Nullpointerexception When Creating an Array of Objects

NullPointerException when Creating an Array of objects

You created the array but didn't put anything in it, so you have an array that contains 5 elements, all of which are null. You could add

boll[0] = new ResultList();

before the line where you set boll[0].name.

Printing an object array gives null pointer exception

The reason why you get NullPointerException is because of private Student[] students=new Student[10];. It means that you have an Student array which has a fixed size of 10. Default Object values in Java is null. Without adding anything to the array it means you have 10 null objects in students.

If an offset in the students array is not filled yet, you will hit a null value and get an exception, because you try to invoke a method on null.

You can validate it in the loop:

        for(int i=0;i<students.length;i++){
            if(students[i] instanceof User) {
                System.out.println(students[i].getRollNumber());
                System.out.println(students[i].getName());
            }
        }

EDIT: This 'issue' can be avoided by using List<User> instead of User[]. But I can't decide for you if it makes more sense.

Null pointer exception for creating array of objects in java

You need to initialize the elements of your array:

Prod[] p = new Prod[3];
for(i = 0;i<3;i++)
    p[i] = new Prod(); // added this line
    // rest of code

The statement Prod[] p = new Prod[3]; just allocates space for the references to Prod objects - it doesn't create them.

Null Pointer Exception when passing an array of objects to a static method

In your createBankAccounts() method you are starting your for loop at 1, not 0. Java arrays are 0-indexed, which means they start at 0. Since your for loop starts at 1, the first element in the array never gets initialized, causing it to throw a NullPointerException.

Change this:

public static void createAccounts(Account[] bankAccounts) {
    for (int i = 1; i < bankAccounts.length; i++) {
        bankAccounts[i] = new Account(i, 100);
    }
}

To this: (int i = 1 becomes int i = 0)

public static void createAccounts(Account[] bankAccounts) {
    for (int i = 0; i < bankAccounts.length; i++) {
        bankAccounts[i] = new Account(i, 100);
    }
}

Java Object array java.lang.NullPointerException

Make it this way

public class Blocks {
public static Block[] b = new Block[8];

static {
   // Instantiating the objects present in the array
   for(int i=0; i<b.length; i++)
       b[i] = new Block();
}

public Blocks() throws IOException {
   // Now you can access them
    new Air  (b[0]);
    new Stone(b[1]);
    new Grass(b[2]);
    new Dirt (b[3]);
}

You forgot to instantiate the objects present in the array. So it is prompting null pointer exception

NullPointerException while populating an Array or a list

Because nothing is stored in array

When you do this:

    EMP[] emps = new EMP[(5)];

You just create an array with enough space to store 5 EMP, nothing inside this array.

Try:

    String[] values = {"2","4","6","8","10"};
    for(int i=0; i<emps.length; i++){
        emps[i] = new EMP();//Need to initialize object here!
        for(int j=0; j<values.length; j++){
            emps[i].setId(values[j]); 
            emps[i].setName(values[j]);
            emps[i].setDep(values[j]);
            emps[i].setSal(values[j]);
        }
    }

Note:

I think you want to do this, as calling a nested loop in the above case doesn't make any sense:

    for(int i=0; i<emps.length; i++){
        emps[i] = new EMP();//Need to initialize object here!
        emps[i].setId(values[i]); 
        emps[i].setName(values[i]);
        emps[i].setDep(values[i]);
        emps[i].setSal(values[i]);    
    }

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