I think the following code should trigger a compiler error.
public final class IPoint3D {
private double x;
private double y;
private double z;
public IPoint3D(double x, double y, double z)
[Code] .....
I have this piece of code I wrote a while ago to test something. The issue is accessing a private field of Base class in Base but of a Derived object.
Here is the code:
class Base
{
private int x;
public int getX()
[Code]....
The commented code does not work but casting d to Base does.
Forgot to mention that the compilation error is that x has private access in Base.
public class StudentNumber {
/*
public StudentNumber(){
System.out.println("test");
}
*/
private char c='W';
public StudentNumber(float i){
System.out.println(i);
[Code] ....
Exception in thread "main" java.lang.RuntimeException: Uncompilable source code - c has private access in extention.pkgsuper.StudentNumber
at extention.pkgsuper.ExtentionSuper.main
I did cast type. So what's the problem?
Being new to java I am a bit lost as to why my session attribute for this banking app wont add the deposits to the session var... it just keeps going back to the amount I set it to originally - so if I set the beginning balance to 3000 then deposit 100 it becomes 3100, but if I then try deposit another amount eg. a extra 200 it becomes 3200 not 3300 like it should be !!
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import java.net.*;
import java.text.DecimalFormat;
public class SessionBank extends HttpServlet
[Code] .....
I have come across some code where the method signature is like,
public methodName(final String argument) {
...
}
I fail to grasp why final is needed here. Is it only because of the field immutabilty? What big picture am I missing in this case?
I am getting the above error and am not sure which direction to proceed. In the class, the only way we have discussed getting user input is by System.in.read. I have searched and apparently found better methods for getting user input, but wanted to stick with what has been presented thus far.
Assignment Directions:
1. Create a new class named “valuemethod”
2. Create a new method named “Main”
3. In Main Write the code that will call the method EnterPay and YearlySal
4. Create a new method named “EnterPay”
5. In the EnterPay method Write the code that asks the user to input their hourly wage. Use the formula to calculate their yearly salary: wage * 2040. Return the yearly salary to the main method
6. In the main method write the code that will display this: “Your yearly salary is:
Java Code:
package valuemethod;
public class Valuemethod
{
public static void main(String[] args)
//throws java.io.IOException -- moved to EnterPay
[Code] .....
From the tutorial:instance variables can be declared in class level before or after use.But the code below does not compile. Why?
Java Code:
public class MainApp {
i=5;
public static void main(String[] args) {
System.out.println("Hello World");
}
int i;
} mh_sh_highlight_all('java');
The 2 minute drill from page 69 SCJP kathy and bert book, says regarding Interfaces, that - "A legal nonabstract implementing class must not declare any new checked exceptions for an implementation method."
When I try the below given code in eclipse , it does not throw any errors . (Here I have tried to throw NullPointerException from testFunc whereas the interface function throws IllegalStateExc)
package abstracttesting;
public class StaticCheck implements check{
public void testFunc() throws NullPointerException{
// TODO Auto-generated method stub
} public static void main(String[] args) {
// TODO Auto-generated method stub
}
}
interface check{
void testFunc() throws IllegalStateException;
}
public class Ball {
private int a=show();
int b;
Ball()
{
b=20;
}
public static void main(String args[])throws Exception {
System.out.println(new Ball().a);
}
private int show()
{System.out.println(b);
return b;
}
}
I wanted to know when are the objects created ? when are they initialized? and how is show() getting called without any reference or "this" ?
While reading the design patter book, i got one doubt ,There is a List an interface having sub classes ArrayList, LinkedList etc.,
Q1) My question is Why they declared the List as interface rather than Abstract class?
Q2) i read some site -
List l = new ArrayList(); Why it is GOOD line?
ArrayList l = new ArrayList() ; Why it is BAD line?
Answer required with detailed information for Q1 and Q2.
A method is declared to take three arguments. A program calls this method and passes only two arguments.Will it take the third argument as
1 null
2 void
3 zero
4 Compilation error
So I'd like to know what all the statement, not sure if it's the correct way of calling them but I'd like to know what like all of those purple-ish colored words in eclipse actually mean.Here's what I know so far, so if you can add some stuff to it or just correct me:
public - can be accessed by different classes.
private - can't be accessed by different classes.
static - adds a '.' which pretty much lets you like use methods on it? Not really sure about this one.
final - a final value of a variable meaning it couldn't and willn't change?
super - I have no clue, maybe something that has to be executed first? Not sure.
void - bassicly you don't have to use return as it doesn't return any value.
this - Uh-.. I think it has something to do with the class this keyword has been entered into, not quite sure what it does though.
I assume there are alot more but I am just not sure about these common ones, what the actually do and what's their purpose?
What happened when we use main() as a private. . . . .???????
View Replies View RelatedI am creating a slot machine using eclipse. I am trying to get the "winnings" JTextField to be updated in a way so that when the random images have been selected it adds to the number that is already displayed in the JTextField as opposed to what it is doing at the minute which is just displaying how much was won on that particular spin. I am also struggling to set a code for when noting is won, nothing is added. My code is below.
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
import java.util.*;
import javax.swing.Timer;
[Code] ....
It isn't messing up it just keeps making me make my arraylist static and i'm not sure why.
public class driver
{
private static ArrayList<AddItems> items;
public driver()
[Code]....
