private int superCount = 0;
public void calculator(JFXButton buttonName,int price,String name,int count){
float percentage = Float.parseFloat(percentageButton.textProperty().get())/100;
totalPrice += price*percentage;
count++;
status.setText(name+" has been added");
String totalPriceString = String.format("%,.0f", totalPrice);
priceLabel.setText("£"+totalPriceString);
buttonName.setText(name+" : "+count);
}
public void addSuper(ActionEvent actionEvent) {
calculator(superButton,superPrice,"Super",superCount);
}
So I'm passing superCount into calculator. Then I'm incrementing count by 1. However, since that count is actually superCount (at least I thought it was) it's not actually changing superCount.
What am I doing wrong?
Worth pointing out that you don't need to pass it in if you've already declared supercount outside of these methods - you can just increment supercount from within calculator(). If they are in different classes:
Java is pass by value and not pass by reference. So if you pass a value into a method, you're not changing the original value, only the new value that you've passed in.
count only exists inside your calculator method. You can't change the value of supercount without returning a value from calculator.
// If you change calculator to return an it
public int calculator(...) {
return count;
}
Now you could do:
supercount = calculator(superButton,superPrice,"Super",superCount);
Related
Not sure where I'm going wrong with this. I've asked someone in my class and they said there should be an argument with "toonRijSterren". when I do this I just get more errors, could someone have a look and tell me where I'm going wrong?
public static void main(String[] args) {
int aantal = 0;
toonRijSterren(aantal);
toonSterrenVierkant(aantal);
}
public static void toonRijSterren(int mpAantal) {
while (mpAantal < 6) {
System.out.print(" * ");
mpAantal++;
}
}
public static void toonSterrenVierkant(int mpAantal) {
for (int mpAatal = 0; mpAantal < 6; mpAantal++) {
System.out.println(toonRijSterren());
}
}
ther error line is in the brackets of the last toonRijSterren());
toonRijSterren is void method which means it does not return any value and therefore you can not put it inside System.out.println() or you can not assign it to some variable.
toonRijSterren expects an int argument which you have missed while calling it.
Given below is an example of how you should call toonRijSterren:
public static void toonSterrenVierkant(int mpAantal) {
for (int mpAatal = 0; mpAatal < 6; mpAatal++) {
toonRijSterren(mpAantal);
}
}
You are not passing the argument when you call your method.
Try this:
System.out.println(toonRijSterren(mpAatal));
First of all, your function toonRijSterren takes an int type parameter (according to its declaration), so you need to pass to it another argument. For example:
toonRijSterren(mpAantal)
Second, the function toonRijSterren returns void. That means, it just does an operation (in this case, printing) without returning anything. What you're trying to do is to use its return value (which doesn't exist) as an argument to System.out.println, which causes an error (because println expects an argument of some type).
You could achieve what I think you're trying to do with the line:
toonRijSterren(mpAantal);.
The function itself prints the values, so the println here is unnecessary and causes an error.
You are missing the parameter in your toonSterrenVierkant() function where you calling toonRijSterren.
Here is the corrected version of your code:
public static void toonSterrenVierkant(int mpAantal) {
for (; mpAantal < 6; mpAantal++) {
toonRijSterren(mpAatal);
}
}
As your methed toonSterrenVierkant(int mpAantal) has a int parameter, you must pass an int value as an argument in the last toonRijSterren(). For example, replace the line System.out.println(toonRijSterren()); with System.out.println(toonRijSterren(1));
I have a method whose some parts of are repetitive. I managed to split the code in a way that the original method uses smaller methods many times. The problem is that when I pass some values as params to those new smaller methods and work with them, original values don't get updated. The actions I do are: value incrementation or removing items from arraylist. How do I update the original values using the smaller methods, not only the references? The only possible solution I came up with is to create a new class where I could have a setter for those values and update them. But are there easier/straightforward ways to solve it?
Part of the main method:
int numberOfBlocks = 0;
int currentBlock = 0;
int currentTime = 0;
ArrayList<Request> queue = new ArrayList<Request>();
if(queue.size != 0) {
updateStatus(queue, currentBlock, numberOfBlocks);
}
if(something else happens) {
removeFinished(queue, currentBlock);
}
Smaller methods:
private void updateStatus(ArrayList<Request> queue, int currentBlock, int numberOfBlocks) {
if (queue.get(0).getBlock() > currentBlock)
currentBlock++;
else
currentBlock--;
numberOfBlocks++;
}
private void removeFinished(ArrayList<Request> queue, int currentBlock){
if (queue.get(0).getBlock() == currentBlock) {
queue.remove(0);
}
}
First of all, if you pass a parameter in order for it to be changed in the method, your method should return the changed value, this will resolve your issue. If more then one value needs to be changed, then you are correct, primitives are passed y value and the invoking method doesn't see the changes made in the invoked method. So you should encapsulate those values in a wrapping class with setters and getters like you wanted to. That alone will resolve your problem. But also it would make sense for your method to return that class since it is modified. This is just a good stile
If the smaller methods are in the same class as the main method, simply don't pass them as parameters and the methods will use the class's fields. This is non-thread safe, but your class is non-thread safe already anyway.
class MyClass
{
int numberOfBlocks = 0;
int currentBlock = 0;
int currentTime = 0;
ArrayList<Request> queue = new ArrayList<Request>();
void myMainMethod() {
if(queue.size != 0) {
updateStatus();
}
if(something else happens) {
removeFinished();
}
}
private void updateStatus() {
if (queue.get(0).getBlock() > currentBlock)
currentBlock++;
else
currentBlock--;
numberOfBlocks++;
}
private void removeFinished() {
if (queue.get(0).getBlock() == currentBlock) {
queue.remove(0);
}
}
First i add new Popotnik in List popotnik depending on how big it is, which is working fine - function prostaMesta. Then i want to go through list popotnik and set popotnik value depending on where it is in for, but value of i will always be 0 everytime it is being called. Also i have break there as i only want to set one popotnik at the time. How should i increment (i) while having some sort of break in there?
