I've created this method and I'm unsure why it says there's a missing return statement. do I need to change the print to a return? (it's the method at the very bottom) I'm a bit of a Java beginner so any help will be appreciated!
public class Book {
private String title;
private String author;
private int copies;
private boolean borrowed;
public Book( String inAuthor, String inTitle, int inNumberOfCopies ) {
this.author = inAuthor;
this.title = inAuthor;
this.copies = inNumberOfCopies;
}
public void borrowed() {
borrowed = true;
}
public void rented() {
borrowed = true;
}
public void returned() {
borrowed = false;
}
public boolean isBorrowed() {
return borrowed;
}
public String getAuthor() {
return this.author;
}
public static String getTitle() {
return getTitle();
}
public int getTotalCopies() {
return this.copies;
}
public int getAvailableCopies() {
}
public void withdrawCopy() {
int found = 0;
for (Book b : Library.getListOfBooks()) {
if (b.getTitle().equals(title)) {
if (found == 0) {
found = 1;
}
if (!b.isBorrowed()) {
b.borrowed=true;
found = 2;
break;
}
if (found == 0) {
System.out.println("Sorry, this book is not in our catalog.");
} else if (found == 1) {
System.out.println("Sorry, this book is already borrowed.");
} else if (found == 2) {
System.out.println("You successfully borrowed " + title);
}
}
}
}
public String returnCopy() {
boolean found = false;
for (Book book : Library.getListOfBooks()) {
if (getTitle().equals(title) && book.isBorrowed()) {
book.returned();
found = true;
}
if (found) {
System.out.println("you successfully returned " + title);
}
}
}
}
public String returnCopy()
String after public means that this method will return a String.
Your public String returnCopy() is currently not returning anything.
If you don't want to return anything, you can use void like this:
public void returnCopy(){
// code
}
Same issue with public int getAvailableCopies(), this is supposed to return an int but you are not returning anything.
Be careful:
this method:
public static String getTitle() {
return getTitle();
}
is a recursive method without a base condition. This will cause an error and force your application to crash.
You've defined the method as returning a String but you don't return a value anywhere in the method body. Simplest fix is probably to change the return type to void...
public void returnCopy() {...
}
All the above answer are pointing to the same issue, you have defined methods that are breaking the contract about what they return..
In you code you have as well something like this:
public int getAvailableCopies() {
}
so you are telling the compiler, you have a method with the name getAvailableCopies, it takes no params and return an integer.
BUT if you don't return anything, then you are contradicting your own method, your own contract, this is an enough reason for a compiler to complain...
Conclusion:
keep in mind the information that defines the method.
Related
I'm implementing custom logic in setters and enums in realm object class like this.-
public class SellerProducts extends RealmObject{
public Boolean isValid=true;
public String is_valid="";
public String quantity;
public int quantity_;
public String enumvalue;
public void setIs_valid(String is_valid){
if (is_valid.equals("0")) {
this.isValid = false;
}
this.is_valid=is_valid;
}
public String getIs_valid(){
return this.is_valid;
}
public void setQuantity(String quantity){
this.quantity=quantity;
try {
quantity_ = Integer.parseInt(this.quantity);
} catch (NumberFormatException e) {
e.printStackTrace();
}
if (!this.isValid) {
setEnum(ProductType.IN_ACTIVE);
} else if (this.quantity_ <= 0) {
setEnum(ProductType.OUT_OF_STOCK);
} else {
setEnum(ProductType.ACTIVE);
}
}
public String getQuantity(){
return this.quantity;
}
public enum ProductType {
ACTIVE, IN_ACTIVE, OUT_OF_STOCK
};
public void setEnum(ProductType val) {
this.enumvalue=val.toString().toUpperCase();
}
public ProductType getEnum() {
return ProductType.valueOf(enumvalue);
}
}
when i am calling getEnum from the other fragment class it is returning null exception like this
*java.lang.NullPointerException: name == null
at java.lang.Enum.valueOf(Enum.java:189)
at com.localwizard.realm_db.SellerProducts$ProductType.valueOf(SellerProducts.java:331)
at com.localwizard.realm_db.SellerProducts.getEnum(SellerProducts.java:348)*
I'm new to realm so I don't know where I'm wrong?
