CODEWITHSUNDEEP
javaarraysarraylist
Armon Gorgani
Armon Gorgani

Reputation: 41

How to use a method in java to store information from an arraylist

For a project that i am doing, i would like to use a separate class to store information of various people in an arraylist. in this case, the method will contain an arraylist of strings to store all my information. when i tried doing this i realized that every time i run the storage to add a string to the arraylist, it gets rid of all previous info from the arraylist.

is it possible to make it so both the Strings Hello, How Are You? and I'm fine. How Are You? add to the array in class two without having the array reset once the method is rerun?

public class one
{
    public static void main (String [] args)
    {
        two t = new two();

        t.storage("Hello, How Are You?");
        t.storage("I'm fine. How Are You?");
    }
}
import java.util.ArrayList;
public class two
{
    public static void storage(String toBeAdded)
    {
        ArrayList<String> al = new ArrayList<String>();

        al.add(toBeAdded);
        System.out.println(al);
    }
}

Given Output:

[Hello, How Are You?] [I'm fine. How Are You?]

Expected Output:

[Hello, How Are You?] [Hello, How Are You?, I'm fine. How Are You?]

Upvotes: 3

Views: 1876

Answers (4)

Oghli
Oghli

Reputation: 2351

in your class two the problem in the method storage your logic isn't right every time you call storage to save new string you create new arraylist al which will erase all previous information in the old arraylist.

to solve that define static arraylist in class two and add information to it by method storage:

public class two
{
  public static ArrayList<String> al = new ArrayList<String>();

    public void storage(String toBeAdded)
    {
        al.add(toBeAdded);
        System.out.println(al);
    }
}

Note : also storage method shouldn't be static method because you are creating object of class two and calling the method through this object so if you try to test it it will give you warning:

access static method storage

reason of warning that you are trying to access static method storage in your object t of class two.

when you declare static method in class the right way to call it:

ClassName.MethodName()

in your example:

two.storage("Hello, How Are You?");
two.storage("I'm fine. How Are You?");

Upvotes: 0

Vasu
Vasu

Reputation: 22452

There are two options to solve your problem:

Option(1): Your current ArrayList scope is local to the storage method because you are creating a brand new ArrayList on each call (to storage() method), but what you need is a static ArrayList object at class level as shown below, but because you are invoking storage() method using an object, this is not preferable option (explained below clearly) and compiler is already throwing a warning and you are ignoring it.

public class two {

    private static ArrayList<String> al = new ArrayList<String>();

    public static void storage(String toBeAdded)
    {
        al.add(toBeAdded);
        System.out.println(al);
    }
}

Option(2) (Prefer this): Remove the static scope and declare ArrayList<String> as an instance variable as shown below (prefer this option) because you are calling a static method using an object reference which is not required and creates confusion. 

public class two {

        private ArrayList<String> al = new ArrayList<String>();

        public void storage(String toBeAdded)
        {
            al.add(toBeAdded);
            System.out.println(al);
        }
    }

Always ensure that static variables/methods are invoked using classname (like Two.storage()) without creating any object because they are class level members i.e., they are not meant for a single object. I strongly suggest you read this and understand this subject more clearly.

Apart from above important point, always ensure that you follow the Java naming standards like class names should start with uppercase which you are violating.

Upvotes: 2

asad_hussain
asad_hussain

Reputation: 2011

Your mistake

Each time you are calling storage() method,you are creating a new object of 'ArrayList'.

Solution

So,make an object of class two and pass it alongwith the string to the method storage()

import java.util.ArrayList;
    public class one
    {
        public static void main (String [] args)
        {
            two t = new two();

            t.storage(t,"Hello, How Are You?");
            t.storage(t,"I'm fine. How Are You?");
        }
    }

     class two
    {
         ArrayList<String> al = new ArrayList<String>();
        public static void storage(two object,String toBeAdded)
        {


            object.al.add(toBeAdded);
            System.out.println(object.al);
        }
    }

Upvotes: 1

stinepike
stinepike

Reputation: 54742

Instead of declaring the ArrayList as local variable, use it as a field. Also make the method non-static

public class two
{

    private ArrayList<String> al = new ArrayList<String>();
    public void storage(String toBeAdded)
    {

        al.add(toBeAdded);
        System.out.println(al);
    }
}

Upvotes: 2

Related Questions