Im trying to add a dog (nyHund) which is created in a different class, to an Arraylist i created using a constructor in another class, but whenever i try to use the Arraylist in the "register" class, im getting the error that the arraylist name can't be resolved.
First class:
public class Hund {
private String namn;
private int ålder;
private double vikt;
private String ras;
public Hund(String hundnamn, int hundålder, String hundras, double hundvikt) {
this.namn = hundnamn;
this.ålder = hundålder;
this.ras = hundras;
this.vikt = hundvikt;
}
public String getNamn() {
return namn;
}
public int getÅlder() {
return ålder;
}
public double getSvanslängd() {
if (ras=="tax"){
return 3.7;
}else{
return ((vikt*ålder)/10);
}
}
public String toString() {
return namn + "\n" + ålder + "\n"+ras+"\n"+vikt+"\n"+getSvanslängd();
}
}
Second Class
import java.util.ArrayList;
public class testning {
public static void main(String[] args) {
Hund nyHund = new Hund("Daisy", 13, "labrador", 22.3);
System.out.println(nyHund.toString());
Register.läggTillHund(nyHund);
}
}
And the Third class:
import java.util.ArrayList;
public class Register {
public static void läggTillHund(Hund nyHund){
hundRegister.add(nyHund);
System.out.println(nyHund);
}
private Register(){
ArrayList<Hund> hundRegister = new ArrayList<Hund>();
}
}
The problem i am experiencing is with "hundRegister.add(nyHund)"
any thoughts? or pointers where im going wrong? (very new at Java)
Best Regards
Oskar
The ArrayList you've created is local to your Register constructor. Declare it inside the class, but outside the constructor, as an instance variable, so it's in scope throughout the class.
public class Register {
private ArrayList<Hund> hundRegister;
private Register(){
hundRegister = new ArrayList<Hund>();
}
}
Additionally, it's unclear why the constructor is private. Nothing else can access that constructor. I would make it public.
Also, in getSvanslängd, replace ras=="tax" with "tax".equals(ras). See How do I compare strings in Java?.
Related
I have three classes: Labradors, Kennels and Show. The Kennel contains a private ArrayList of
Labradors. As shown:
Labradors.java:
public class Labradors {
private String name;
private String description;
public Labradors(String n, String d) {
name = n;
description = d;
}
public String getName() {
return name;
}
}
Kennel.java:
import java.util.ArrayList;
public class Kennel{
private ArrayList<Labradors> labs;
public Kennel() {
labs = new ArrayList<Labradors>();
}
public void addDog(Labradors l) {
labs.add(l);
}
}
and
Show.java
class Show
{
public static void main(String args[])
{
Labradors Dave = new Labradors("Dave", "Good dog!");
Labradors Bob = new Labradors("Bob", "Likes tummy rubs!");
Kennel niceHome = new Kennel();
niceHome.addDog(Dave);
niceHome.addDog(Bob);
for (Labradors lab: niceHome.labs ) {
System.out.println(lab.getName());
}
}
}
My for-each loop in Show gives me the following error:
Show.java:12: error: labs has private access in Kennel
for (Labradors lab: niceHome.labs ) {
^
1 error
Clearly one solution would be to make the ArrayList public, but my understanding of encapsulation is that best practice means it should be private and a Getter written. But how do I do this?
I feel this should have a really easy answer, but I'm having difficulty tracking it down...
NB - I'm using openjdk version 11.0.6 on Ubuntu 19.10.
Inside Kennel Class make a getter function
import java.util.ArrayList;
public class Kennel{
private ArrayList<Labradors> labs;
public Kennel() {
labs = new ArrayList<Labradors>();
}
public void addDog(Labradors l) {
labs.add(l);
}
public ArrayList<Labradors> getLabs(){
return this.labs;
}
}
Then access from main function like this
class Show
{
public static void main(String args[])
{
Labradors Dave = new Labradors("Dave", "Good dog!");
Labradors Bob = new Labradors("Bob", "Likes tummy rubs!");
Kennel niceHome = new Kennel();
niceHome.addDog(Dave);
niceHome.addDog(Bob);
for (Labradors lab: niceHome.getLabs()) {
System.out.println(lab.getName());
}
}
}
I want to create the below class
associatename:String
workstatus:String
associate() :constructor
getassociatename():String
setassociatename(String):void
getworkstatus()String
tracksassociatestatus():int
setworkstatus(String):void
The trackAssociateStatus method takes the number of days as argument and sets the work status of the associate based on the number of days. The first 20 days they learn “C”, the next 20 days they learn “Java” In the Main class invoke the trackAssociateStatus method and find the work status and display the output.