Ashish, i think you are not setting the ProductType enum and trying to get it and you geeting the exception. Here is the code which i have tried and it is working fine -
public class OtherFragment {
public static void main(String[] aa)
{
SellerProducts sp = new SellerProducts();
sp.setQuantity("10"); // setting the quantity
System.out.println(sp.getEnum()); // ACTIVE is set as Enum
System.out.println(sp.getQuantity()); // 10
System.out.println(sp.getEnum() == ProductType.ACTIVE); // true
sp.setEnum(ProductType.IN_ACTIVE); // Now IN_ACTIVE is set
System.out.println(sp.getEnum() == ProductType.ACTIVE); // false
}
}
If this is not what you want then please add your peace of code, how you meant to set the quantity and trying to get the enum value.
If it answers your question then please accept the answer.
heres my code for a library application
package com.accenture.totalbeginner;
public class Person {
private String name;
private int maximumbooks;
public Person() {
name = "unknown name";
maximumbooks = 3;
}
public String getName() {
return name;
}
public void setName(String anyname) {
name = anyname;
}
public int getMaximumbooks() {
return maximumbooks;
}
public void setMaximumbooks(int maximumbooks) {
this.maximumbooks = maximumbooks;
}
public String toString() {
return this.getName() + " (" + this.getMaximumbooks() + " books)";
}
public boolean equals(Person p1) {
if(!this.getName().equals(p1.getName())) {
return false;
}
if(!this.getMaximumbooks().equals(p1.getMaximumbooks())) {
return false;
}
return true;
}
}
(!this.getMaximumbooks().equals(p1.getMaximumbooks()))
this is saying cannot invoke .equals on primitive type(int)
I know what that means, but I have tried everything and I can't think how to correct it.
If you need any of the code from other classes let me know.
equals() is used for Objects (String, Integer, etc...)
For primitives like int, boolean, char etc, you have to use ==
getMaximumbooks() returns a primitive type int not an Object. You have to compare it with == or in you case != (not equals)
if (this.getMaximumbooks() != p1.getMaximumbooks())
{
return false;
}
return true;
Just use == if you're comparing primitives.
Also, try not to use getters when working into the class because you have already access to all the fields (private or not).
public boolean equals(Person p1)
{
return this.maximumBooks == p1.getMaximumBooks();
}
Cannot invoke equals(int) on the primitive type int
.equals() is a method which is used only in objects
for int , double just as in the picture I have attached, use (==)
e.g (int a == int b)
I need to write a Java enumeration LetterGrade that represents letter grades A through F, including plus and minus grades.
Now this is my enumeration code:
public enum Grade {
A(true),
A_PLUS(true),
A_MINUS(true),
B(true),
B_PLUS(true),
B_MINUS(true),
C(true),
D(true),
E(true),
F(false);
final private boolean passed;
private Grade(boolean passed) {
this.passed = passed;
}
public boolean isPassing() {
return this.passed;
}
#Override
public String toString() {
final String name = name();
if (name.contains("PLUS")) {
return name.charAt(0) + "+";
}
else if (name.contains("MINUS")) {
return name.charAt(0) + "-";
}
else {
return name;
}
}
What I am confused about is writing the main program. I think it could be quite straightforward but I have no clue on how to start it.
I don't want the whole code. Just a few lines to give me a head start. The rest I will try to figure out on my own.
I imagine you have a Student class that looks like this:
class Student {
protected Grade grade = null;
public Student(Grade g) {
this.grade = g;
}
}
Then you simply add a method in this class calling the isPassing method from your enum:
public boolean isPassing() {
if (this.grade != null)
return this.grade.isPassing();
return false;
}
This is supposing the passed boolean in Grade are correctly set and are invariant.
So I'm having this problem with adding an element to an ArrayList
I have a class Media with 3 fields and another class Mediatheque with 1 field(which is an ArrayList).
Let's say I have:
A Mediatheque media = new Mediatheque
An equals(Media m) method in class Media < (important method)
I need to write a method add(Media m) which:
If the media.contenu does contain an element equals to the Media m I want to add, I must NOT add it and increase the nbEx field of the element contained in media.contenu
-Else I can add it using the add method provided by the ArrayList ( This doesn't seem too hard)
So I tried to write a contains(Media) method which uses the equals(Media m) method I wrote for the Media class and then use the contains method in the add method.
My question is that how am I supposed to write the add method? < (The Question)
I must write this using ArrayList, it is a school assignment
Sorry about the long code and the bad English, I'm a complete noob.
