Need to replace ArrayList with array of object

Question

I've created 'database' with ArrayList but i need to replace it with Array of object .So how can i do the change without destroying this Class?

import java.util.*;

// ArrayList to store Users.
public class Appointment {
    public static void main(String[] args) {
        String command = "";
        String date = "";
        String appointment = "";
        String time = "";
        int id = 0;
        ArrayList<User> data = new ArrayList<User>();
        Scanner input = new Scanner(System.in);
        while (!command.equalsIgnoreCase("Exit")) {
            System.out.println("Please Enter a Command or Type Exit: ");
            command = input.nextLine();
            if (command.equalsIgnoreCase("Add")) {
                System.out.print("Data: ");
                date = input.nextLine();
                System.out.print("Time: ");
                time = input.nextLine();
                System.out.println("Day of appointment:");
                day = input.nextLine();
                System.out.print("Appointment: ");
                appointment = input.nextLine();

                User validUser = new User(date, time, appointment);
                data.add(validUser);
                System.out.println("Successful!");
                System.out.println(""); //Adds an appointment to database if it's valid.
            }
        }
    }

why do you want to downgrade?everyone is upgrading from array to lists, using ArrayList is better approach — Vihar, Jun 16 '15 at 16:52
@Vihar That isn't true. ArrayLists and Arrays have different purposes, there is no "upgrade" vs. "downgrade" between these two data structures. — neuronaut, Jun 16 '15 at 16:59
possible duplicate of [From Arraylist to Array](http://stackoverflow.com/questions/7969023/from-arraylist-to-array) — Soham, Jun 16 '15 at 17:06

score 0 · Answer 1 · answered Jun 16 '15 at 16:59

0

To convert an ArrayList to an Array of that type use .toArray(). In this case, it would be

User[] users = data.toArray(new User[0]);

answered Jun 16 '15 at 16:59

JavaOG

51
4

Good find @Soham. I should have been quicker to search for duplicates rather than just answering the question. – JavaOG Jun 16 '15 at 17:34

score 0 · Answer 2 · answered Jun 18 '15 at 12:50

The only way to achive to use the arrays is to expand the array dynamically as the new 'add' command is used.

Thus, you need this method to update and expand your array;

public static User[] add(User[] userArray, User user) {
    //null array check
    if( userArray == null ) {
        userArray = new User[1];
        userArray[0] = user;

        return userArray;
    }

    User[] newArray = new User[userArray.length+1];

    int i = 0;
    for( ; i < userArray.length; i++ )
        newArray[i] = userArray[i];

    newArray[i] = user; //already incremented with post-increment operator

    return newArray;
}

And the whole test code is as follows;

import java.util.*;

// ArrayList to store Users.
public class TestAppointment {
    public static void main(String[] args) {
        String command = "";
        String date = "";
        String appointment = "";
        String time = "";
        int id = 0;
        User[] data = null;
        Scanner input = new Scanner(System.in);
        while (!command.equalsIgnoreCase("Exit")) {
            System.out.println("Please Enter a Command or Type Exit: ");
            command = input.nextLine();
            if (command.equalsIgnoreCase("Add")) {
                System.out.print("Data: ");
                date = input.nextLine();
                System.out.print("Time: ");
                time = input.nextLine();
//              System.out.println("Day of appointment:");
//              date = input.nextLine();
                System.out.print("Appointment: ");
                appointment = input.nextLine();

                User validUser = new User(date, time, appointment);
                //data.add(validUser);  // we dont need this anymore
                data = add(data, validUser);
                System.out.println("Successful!");
                System.out.println(""); // Adds an appointment to database if
                                        // it's valid.
            }
        }

        System.out.println(data.length);
        for(int i = 0; i < data.length; i++) {
            System.out.printf("%d: %s:%s:%s\n",i,data[i].getDate(),data[i].getTime(),data[i].getAppointment());
        }
    }

    public static User[] add(User[] userArray, User user) {
        //null array check
        if( userArray == null ) {
            userArray = new User[1];
            userArray[0] = user;

            return userArray;
        }

        User[] newArray = new User[userArray.length+1];

        int i = 0;
        for( ; i < userArray.length; i++ )
            newArray[i] = userArray[i];

        newArray[i] = user; //already incremented with post-increment operator

        return newArray;
    }

    private static class User {

        private String date;
        private String time;
        private String appointment;

        public User(String date, String time, String appointment) {
            this.date = date;
            this.time = time;
            this.appointment = appointment;
        }

        public String getDate() {
            return date;
        }

        public void setDate(String date) {
            this.date = date;
        }

        public String getTime() {
            return time;
        }

        public void setTime(String time) {
            this.time = time;
        }

        public String getAppointment() {
            return appointment;
        }

        public void setAppointment(String appointment) {
            this.appointment = appointment;
        }
    }

}

The output of this test code is as below;

Please Enter a Command or Type Exit: 
add
Data: testData1
Time: testTime1
Appointment: testApp1
Successful!

Please Enter a Command or Type Exit: 
add
Data: testData2
Time: testTime2
Appointment: testApp2
Successful!

Please Enter a Command or Type Exit: 
exit
2
0: testData1:testTime1:testApp1
1: testData2:testTime2:testApp2

Hope that this helps you.

Need to replace ArrayList with array of object

2 Answers2