the error message
QudratullahMommandi_S_06.java:46: error: cannot find symbol { triangle1.outPut(); ^ symbol: variable triangle1 location: class QudratullahMommandi_S_06 1 error
Whenever i perform any operation in my application Live Bytes of a particular Instance of a class increases by 1000.Although i perform the same operation everytime it always increases by 100 or 1000.Is this a memory leak or does these instances increase everytime we perform an operation.
Create a class called Employee that includes three pieces of information as instance variables:
-Employee ID (string type) -first name (string type) (default value 'John') -last name (string type) (default value 'Smith') and -monthly salary (type double). -No argument constructor that initializes the three instance variables. The employee id should be generated using the following process:
The employee id should be a combination of first initial, last initial and a number starting from 10001 for the first employee and increasing by one for each employee. e.g. if John Smith is the first employee then its id will be JS10001 and if George Brown is the second employee then its id will be GB10002
-Provide get and set methods for each instance variable. The set method for monthly salary should ensure that its value remains positive - if an attempt is made to assign a negative value, leave the original value.
New to Java Swing. What I am trying to achieve here is to create an instance of the class used to populate the DefaultListModel when a JList item is selected. All examples I have seen show how to return the text displayed in the JList which really is of no practical use.
I have achieved what I want to achieve in that I am successfuly creating the selected object within my ListCellRenderer class.
For the purpose of testing I am using a call to the JOptionPane.showMessageDialog method to display the id of the selected object.
So, I launch the JFrame, the JList is populated, I select an item from the JList and the id value is displayed in the prompt. All this works fine except for one thing.
When I click OK on the JOptionPane.showMessageDialog prompt, the prompt disappears and reappears. The system seems to be in a loop. It is behaving as if the change or click event handler on the JList keeps firing.
This happens even without the creation of the object:
BookEntry be = (BookEntry)list.getModel().getElementAt(list.getSelectedIndex());
I have scoured the code and object properties to see if I can figure out where this behaviour is coming from without success.
All there is in the JFrame design view is a single JList with a variable name of "list". Everything else is in code as below:
Here is the .java code. Its not that complex
import java.awt.Color; import java.awt.Component; import javax.swing.JLabel; import javax.swing.JList; import javax.swing.JOptionPane; import javax.swing.ListCellRenderer; import javax.swing.DefaultListModel; public class NewJFrame3 extends javax.swing.JFrame {
I have to make two classes. The first one crates an instance of an array of several integers and prints data (average, greatest, lowest, et cetera) based on the second class, which contains the methods. I'm having a problem with the syntax for the first class required to use the methods.
Here's a shortened version of what I have right now just based on processing the number of integers in the array (because if I can get just one method properly connected, I could figure out everything else).
Driver
import java.util.Arrays; public class ArrayMethodsDriver { //Creates the ArrayMethods object public static void main(String[] args) { int[] a = {7,8,8,3,4,9,8,7};
[Code] ....
When I try to compile this, I currently get the "class expected" error on the count part.
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?
import 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.
Task:The main method of the class Things below creates an object called printer deriving from the class PrintingClass and uses that object to print text. Your task is to write the PrintingClass class.
Program to complete: import java.util.Scanner; public class Things { public static void main(String args[]) { String characterString; Scanner reader = new Scanner(System.in); PrintingClass printer = new PrintingClass(); System.out.print("Type in the character string for printing: "); characterString = reader.nextLine(); printer.Print(characterString); } }
// Write the missing class here
Note: In this exercise the solution is part of a conversion unit where many classes have been declared. Because of this the classes are not declared as public using the public attribute.
Example output
Type in the character string for printing: John Doe
John Doe
My Class: class PrintingClass { public void print(){ System.out.println(characterString); } }
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???
I have to create a constructor with eight parameters containing both string and integers.the variables were supposed to be entered by user. but when I try to create an object of the class the IDE post error messages about the constructor.
public class hfiledriver { //the class name is hfile //after the main method I try creating an object of the class //after prompting the user to enter the data hfile hfile= new hfile(firstname, lastname, gender, age, weight, height); }
The one problem in my book was to create a constructor for different shirt features, which I did and ran successfully. Out of curiosity, I also added other methods to see if it would run if the parameters were different from the constructor. It keeps giving me a constructor error. So, my question is, am I able to create a class that uses a constructor with parameters and other methods without errors? I'm guessing there's no reason to since it would be wasted space since the constructor could do it but was just curious if it's possible.
Is everything from the constructor down (in the class) and Shirt.oneShirt (in the main) just a waste of time?
Here's my example:
public class Shirt//class name. { int collarSize;//data field. int sleeveLength;//data field. int pocketNumber;//data field public final static String MATERIAL = "cotton";//final data field for material. public Shirt(int collarSize, int sleeveLength, int pocketNumber)//start of constructor. {