Here is my Media class:
package Ex1;
public class Media {
private final String support; // Format: Book, CD, DVD,etc...
private final String titre; // Title
private int nbEx; // Number of copy
public Media(String titre, String support){
this.titre = titre;
this.support = support;
this.nbEx = 1;
}
public Media (){
titre = "";
support = "";
nbEx = 0;
}
public boolean equals(Media m){
boolean equality = false;
if (m instanceof Media){
equality = (this.titre.equals(m.titre) && this.support.equals(m.support));
}
return equality;
}
public Media(Media m){
this.titre = m.titre;
this.support = m.support;
}
}
And here is my Mediatheque class:
import java.util.ArrayList;
import static java.lang.System.out;
public class Mediatheque {
ArrayList<Media> contenu;
public Mediatheque(){
this.contenu = new ArrayList<Media>();
}
public Mediatheque(Mediatheque m){
this.contenu = m.contenu;
}
public boolean contains(Media m){
int i = 0;
boolean contain = this.contenu.get(i).equals(m);
for(i = 0; i<this.contenu.size(); i++){
if(contain)
break;
}
return contain;
}
public int indexOf(Media m){
boolean retVal = this.contenu.get(i).equals(m);
for(Media i : contenu){
if(contain)
break;
}
return i;
}
public void add(Media m){
if(this.contains(m)){
this.contenu.get(this.contenu.indexOf(m)).setNbEx(this.contenu.get(this.contenu.indexOf(m)).getNbEx()+m.getNbEx());
}else{
this.contenu.add(m);
}
}
My question is that how am I supposed to write the add method?
Sorry about the long code and the bad English, I'm a complete noob.
Thank you!
As stated by #NeplatnyUdaj in the comment of your question, the use of a Map would greatly improve your code. Instead of recording the number of medias inside the Media object, use a HashMap<Media, Integer> to store your data in this way:
new HashMap<Media, Integer> map = new HashMap<Media,Integer>();
if ( map.containsKey(key) ) {
map.put(key, (map.get(key) + 1));
} else {
map.put(key, 1);
}
Where key is the media. (m in your code)
When one overrides the equals() method, one is also supposed to override the hashCode() method. The equals() method takes an Object parameter. Here's how your Media class should look like:
// Media.java
public class Media
{
private final String support;
private final String title;
public Media(String title, String support)
{
this.title = title;
this.support = support;
}
public Media(Media media)
{
this(media.title, media.support);
}
#Override
public int hashCode()
{
return 31 * title.hashCode() + support.hashCode();
}
#Override
public boolean equals(Object object)
{
if (object instanceof Media)
{
Media media = (Media) object;
return media.title.equals(title) &&
media.support.equals(support);
}
return false;
}
}
Then use a HashMap to map the media with its number of copies. Here's how that's done:
// MediaMap.java
import java.util.HashMap;
import java.util.Map;
public class MediaMap
{
// Media to its Number of Copies mapping.
private Map<Media, Integer> mediaMap;
public MediaMap()
{
mediaMap = new HashMap<>();
}
public void add(Media media)
{
mediaMap.put(media, mediaMap.getOrDefault(media, 0) + 1);
}
public void removeOneMedia(Media media)
{
if (mediaMap.containsKey(media))
{
mediaMap.put(media, mediaMap.get(media) - 1);
}
}
// And so on...
}
Without overriding the hashCode() method in the Media class, the hash based collections won't work as expected.
You can also have a look at MultiSet data structure, and use that instead.
If you are to use ArrayList then here's how its done:
// Media.java
public class Media
{
private final String support;
private final String title;
private int numberOfCopies;
public Media(Media media)
{
this(media.title, media.support, media.numberOfCopies);
}
public Media(String title, String support, int numberOfCopies)
{
this.title = title;
this.support = support;
this.numberOfCopies = numberOfCopies;
}
#Override
public int hashCode()
{
return 31 * title.hashCode() + support.hashCode();
}
#Override
public boolean equals(Object object)
{
if (object instanceof Media)
{
Media media = (Media) object;
return media.title.equals(title) &&
media.support.equals(support);
}
return false;
}
public int getNumberOfCopies()
{
return numberOfCopies;
}
public void setNumberOfCopies(int numberOfCopies)
{
this.numberOfCopies = numberOfCopies;
}
}
And here's a MediaList class which uses ArrayList:
// MediaList.java
import java.util.ArrayList;
public class MediaList
{
private ArrayList<Media> mediaList;
public MediaList()
{
mediaList = new ArrayList<>();
}
public void add(Media media)
{
set(media, +1);
}
public void remove(Media media)
{
set(media, -1);
}
private void set(Media media, int change)
{
if (change == 0)
{
return;
}
int indexOfMedia = mediaList.indexOf(media);
if (indexOfMedia != -1)
{
Media m = mediaList.get(indexOfMedia);
m.setNumberOfCopies(m.getNumberOfCopies() + change);
if (change < 0 && m.getNumberOfCopies() <= 0)
{
mediaList.remove(media);
}
}
else if (change > 0)
{
mediaList.add(media);
}
}
// And so on...