output:The associate abc work status:Project phase
I tried this....But i got error
//associate class
public class associate{
private int associatename;
private String workstatus;
private int days;
void associate()
{
getassociatename();
setassociatename();
getworkstatus();
tracksassociatestatus();
setworkstatus();
}
public int getassociatename()
{
return associatename;
}
public void setassociatename(int associatename)
{
this.associatename=associatename;
}
public String getworkstatus()
{
return workstatus;
}
public void tracksassociatestatus(int days)
{
if(days<20)
setworkstatus("C");
else
setworkstatus("Java");
}
public void setworkstatus(String workstatus)
{
this.workstatus=workstatus;
}
}
//main class
associate a =new associate();
Scanner in=new Scanner(System.in);
int associateid=0;
String workstatus=null;
int days=0;
System.out.println("Enter the associateid:");
associateid=in.nextInt();
a.associateid=(associateid);
System.out.println("Enter the no of days:");
days=in.nextInt();
a.trackassociatestatus();
System.out.println("The id is "+a.getassocaiteid()+" work status "+a.getworkstatus());
Based on your (seemingly) UML spec, your class would look like the following:
public class Associate {
private String associateName;
private String workStatus;
public Associate() {
// This constructor is optional, a no-args constructor is added by the compiler to any class not explicitly naming a constructor.
}
public String getAssociateName() {
return associateName;
}
public void setAssociateName(String associateName) {
this.associateName = associateName;
}
public String getWorkStatus() {
return workStatus;
}
public void setWorkStatus(String workStatus) {
this.workStatus = workStatus;
}
public int tracksAssociateStatus() {
// TODO write logic here
return 1; // TODO change to whatever you need to return
}
}
You were specifying int for getAssociateName, when associateName is a String. This won't work; you need your getter return type to be the same as your field data type, or you need to convert the data to the method's return type. (The former is best practice).
Constructors don't specify a type, the class name is used and the compiler will understand what you want to do (which is return a new instance of the class). Therefore, your void associate() will tell the compiler "create a method called associate that doesn't return anything".
Well, would be nice if you provide the error itself for us.
But meanwhile, have you notice that your tracksassociatestatus method recieves an integer parameter days, and your constructor passes nothing to it?
So try changing your constructor to be something like:
Public associate() {
getassociatename();
setassociatename();
getworkstatus();
tracksassociatestatus(10);
setworkstatus();
}
For a cleaner code, check the other answer.
If you still have errors, please share them.
import java.util.*;
public class Associate
{
private String associateName;
private int workStatus;
private int days;
Scanner sc = new Scanner(System.in);
public String getAssociateName()
{
System.out.println("Enter the Associate id:");
associateName = sc.nextLine();
return associateName;
}
public void setassociatename(int associatename)
{
this.associateName=associateName;
}
public String tracksAssociatename()
{
return associateName;
}
public int getWorkStatus()
{
System.out.println("Enter the number of days");
days = sc.nextInt();
return days;
}
public void setWorkStatus(String workStatus)
{
this.workStatus=workStatus;
}
enter code here
public `enter code here`int tracksAssociateStatus()
{
return days;
}
public static void main(String args[])
{
Associate obj = new Associate();
obj.getAssociateName();
obj.getworkstatus();
System.out.println("The Associate name "+obj.tracksAssociatename()+" work Status "+obj.tracksAssociateStatus());
}
}
I have 3 classes, say: ShareType, ShareTypesTrue and Main.
public class ShareType {
public String shareTypeName = "";
public String noOfShare = "";
public String parValue = "";
public void setShareTypeName(String shareTypeName) {
this.shareTypeName = shareTypeName;
}
public void setNoOfShare(String noOfShare) {
this.noOfShare = noOfShare;
}
public void setParValue(String parValue) {
this.parValue = parValue;
}
}
public class ShareTypesTrue {
public List<ShareType> shareType;
public void setShareType(List<ShareType> shareType) {
this.shareType = shareType;
}
}
public class Main {
ShareTypesTrue sharetypetrue = new ShareTypesTrue();
sharetypetrue.add(shareTypeName);
}
Now my problem is i need to set shareTypeName to a value under the class ShareTypesTrue. Meaning i have to use ShareTypesTrue to call on the Sharetype class and set the shareTypeName.
Anyone has an idea?
NOTE: I cant change/add code in the first 2 classes except in main. i just need to find a way to get around this.
Thanks Alot
Please check below code for Main class.
import java.util.ArrayList;
import java.util.List;
public class Main {
public static void main(String args[]){
ShareTypesTrue sharetypetrue = new ShareTypesTrue();
//Create object
ShareType shareType = new ShareType();
shareType.setShareTypeName("Original Name");
//Create list
List<ShareType> shareTypes=new ArrayList<ShareType>();
shareTypes.add(shareType);
//Attach it to share
sharetypetrue.setShareType(shareTypes);
//Print
for(ShareType shareTypesMember:sharetypetrue.shareType){
System.out.println(shareTypesMember.shareTypeName);
}
//Editing it.
