CODEWITHSUNDEEP
java
Marwadi
Marwadi

Reputation: 151

How is the memory allocated(stack and heap reference) when an OBJECT array is created?

like 

public static student[] arr = new student[10];

now, student is a class with some instance variables name(String) and age(int). I wanna know that as soon as this line is executed what will happen?? Will all the ten references get memory or I have to allocate them individually?? What if tried to access student[5].age? I need to know the memory allocation status.. Thank You...............

Upvotes: 2

Views: 1502

Answers (5)

Sorter
Sorter

Reputation: 10240

Only reference variables will be created, when you create an array of objects. In your case reference variables for student class.

In the following image, a set of reference variables are created. Then, you can point those reference variables to actual objects, later.

Dog object array

Upvotes: 2

ata
ata

Reputation: 9011

When the above statement is executed, JVM will create 10 contiguous memory location, each big enough to hold reference to student. This array, however, will contain no references or null if you will. When you execute statement like arr[0] = new student(); a student object will be created on heap and its reference will be saved in arr[0]. Remember that the array is also allocated on heap.

So once you have create 10 student objects, each will be allocated somewhere on the heap but their references will be stored in arr

Upvotes: 3

Prabhakaran Ramaswamy
Prabhakaran Ramaswamy

Reputation: 26084

public static student[] arr = new student[10]; will allocate the memory for 10 students. These memory are filled with null.

So here you cant access student[5].age because the reference to the actual object doesn't exist.

We need to create the Object reference individually like below

 for(int i=0;i<10;i++){
   student[i]= new Student();
 }

if you are accessing student[5].age before creating the actual object reference you will end with NullPointerException.

Upvotes: 1

NPE
NPE

Reputation: 500963

Will all the ten references get memory or I have to allocate then individually?

You will get space for ten references. Those references will be initialized to null. If you want them set to anything other than null, you'll have to do it separately.

Upvotes: 0

Suresh Atta
Suresh Atta

Reputation: 122026

Yes 

public static student[] = new student[10];

As soon as that line executes ,JVM allocates memory for 10 student references.

From official docs on Arrays, look at the flow.

  // declares an array of integers
        int[] anArray;

        // allocates memory for 10 integers
        anArray = new int[10];

        // initialize first element
        anArray[0] = 100;

Upvotes: 2

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