CODEWITHSUNDEEP
javaobjectconstructor
J.P
J.P

Reputation: 141

where stored values from constructor in java ?

I always use constuctor only for attributes of one object. But i thin when i wrote this :

  public Predmet(int esp,int obaveze,int cena){
    this.cena=cena;
    this.obaveze=obaveze;
    this.esp=esp;

    List j = new ArrayList();
    j.add(8);
    this.nesto=(int) j.get(0);

}

where are stored this ArrayList,does it part of object,or is on stack and have reference to array in heap?

Upvotes: 1

Views: 770

Answers (3)

Brydenr
Brydenr

Reputation: 798

First, please don't use single variable names! This is bad practice and makes files harder to read. Using a more descriptive name helps to promote code readability.

The way that List j is created, it only exists in the scope of the constructor. After your constructor, List j is no longer accessible. If you wanted it to be accessible after the constructor, have a field for the object. For example:

public class Example {
    private int specialNumber;
    private List<Integer> numberList;
    /**
    * Constructs a new Example Object
    */
    public Example(int exampleNum){
        // specialNumber can be accessed from a Getter method (getSpecialNumber)
        this.specialNumber = exampleNum;
        this.numberList = new ArrayList<Integer>();
        this.numberList.add(exampleNum);
        // numberList is a field of this Example now
        List<Integer> disappearingList = new ArrayList<Integer>();
        disappearingList.add(exampleNum);
        // After this method finishes, disappearingList will be gone
    }
    // disappearingList is no longer accessible
    /**
    * Gets this Example's specialNumber value
    * @return int this.specialNumber
    */
    public int getSpecialNumber(){
        return this.specialNumber;
    }
    /**
    * Gets this Example's numberList
    * @return List<Integer> this.numberList
    */
    public List<Integer> getNumberList(){
        return this.numberList;
    }
}

There is probably a way to hook into some of the Java cleaning methods and pull it out, but that will get a little messy. If you want to be able to create an Object inside another Object, and use it after the constructor, it must be saved as a field.

Upvotes: 0

Darpan27
Darpan27

Reputation: 237

Constructor is working very similar the way methods work. At runtime, anything you define inside constructor/method are called local variables. Their scope will end as soon as execution hits the end of the constructor/method. After consturctor, your list will be eligible for GC. However, this.nesto will still get value 8 as its primitive type.

Upvotes: 0

Puce
Puce

Reputation: 38132

The ArrayList is created on the heap and only referenced by the local variable j from the stack here. After the execution of the constructor it will be eligible for garbage collection.

Upvotes: 2

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