CODEWITHSUNDEEP
javaarraysobjectconstructor
Echo
Echo

Reputation: 305

Java | acessing object variables from inside constructor?

I don't normally use Java and I'm currently trying to help a friend out with a java assignment and this has me stuck

I'm trying to access an array that I create in the constructor of an Object but I cannot figure out how to access it.

public class ADTbag {
   String item = "Testing";


   public ADTbag(int size) {
      // This constructor has one parameter, name.
      String[] bag = new String[size];

      bag[0] = Integer.toString(size);
      System.out.println("A bag was created with the size of " + size + " | " + bag[0]);
   }

   public void insert() {
      /* Insert an item */
      /* One Problem this public void doesn't have access to the bag var"
      System.out.println(bag);

   }

I feel like this is a simple concept in java but I cannot find anything on my googles that has helped me. I want to be able to insert something in the bag or string array object using the insert method. So something like this.

public static void main(String []args) {
      /* Object creation */
      ADTbag myBag = new ADTbag(5);

      String value = "Some Value";
      /* I want to do this */
      mybag.insert(value);


   }
}

Upvotes: 1

Views: 103

Answers (3)

Lucas Sousa
Lucas Sousa

Reputation: 352

First of all you have to make the bag field something global. After that we can create a function to insert/add a new element to your bags. Then is not necessary work with constructor, as you're trying to do.

Another thing is, as you're talking about inserting and/or adding itens to a "list", is adequated use ArrayList instead a standard array.

ArrayList is a data/collection structure that ables you to add, remove, set, get (and some other operations) at runtime above the same object. If we want to insert a new item inside a array we can't; for this we have to create another array with size+1 and after set all elements of the new array. Then this is so confusing for a simple operation.

Thinking in this I'll give you a approach that uses this, take a look:

import java.util.ArrayList;

public class ADTbag {
    /*
    global field to be referenced through entire class.
    We have to specify the type of objects that will be inserted
    inside this list, in this case String
     */
    ArrayList<String> bag;

    String item = "Testing";

    //constructor doesn't need parameter
    public ADTbag() {
        //here we init the bag list
        bag = new ArrayList();

        //adds your "standard item" on creating
        bag.add(item);



      /*
        prints your msg.

        - to get the size of a ArrayList just call list.size();
        - to get the item from the X index just call list.get(X)
         */
        System.out.println("A bag was created with the size of " + bag.size() + " | " + bag.get(0));
    }

    /*
    you doesn't need a new method
     */
}

To use do this:

public static void main(String[] args) {
    ADTbag myBag = new ADTbag();
    myBag.bag.add("some value");
}

Upvotes: 0

Rmahajan
Rmahajan

Reputation: 1361

Define variable as instance variables

public class ADTbag {
       String item = "Testing";
       String[] bag;

       public ADTbag(int size) {
          // This constructor has one parameter, name.
         this.bag = new String[size];

          bag[0] = Integer.toString(size);
          System.okaut.println("A bag was created with the size of " + size + " | " + bag[0]);
       }

       public void insert() {
          /* Insert an item */
          /* One Problem this public void doesn't have access to the bag var"
          System.out.println(bag);*/

       }
}

Which will look like above.

Upvotes: 0

Kai
Kai

Reputation: 2599

You need to make bag a class member so it is accessible outside of the constructor.

Upvotes: 1

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