为什么我的 showAllUsers() 方法不使用每个对象的正确格式标题打印出用户列表？

Question

I have a program that that stores user objects into an array. There are two types of users (Customers, Employees) that both extend from user class. When I run the method below in main it does not give the correct header format for each object. Each extended class has its own unique header and share the getFormattedHeader() method. I thought that if i print out the array list that each time the object.getFormattedHeader() is called, it would give that objects specific header. How can I go through the array and if it prints out a certain object, it prints out its unique header?

public void showAllUsers() {
    System.out.println(hardwareStore.getAllUsersFormatted());
}

User.java

package hardwarestore;

import java.io.Serializable; import java.util.ArrayList;

public abstract class User implements Serializable {

    /**      *       */     private static final long serialVersionUID = 1L;

    private final int id;   private final String firstName;     private final String lastName;      public User(int id, String firstName, String lastName) {        this.id = id;       this.firstName = firstName;         this.lastName = lastName;   }       public abstract String getFormattedInfo(User user);     public abstract String getFormattedHeader();    public abstract ArrayList<Item> readDB(ArrayList<Item> items);

    public int getId() {        return id;  }

    public String getFirstName() {      return firstName;   }

    public String getLastName() {       return lastName;    }
         }

Employee.java

package hardwarestore;

import java.util.ArrayList;

public class Employee extends User{
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private final int socialNumber;
    private final float salary;

    public Employee(int id, String firstName, String lastName, int socialNumber, float salary) {
        super(id, firstName, lastName);
        this.socialNumber = socialNumber;
        this.salary = salary;
    }

    public int getSocialNumber() {
        return socialNumber;
    }

    public float getSalary() {
        return salary;
    }

    @Override
    public String getFormattedInfo(User user) {
        String text = String.format("| %-10s| %-25s| %-25s| %-20s| %-10s|%n", Integer.toString(user.getId()),
                user.getFirstName(), user.getLastName(),((Employee)user).getSocialNumber(),String.format("%.2f", ((Employee)user).getSalary()));
    text += " ------------------------------------------------------------------------------------\n";

    return text;
    }

    @Override
    public String getFormattedHeader() {
         String text = " ------------------------------------------------------------------------------------\n" +
                    String.format("| %-10s| %-25s| %-25s| %-20s| %-10s|%n", "ID Number", "First Name", "Last Name","Social Security", "Salary") +
                          " ------------------------------------------------------------------------------------\n";

         return text;
    }

    @Override
    public ArrayList<Item> readDB(ArrayList<Item> items) {
        // TODO Auto-generated method stub
        return null;
    }
}

Customer.java

package hardwarestore;

import java.util.ArrayList;

public class Customer extends User {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private final String phoneNumber;
    private final String address;


    public Customer(int id, String firstName, String lastName, String phoneNumber, String address) {
        super(id, firstName, lastName);
        this.phoneNumber = phoneNumber;
        this.address = address;
    }


    public String getPhoneNumber() {
        return phoneNumber;
    }


    public String getAddress() {
        return address;
    }


    @Override
    public String getFormattedInfo(User user) {
        String text = String.format("| %-10s| %-25s| %-25s| %-20s| %-10s|%n", Integer.toString(user.getId()),
                user.getFirstName(), user.getLastName(),((Customer)user).getPhoneNumber(), ((Customer)user).getAddress());
    text += " ------------------------------------------------------------------------------------\n";

    return text;
    }


    @Override
    public String getFormattedHeader() {
         String text = " ------------------------------------------------------------------------------------\n" +
                    String.format("| %-10s| %-25s| %-25s| %-20s| %-10s|%n", "ID Number", "First Name", "Last Name","Phone Number", "Address") +
                          " ------------------------------------------------------------------------------------\n";

         return text;
    }


    @Override
    public ArrayList<Item> readDB(ArrayList<Item> items) {
        // TODO Auto-generated method stub
        return null;
    }


}

Methods that suppose to list all users formatted by their customized formatting.

/**
     * method getAllUsersFormatted returns the current list of users in the 
     * Arraylist.
     * 
     * @return a formatted String representation of all the users in userList.
     */
    public String getAllUsersFormatted() {
        return getFormattedUserList(userList);
    }

    private String getFormattedUserList(ArrayList<User> users) {
        String text = users.get(0).getFormattedHeader();
        for(int i = 0; i<users.size(); i++) {
            text += users.get(i).getFormattedInfo(users.get(i));
        }
        return text;
    }

output:

The output gives the header for the employee and not the customer.

Answer 1

You can group the list of users according to their type and print the header only once for a type ( Customer or Employee )

List<User> list = ...
Map<Class<? extends User>, List<User>> groupedResult = list.stream()
        .collect(Collectors.groupingBy(e -> e.getClass()));
groupedResult
        .entrySet()
        .forEach(entry -> {
 //print the header for the object of the current class type
             entry.getValue()
                  .stream()
                  .findFirst()
                  .ifPresent(user -> user.getFormattedHeader());

           //print the data
            entry.getValue()
                 .forEach(user -> user.getFormattedInfo(user));
        });

Also, there is no need to send the user instance to getFormattedInfo as the method is called on the user object ( users.get(i).getFormattedInfo ) and you can access these instance variables directly You can change getFormattedInfo as

@Override
    public String getFormattedInfo(User user) {
        String text = String.format("| %-10s| %-25s| %-25s| %-20s| %-10s|%n", Integer.toString(getId()),
                getFirstName(), getLastName(), getPhoneNumber(), getAddress());
    text += " ------------------------------------------------------------------------------------\n";
    return text;
    }