I'm working on a project that contains multiple classes. Each class contains and must contain only PRIVATE variables. Here's my issue. When my test code calls for a new instance of "StudentClass" as so:
StudentClass studentClass = new StudentClass(offeredClass.getClassIdNumber(),
offeredClass.getClassName(),
offeredClass.getClassroom());
The corresponding constructor won't let me initialize it's variables because they are declared private within another class, as shown here:
StudentClass (float classIdNumber, String className, Classroom room){
this.classIdNumber = classIdNumber;
this.className = className;
this.room = room;
}
When getClassName, getClassroom, and getClassIdNumber are passed to a toString() method elsewhere in my test code. the output is returned just fine. When passed through the StudentClass, I'm getting Null across the board.
The first is clear , new Person().printPerson(); displays Person but for the second : new Student().printPerson(); it accesses the Student constructor that points to the Person class => object. It builds the Person instance then goes back to the Student constuctor .Both methods are private and to my knowledge invisible one to the other , except that you cant run the the Person one because it's private so the only one in the Student class is the Student one . Guess it 's incorrect , but why ? (is because private methods cant be overriden and somehow the super class one always has priority ? , even if it's private?)
public class Test {
public static void main(String[] args) {
new Person().printPerson();
new Student().printPerson();
[code]....
I have a project for a class where I'm supposed to be something with private arrays and private integers and I still don't understand the point of private anything within java. if I want to change a variable I'll change it. if I want it to stay the same I'll leave it the same. so what point is all this private/public nonsense unless I'm trying to stop hackers or something?
View Replies View RelatedJava Code:
import java.util.Scanner;
import java.util.ArrayList;
public class Problem1
{
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
ArrayList<String> list = new ArrayList<String>();
[Code] ....
There is an error and says that my ArrayList has private access. I can't figure out how to fix it.
The code runs but when I enter "Quit", the program just stops. The arraylist isn't printed out?
When creating a class with a constructor, why does one have to create private variables (attributes) to be used as parameters by the object? The object's parameters will be set to be exactly equal to the private variables (attributes), so what is the point of having the private variables (attributes) Why are both private variables (attributes) and parameters needed when they are set to be equal each other anyway?
View Replies View RelatedI just recently started learning about encapsulation, how to set variables private and only accessible to other classes through setters() and getters(). I've seen a couple of programming examples, perhaps not enough but some from here, and I sort of built the assumption that by default all variables need to be private. to make things more clear, here's a card dealer I made which simply
1- generates a fulll deck of 52 cards
2- lets user decide how many players, with 5 as Max number allowed as each player is dealt 10 cards.
3- deal cards
I approached this by making A deck , card , player and game class
import java.util.ArrayList;
public class Deck {
//an Object of this Class would generate a full deck ie an ArrayList of 52 Cards
private String[] suits={"Spades","Diamond","Clubs","Hearts"};
private int[] number={1,2,3,4,5,6,7,8,9,10,11,12,13};
ArrayList<Cards> deck= new ArrayList<Cards>();
[code]....
I can understand why for example Deck class's suit and number arrays are set to private , as they only need to be accessed by this class only. however, both the Deck class's deck arraylist and the Player class arraylist are not private, as I need to transfer these values from one to the other and it felt to me that setting them to private would make it more difficult to deal with them, but what I did instead is to set the Game class dealCard(), which is the only method that have access to them as private. does this achieve the same effect or do I need to set both of these arrayList to private?a follow up question, this is more related to the actual card dealer program, in this code
private void dealCards(){
for(int x = 0 ; x < playerCount ; x++){
for(int y = 0 ; y < 10; y++){
playerList.get(x).pile.add(deck.deck.get(0));
deck.deck.remove(0);
}
}
}
is there an API in ArrayList class that moves(adds to receiver and remove from giver) element across ArrayLists?
I came across the below
1) When a variables are declared "Private" How should it be accessed from the driver class ? Sometimes i get an error in driver class saying "your variable is declared Private" why am I getting this error ...
The document says "Private" declared variables should be accessed only through methods. What does that mean.
As below code showing that you cannot directly access the private variable as i understood,
public class EncapsulationDemo{ private int ssn;
private String empName; private int empAge; //Getter and Setter methods
public int getEmpSSN(){ return ssn; }
public String getEmpName(){ return empName;
[Code] .....
I have a class named Base and a private variable named _hopcount i have 10 instances of class base i use _hopcount as creteria to some if but other instances edit _hopcount so i want to prevent _hopcount edit by other instances; I want to have private variable which other instances of same class can't modify it.
public class Base extends TypedAtomicActor {
private int _hopcount = 0;
if(_hopcount <= 3) {
some code;
}
public function() {
_hopCount += 1;
}
}
I want to make a private method that will change the value of a instance variable like this:
String bla = "bla bla bla";
private void changeString (String x) { x = "eee";}
changeString(bla);
Now value of the variable bla should be "eee" but its not, it is stil "bla bla bla".
I have problems with private static void print section, something is missing? And in case 4, I want it to stop the program(end the loop) but it keeps going.
import java.util.Scanner;
import java.util.ArrayList;
public class Dogregister16 {
public static ArrayList<Dog> dogregister = new ArrayList();
private static Scanner keyboard = new Scanner(System.in);
public static void main(String[] args) {
initiate();
[Code] ....
case 4:
System.exit(0);
System.out.println("Exit program");
}
}
}
}