Also if(popotnik.get(i) == null){} is not being called, but values inside popotnik are null(s)
private List<Popotnik> popotnik = new ArrayList<Popotnik>();
public void prostaMesta(List<Popotnik> popotnik, int sedez){
stanovanje.setPostle(sedez);
for(int i=0; i<stanovanje.getPostle(); i++){
popotnik.add(new Popotnik());
}
System.out.println(popotnik);
}
public void dodajPotnika(List<Popotnik> popotnik, Popotnik popotnik2){
for(int i=0; i<popotnik.size(); i++){
if(popotnik.get(i) == null){
setPopotnik(popotnik, i);
popotnik.set(i, popotnik2);
break;
}
}
System.out.println(getPopotnik());
}
public void setPopotnik(List<Popotnik> popotnik, int i){
this.popotnik = popotnik;
}
public List<Popotnik> getPopotnik(){
return popotnik;
}
Main class:
List<Popotnik> alPopotnik = new ArrayList<Popotnik>();
if(x.equals("p")){ //inside of a loop when prostaMesta() is being called
potovanje.prostaMesta(alPopotnik, sedez);
}
`if(x.equals("d")){` //inside of a loop when dodajPotnika() is being called
System.out.println("Vnesi ime: ");
String ime = skener.next();
Popotnik popotnik = new Popotnik(ime);
potovanje.dodajPotnika(alPopotnik, popotnik);
}
The if(popotnik.get(i) == null) is never true because objects on the list are not null. You initialize them in the for loop in prostaMesta.
If you have some fields inside the Popotnik class then they are null, but object itself is not.
You would need to do something like popotnik.get(i).getName() == null.
Besides, if you only want to add a number at the end of popotnik's name then it isn't necessary to initialize a list with empty objects.
You could just add objects to list using a different constructor.
For example popotnik.add(new Popotnik("Popotnik"+(popotnik.size()+1))).
It's not pretty but I think initialization like this here is not necessary.
I'm just new to Java OOP, and I hardly understand about the class and stuff. I tried to write some code to understand but I didn't succeed. Here is my code, I expected it to return the number of eggs but I don't know why it returns nothing.
class EggCounter {
private int egg;
{
egg = 0;
}
public void eggAdd()
{
egg = egg + 1;
}
public void eggBreak()
{
egg = egg - 1;
}
public void eggAddDozen()
{
egg = egg + 12;
}
public int getEgg()
{
return egg;
}
}
public class EggTest
{
public static void main(String[]args)
{
EggCounter egg = new EggCounter();
egg.eggAdd();
egg.eggAddDozen();
egg.eggBreak();
egg.getEgg();
}
}
It does return 12. Replace the egg.getEgg(); line in your main method with System.out.println(egg.getEgg()); and you will notice it prints 12.
It is returning, it's just that you do nothing with the return value of getEgg. What you need to do is store it into the variable or do something with it. return <value> only returns the given value to the callee, you must store it to use it. Example:
int eggCount = egg.getEgg();
System.out.println(eggCount);
Here, the assignment of eggCount calls egg.getEgg(). The call resolves when the number of eggs is returned, which assigns the return value to eggCount. Finally, it will print out eggCount. If you need the result of egg.getEgg() later, you can simply just output the following:
System.out.println(egg.getEgg());
How this works is the method egg.getEgg() is called. The return value is then resolved, which is passed into the print statement. This gets rid of storing it into a variable you can use later.
The question is:
Write the definition of a class Counter containing:
An instance variable named counter
of type int .
An instance variable named limit of type int .
A static int variable named nCounters which is initialized to 0 .
A constructor taking two int parameters that assigns the first one to counter and
the second one to limit . It also adds one to the static variable nCounters .
A method named increment . It does not take parameters or return a value ; if the
instance variable counter is less than limit , increment just adds one to the
instance variable counter .
A method named decrement that also doesn't take parameters or return a value ; if
counter is greater than zero, it just subtracts one from the counter .
A method named getValue that returns the value of the instance variable counter .
A static method named getNCounters that returns the value of the static variable
nCounters .
My Dilemma
The code works fine but I want to know the following:
Why is the first static private and the second one public?
My code:
public class Counter
{
private int counter;
private int limit;
private static int nCounters = 0;
public Counter (int x, int y)
{
counter = x;
limit = y;
nCounters++;
}
public void increment ()
{
if( counter < limit)
{
counter++;
}
}
public void decrement ()
{
if(counter > 0)
{
counter--;
}
}
public int getValue ()
{
return counter;
}
public static int getNCounters ()
{
return nCounters;
}
}
nCounters is a variable that you use to count the numbers of times the Class constructor has been called. It's static because is not a instance variable but a class variable (its value is shared by all the instances of that class).
nCounter is privated for encapsulate it. It can only be accessed outside the class by a read only method named getNCounters. Otherwise, I could access the value of nCounter and change it directly causing the value of classes created not reliable anymore.
You can read more about encapsulation and static methods and variables to understanding better your code.
The first static variable nCounters is private, because you want to control it in your class - you do not want any code outside of Counter to modify it. But you want to make it possible to read its value outside of Counter, thus the getNCounters() method is public.