}
I have refactored your classes a little bit. I also implemented an add method. I assumed that you want to add media to the mediatheque if it is not already in the list. If it is in the list you want to add the nbex to the nbex that the item in the list has, right?
As the others I would advise you to use a HashMap() for counting if you don't need the number for your media objects.
Media.class
public class Media {
private final String support; // Format: Book, CD, DVD,etc...
private final String titre; // Title
private int nbEx; // Number of copy
public Media(String titre, String support){
this.titre = titre;
this.support = support;
this.nbEx = 1;
}
public Media(Media m){
this(m.titre, m.support);
}
public Media (){
this("", "");
nbEx = 0;
}
public boolean equals(Media m){
if (m instanceof Media){
return (this.titre.equals(m.titre) && this.support.equals(m.support));
}
return false;
}
}
Mediatheque.class
public class Mediatheque {
ArrayList<Media> contenu;
public Mediatheque(){
this.contenu = new ArrayList<Media>();
}
public Mediatheque(Mediatheque m){
this.contenu = m.contenu;
}
public boolean contains(Media m){
for(Media media: this.contenu) {
if(media.equals(m) {
return true;
}
}
return false;
}
public int indexOf(Media m){
if(this.contenu.contains(m) {
return this.contenu.indexOf(m);
}
return -1;
}
public void add(Media m){
if(this.contains(m)) {
Media media = this.contenu.get(this.contenu.indexOf(m));
media.setNbex(media.getNbex() + m.getNbex());
} else {
this.contenu.add(m);
}
}
}
Hope this helps.
I'm scratching my head as to why some code within my try statement isn't being executed. Below is the culprit code in question.
try {
Long idSociety = UtilAction.<Long>getSessionAttribute(session, idSocietyAttrName);
ContactAddressForm caf = (ContactAddressForm) form;
java.lang.System.out.println("invoiceAddresss: " + caf.getInvoiceAddress()); //This doesn't show in Console
Address address = new Address(caf.getStreet(), caf.getPostalCode(), caf.getCity(), caf.getBoitePostale());
ContactAddress ca = new ContactAddress();
ca.setInvoiceAddress(caf.getInvoiceAddress()); //Not set despite the Debugger showing the correct value for caf.
ca.setAddress(address); //But this is set 0_o?
synchronized (session) {
SocietyPeer.storeAddress(idSociety, ca);
}
addAddressesInSession(session, idSociety);
form.reset(mapping, request);
}
ContactAddress class
package fr.model.society;
import fr.model.component.Address;
public class ContactAddress {
private Long idContactAddress;
private Address address;
private Boolean invoiceAddress = false;
private Society society;
public Long getIdContactAddress() {
return idContactAddress;
}
public void setIdContactAddress(Long id) {
this.idContactAddress = id;
}
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
public void setInvoiceAddress(Boolean invoiceAddress) {
this.invoiceAddress = invoiceAddress;
}
public Boolean getInvoiceAddress() {
return invoiceAddress;
}
/**
* **************** METHODES MAPPING *****************
*/
public Society getSociety() {
return society;
}
public void setSociety(Society society) {
this.society = society;
}
public String toString() {
return getAddress().toString();
}
public boolean equals(Object o) {
if (!(o instanceof ContactAddress)) {
return false;
}
ContactAddress ca = (ContactAddress) o;
return address.equals(ca.getAddress()) && (getSociety().equals(ca.getSociety()));
}
public int hashCode() {
return ((getIdContactAddress() == null) ? 0 : getIdContactAddress().hashCode())
^ address.hashCode()
^ ((getSociety() == null) ? 0 : getSociety().hashCode());
}
}
Edit:
Essentially I'm trying to set the invoiceAddress boolean variable and for all intents and purposes I can't at the moment. Nothing is printed in the console for java.lang.System.out.println("invoiceAddresss: " + caf.getInvoiceAddress()); I also tried passing it through a temp boolean variable and that variable isn't picked up in the debugger at all.
I loaded the project in Netbeans and this issue seems to be with eclipse and the Tomcat server. Must not be updating the Warfile despite re-building.