To refer to ArrayList, which is declared in List method in java?

Question

Model:

@Entity(name= "User")
@Table(name= "Registration")
public class User {

private int id;
private String orderNo;
private String productName;
private BigDecimal price;
private Integer qty;
private Boolean editable;

public User(){
}

public User(int id, String orderNo, String productName, BigDecimal price, Integer qty){
     this.id= id;
     this.orderNo= orderNo;
     this.productName= productName;
     this.price= price;
     this.qty= qty;
 }

public int getId() {
    return id;
}
public void setId(int id) {
    this.id = id;
}
public String getOrderNo() {
    return orderNo;
}
public void setOrderNo(String orderNo) {
    this.orderNo = orderNo;
}
public String getProductName() {
    return productName;
}
public void setProductName(String productName) {
    this.productName = productName;
}
public BigDecimal getPrice() {
    return price;
}
public void setPrice(BigDecimal price) {
    this.price = price;
}
public Integer getQty() {
    return qty;
}
public void setQty(Integer qty) {
    this.qty = qty;
}
    public Boolean getEditable() {
    return editable;
}

    public void setEditable(Boolean editable) {
        this.editable = editable;
    }
}

Dao metod:

public class UserDao implements UserInterface{

    private static final Logger logger= LoggerFactory.getLogger(UserDao.class);

               Session session= HibernateUtil.getSessionFactory().openSession();

               public void save(User newUser){
                 //  Session session= HibernateUtil.getSessionFactory().openSession();
                   session.beginTransaction();
                   session.save(newUser);
                   session.getTransaction().commit();
                   session.close();
               }


               @SuppressWarnings("unchecked")
               public Integer getId() {
                   String hql = "SELECT MAX (user.id) FROM User user";
                   Query<Integer> query = session.createQuery(hql);
                   List<Integer> results = query.list();
                   Integer userId = 1;

                   if(results.get(0)!= null) {
                       userId= results.get(0)+ 1;
                   }

                   return userId;
               }

            @SuppressWarnings("unchecked")
            @Override
            public List<User> listUsers() {
                // TODO Auto-generated method stub
                Session session= HibernateUtil.getSessionFactory().openSession();
                List<User> userList= session.createQuery("FROM User").list();
                 for(User u: userList){
                     logger.info("Users list:: "+ u);
                 }
                return userList;
            }
}

Managed Bean:

@ManagedBean(name= "myBean", eager= true)
@RequestScoped
public class UserDrivingBean {

    private String orderNo;
    private String productName;
    private BigDecimal price;
    private Integer qty;

    List<User> users;

    public List<User> getUsers() {
        return users;
    }

    public void setUsers(List<User> users) {
        this.users = users;
    }

    public String saveUser(){
        UserDao userDao= new UserDao();
        Integer userId= userDao.getId();
        User user= new User(userId, orderNo, productName, price, qty);
        userDao.save(user);
        System.out.println("User successfully saved!");
        return "output";
    }

    public void addUser(){
        UserDao userDao= new UserDao();
        Integer userId= userDao.getId();
        User newUser= new User(userId, orderNo, productName, price, qty);
        newUser.setEditable(true);
        userDao.addCustomer(newUser);
    }

    public void plusNewUser(){
        UserDao daoObj= new UserDao();
        List<User> users= getAllUsers();
        Integer userId= daoObj.getId();
        User addUser= new User();
        addUser.setEditable(true);
        users.add(addUser);
    }

    public List<User> getAllUsers(){
        users= new ArrayList<>();
        UserDao daoObj= new UserDao();
        users= daoObj.listUsers();
    /*  Integer userId= daoObj.getId();
        User addUser= new User(userId, orderNo, productName, price, qty);
        addUser.setEditable(true);
        users.add(addUser); */ //!!!This works, when added directly to method!
        return users;
    }

    public String getOrderNo() {
        return orderNo;
    }
    public void setOrderNo(String orderNo) {
        this.orderNo = orderNo;
    }
    public String getProductName() {
        return productName;
    }
    public void setProductName(String productName) {
        this.productName = productName;
    }
    public BigDecimal getPrice() {
        return price;
    }
    public void setPrice(BigDecimal price) {
        this.price = price;
    }
    public Integer getQty() {
        return qty;
    }
    public void setQty(Integer qty) {
        this.qty = qty;
    }

xhtml page:

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
      xmlns:h="http://xmlns.jcp.org/jsf/html"      
      xmlns:f="http://xmlns.jcp.org/jsf/core">
<h:head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Retreiving func.</title>
</h:head>
<h:body>
 <f:view>
 <h:form id="adminInf">
 <center>
  <h:dataTable border="1" id="table" var="y" value="#{myBean.allUsers}">
   <h:column>
    <f:facet name="header">
     <h:outputLabel value="Id: "/>
    </f:facet>
    <h:outputText value="#{y.id}"/>
   </h:column>
   <h:column>
    <f:facet name="header">
     <h:outputLabel value="Order No: "/>
    </f:facet>
    <h:inputText value="#{y.orderNo}" rendered="#{y.editable}"></h:inputText>
    <h:outputText value="#{y.orderNo}" rendered="#{!y.editable}"/>
   </h:column>
   <h:column>
    <f:facet name="header">
     <h:outputLabel value="Product: "/>
    </f:facet>
    <h:inputText value="#{y.productName}" rendered="#{y.editable}"></h:inputText>
    <h:outputText value="#{y.productName}" rendered="#{!y.editable}"/>
   </h:column>
   <h:column>
    <f:facet name="header">
     <h:outputLabel value="Price: "/>
    </f:facet>
    <h:inputText value="#{y.price}" rendered="#{y.editable}"></h:inputText>
    <h:outputText value="#{y.price}" rendered="#{!y.editable}"/>
   </h:column>
   <h:column>
    <f:facet name="header">
     <h:outputLabel value="Quantity: "/>
    </f:facet>
    <h:inputText value="#{y.qty}" rendered="#{y.editable}"></h:inputText>
    <h:outputLabel value="#{y.qty}" rendered="#{!y.editable}"/>
   </h:column>

   <h:column id="insertBtn">
    <h:commandButton value="Insert" action="#{myBean.addUser}" rendered="#{y.editable}">
     <f:ajax execute="@form" render="@form"/>
    </h:commandButton>
   </h:column>
  </h:dataTable>
  <h:commandButton value="AddNew" action="#{myBean.plusNewUser}" update="table"/>
  <h:commandLink value="Home" action="input"/>
 </center>
 </h:form>
 </f:view>
</h:body>
</html>

Is it possible to refer to List<User> users= new ArrayList<>(); from another method, which declared in public List getAllUsers(){} method to be able to add new objects in it? for example:

    public void addNewUser(){
        User addUser= new User(userId, orderNo, productName, price, qty);//Create new object
        addUser.setEditable(true);// Open new iput fields(<h:inputText>)on xhtml page
        users.add(addUser);//refer to ArrayList from getAllUsers() method and add new object in it(new User).
}

With this method I retreive data from DB into xhtml page:

public List<User> getAllUsers(){
    List<User> users= new ArrayList<>();
    UserDao daoObj= new UserDao();
    users= daoObj.listUsers();
    return users;
}

Answer 1

yes it is possible with java generics concept.

List<User> users= new ArrayList<User>();



public class SomeClass {


List<User> users= new ArrayList<User>();
    public List<User> getAllUsers(){
        // here just use the global variable, no need to add List<User> again
         users = new ArrayList<>();
        UserDao daoObj = new UserDao();
        users = daoObj.listUsers();
        return users;
    }

    public void addNewUser() {
         users = getAllUsers();
        User addUser = new User(userId, orderNo, productName, price, qty);//Create new object
        addUser.setEditable(true);// Open new input fields(<h:inputText>)on xhtml page
        users.add(addUser);//refer to ArrayList from getAllUsers() method and add new object in it(new User).

        // save user to DOA, depend on how you create your DAO, it maybe something like
        UserDao daoObj = new UserDao();
        daoObj.insertUser(addUser);
    }
}

Answer 2

I believe what you want to do is get List<User> users = new ArrayList<>(); which is exist in public List<User> getAllUsers() method from another method like in public void addNewUser() .

The answer to question above is No you can't , unless you change something in your code.

EDIT

you can create it like this if you want to keep the local declaration.

public class SomeClass {

    public List<User> getAllUsers(){
        // here just use the global variable, no need to add List<User> again
        List<User> users = new ArrayList<>();
        UserDao daoObj = new UserDao();
        users = daoObj.listUsers();
        return users;
    }

    public void addNewUser() {
        List<User> users = getAllUsers();
        User addUser = new User(userId, orderNo, productName, price, qty);//Create new object
        addUser.setEditable(true);// Open new input fields(<h:inputText>)on xhtml page
        users.add(addUser);//refer to ArrayList from getAllUsers() method and add new object in it(new User).

        // save user to DOA, depend on how you create your DAO, it maybe something like
        UserDao daoObj = new UserDao();
        daoObj.insertUser(addUser);
    }
}

And have you save the users to DAO after add new user?