Java - How to access an ArrayList of another class

Question

Hello I m a beginner in Java and this is my question  I have this first class with the following variables   import java util ArrayList   public class numbers       private int number1   50      private int number2   100      And I have this class too   import java util ArrayList   public class test       private numbers number      My question here is  I want to store the number1  amp  number2 variables into an ArrayList  then access this ArrayList from class test  How can I do that

User · Answer

Two ways  1 instantiate the  first class and getter for arrayList   or  2 Make arraylist as  static  And  finally   Java Basics By Oracle

User · Answer

import java util ArrayList  public class numbers      private int number1   50     private int number2   100     private List lt Integer gt  list      public numbers            list   new ArrayList lt Integer gt            list add number1          list add number2            public List lt Integer gt  getList            return list           And the test class   import java util ArrayList  public class test      private numbers number        example    public test          number   new numbers         List lt Integer gt  list   number getList           hurray

User · Answer

Put them in an arrayList in your first class like   import java util ArrayList      public class numbers        private int number1   50      private int number2   100       public ArrayList lt int gt  getNumberList             ArrayList lt int gt  numbersList  new ArrayList lt int gt             numbersList add number1           numberList add number2                        return numberList            Then  in your test class you can call numbers getNumberList   to get your arrayList  In addition  you might want to create methods like addToList   removeFromList in your numbers class so you can handle it the way you need it   You can also access a variable declared in one class from another simply like  numbers numberList    if you have it declared there as public   But it isn t such a good practice in my opinion  since you probably need to modify this list in your code later    Note that you have to add your class to the import list   If you can tell me what your app requirements are  i ll be able tell you more precise what i think it s best to do

User · Answer

You can do the following     public class Numbers       private int number1   50      private int number2   100      private List lt Integer gt  list       public Numbers           list   new ArrayList lt Integer gt           list add number1         list add number2              int getNumber int pos              return list get pos                public class Test       private Numbers numbers       public Test          numbers   new Numbers          int number1   numbers getNumber 0         int number2   numbers getNumber 1

User · Answer

You can do this by providing in class numbers    A method that returns the ArrayList object itself   A method that returns a non-modifiable wrapper of the ArrayList  This prevents modification to the list without the knowledge of the class numbers   Methods that provide the set of operations you want to support from class numbers  This allows class numbers to control the set of operations supported    By the way  there is a strong convention that Java class names are uppercased    Case 1  simple getter    public class Numbers         private List lt Integer gt  list        public List lt Integer gt  getList     return list                  Case 2  non-modifiable wrapper     public class Numbers         private List lt Integer gt  list        public List lt Integer gt  getList     return Collections unmodifiableList  list                    Case 3  specific methods     public class Numbers         private List lt Integer gt  list        public void addToList  int i     list add i           public int getValueAtIndex  int index     return list get  index

[java] Java - How to access an ArrayList of another class?

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