for(ShareType shareTypesMember:sharetypetrue.shareType){
shareTypesMember.shareTypeName = "Updated Name";
}
//Print
for(ShareType shareTypesMember:sharetypetrue.shareType){
System.out.println(shareTypesMember.shareTypeName);
}
}
}
Use Sharetype class to set the shareTypeName
ShareType share = new ShareType();
share.setShareTypeName("name");
share.setNoOfShare("no");
share.setParValue("val");
List<ShareType> shareType = new ArrayList<ShareType>();
shareType.add(share);
use ShareTypesTrue to set Sharetype
ShareTypesTrue sharetrue = new ShareTypesTrue();
sharetrue.setShareType(shareType);//pass ShareType as list
If you want to set the 'name' in ShareType, what prevents you from doing the below:
class ShareTypeTrue_Extended extends ShareTypeTrue{
protected shareTypeName;
public ShareTypeTrue_Extended(String shareTypeName){this.shareTypeName=shareTypeName;}
public void setShareType(List<ShareType> shareType) {
for(ShareType s: shareType)s.setShareTypeName(this.shareTypeName);
super.setShareType(shareType);
}
}
I am struggling with making this code work. Here is my code. First class:
public class PersonalAccount extends Account{
private String cardNumber;
private String cardType;
public ArrayList<PersonalAccount> personalAccounts;
public int personal;
private PersonalAccount(String first, String last, String accountNumber, String cardNumber, String cardType){
super(first, last, accountNumber);
this.cardNumber = "";
this.cardType = "";
}
public void addPersonalAccount(PersonalAccount aPersonalAccount){
personalAccounts.add(aPersonalAccount);
}
public void getNumberOfPersonalAccounts(){
personal = personalAccounts.size();
}
public void listAccounts(){
for (PersonalAccount personalaccount : personalAccounts){
System.out.println("Personal Accounts");
System.out.println(personalaccount);
}
}
public void findAccount(){
int index = 0;
boolean found = false;
while(index < personalAccounts.size() && !found){
PersonalAccount personalaccount = personalAccounts.get(index);
if (personalaccount.getaccountNumber().equals(accountNumber)){
found = true;
}else{
index++;
}
}
}
}
When attempting to create an instance of this class in another class, it instead creates an instance of the PersonalAccount object. Is there a way around this issue? I am very new to Java and BlueJ it should be noted.
EDIT: sorry I should clarify. I'm trying to call the methods from this class in another class. But when declaring
PersonalAccount class1 = new PersonalAccount();
I get the error: constructor PersonalAccount in class PersonalAccount cannot be applied to given types.
I am trying to call the method on a button click (where numAcc is the button):
numAcc.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent evt)
{
int personal;
personal = class1.getNumberOfPersonalAccounts();
}
});
You dont have a default constructor so you cannot create a PersonalAccount like this:
PersonalAccount class1 = new PersonalAccount();
You have to pass the parameters first, last, accountNumber, cardNumber, cardType. It should be something like this:
PersonalAccount class1 = new PersonalAccount("FirstName", "Last_Name", "123456", "123456789", "Visa");
Read this: http://www.dummies.com/how-to/content/how-to-use-a-constructor-in-java.html
You don't have a zero-argument constructor for PersonalAccount which is why the given statement would fail.
Is that the problem you are having?
The problem is here that the constructor is private:
private PersonalAccount(String first, String last, String accountNumber, String cardNumber, String cardType)
Two things:
You need to change your constructor such that it is public so that it is accessible:
public PersonalAccount(String first, String last, String accountNumber, String cardNumber, String cardType)
The next thing is to supply parameters such as first, last, accountNumber etc. However, if you declare: public PersonalAccount(), then you would not need to supply arguments when you instantiate the class.
You should now be able to call the methods of this class!
This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 8 years ago.
been struggling with this problem since a couple of hours. Including looking through the previous questions answered. (Im really new in Java, basicly started a couple of days ago)
it keeps giving me NullpointerExceptions between Register.läggTillhund(nyHund); in the first class and hundRegister.add(nyHund); in the second class.
I have no idea what might be causing them. Does anyone have Ideas?
The purpose of the code (when finished) is to add an object from the 3rd class, into a list in the secondclass using the firstclass as the "main program".
Thanks for the help!
Oskar
First Class (Main)
public class testning {
public static void main(String[] args) {
Hund nyHund = new Hund("Daisy", 13, "labrador", 22.3);
System.out.println(nyHund.toString());
System.out.println(nyHund);
Register.läggTillHund(nyHund);
}
}
Second Class:
import java.util.ArrayList;
public class Register {
private static ArrayList<Hund> hundRegister;
public static void läggTillHund(Hund nyHund){
hundRegister.add(nyHund);
System.out.println(nyHund);
}
public Register(){
hundRegister = new ArrayList<Hund>();
}
}
Third Class
public class Hund {
private String namn;
private int ålder;
private double vikt;
private String ras;
public Hund(String hundnamn, int hundålder, String hundras, double hundvikt) {
this.namn = hundnamn;
this.ålder = hundålder;
this.ras = hundras;
this.vikt = hundvikt;
}
public String getNamn() {
return namn;
}
public int getÅlder() {
return ålder;
}
public double getSvanslängd() {
if ("tax".equals(ras)){
return 3.7;
}else{
return ((vikt*ålder)/10);
}
}
public String toString() {
return namn + "\n" + ålder + "\n"+ras+"\n"+vikt+"\n"+getSvanslängd();
}
}
You're accessing static method. In this case constructor never working. Use private static ArrayList<Hund> hundRegister = new Arraylist<>() ;and delete the constructor. To see what's going on add System.out.println line to construct and you'll see it will never works