Core Java - Interview Questions and Answers for 'Array' | Search Interview Question

Core Java - Interview Questions and Answers for 'Array' - 69 question(s) found - Order By Rating

Q1. How can we create an arraylist of unique values ?

Core Java

Ans. We can put the value in a set to enforce uniqueness and then dum those value into an arraylist.

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Q2. Write a program to make an array act as a set.

Core Java

Ans. public Set convertArrayToList(T array[]) {
Set set = new HashSet<>(Arrays.asList(array));
return set;
}

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Q3. Difference between ArrayList and HashSet ?

Core Java

Ans. ArrayList is a list , i.e an implementation of List interface whereas HashSet is a Set and an implementation of Set interface.

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Q4. difference between ArrayList and array ?

Core Java

Ans. ArrayList is a variable length collection class whereas arrays are fixed length primitive structure.

We can use generics with arraylist but not with arrays.

We can store primitive data types within arrays but can't with ArrayList. In ArrayList that needs to be converted to Wrapper objects.

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Q5. Difference between List and ArrayList ?

Core Java

Ans. List is an interface whereas ArrayList is an implementation of List.

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Q6. Write a Program to Find the maximum sum of the sub array ?

Data Structure

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Q7. Why doesn't this code give compile time error when we are clearly trying to add an integer element to an array of Strings

Object[] strArray = new String[2];
strArray[0] = 5;

Core Java

Ans. Because the reference is of Object Array and the resolution of what it holds is identified at the runtime.

String[] strArray = new String[2];
strArray[0] = 5;

would have given the compile time array as the reference is of String array.

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Q8. Will this give compile time error ?

Object[] strArray = new String[2];
strArray[0] = 5;

Core Java

Ans. No. But It will throw ArrayStoreException at runtime.

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Q9. What is the problem with this code

String[] strArray = new String[2];
strArray[0] = 5;

Core Java

Ans. We are trying to add an integer element to an array of String. Will give compile time error.

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Q10. If arrays cannot be resized , Why is this code valid

String[] strArray = new String[2];
strArray = new String[5];

Core Java

Ans. We are not resizing the first array here but assigning the reference strArray to a new Array with size 5.

So after line 2, We have 2 arrays in memory, one with size 2 and other with size 5 with strArray referring to second array with size 5.

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Q11. Is this code valid

String[] strArray = new String[2];
strArray.length = 5;

Core Java

Ans. It will give compile time error saying "The final field array.length cannot be assigned"

Arrays once initialized cannot be resized.

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Q12. Is this array initialization correct ? If Yes, What will be the size of array ?

String[] strArray = new String[3]{"Buggy","Bread"};

Core Java

Ans. No. It will result in error saying "Cannot define dimension expressions when an array initializer is provided"

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Q13. Is this array initialization correct ? If Yes, What will be the size of array ?

String[] strArray = new String[]{"Buggy","Bread"};

Core Java

Ans. Yes, size of the array will be 2.

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Q14. Is this array declaration correct ? If not , Why ?

String[] strArray = new String[];

Core Java

Ans. No, We haven't specified the size of array to be initialized.

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Q15. Can we make array volatile in Java ?

Core Java

Ans. Yes, you can make an array (both primitive and reference type array e.g. an int array and String array) volatile in Java but only changes to reference pointing to an array will be visible to all threads, not the whole array

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Q16. Can we have 3 dimensional arrays in Java ?

Core Java

Ans. Yes

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Q17. Can we declare an array without assigning the size of an array?

Core Java

Ans. No, It will throw compile time error saying "must provide either dimension expressions or an array initializer"

Alternatively we can provide array initializer like

String[] strArray = new String[]{"Buggy","Bread"};

which will initialize it to size 2 with values as "Buggy" and "Bread"

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Q18. Difference between Arrays and LinkedList ?

Data Structure

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Q19. Difference between Arrays and ArrayList ?

Core Java

Ans. Both Arrays and ArrayLists are used to store elements. Elements can be either primitives or objects in case of Arrays, but only objects can be stored in Arraylist. Array is a fixed length data structure while arraylist is variable length collection class. Once created, you cannot change the size of the arrays, but arraylists can dynamically resize itself when needed.Another notable difference between Arrays and Arrayslist is that arary is part of core java programming and array list is part of collection classes

Sample Code for arrays arraylist

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Q20. What is the time and space complexity for different operations for arrays ?

Core Java

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Q21. Are arrays Thread Safe ?

Core Java

Ans. Yes

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Q22. How can we check equality for Arrays in Java ?

Core Java

Ans. You call the method java.util.Arrays.equals(Object[] a, Object[] a2)?

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Q23. Are Arrays treated like primitives or like objects in Java ?

Core Java

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Q24. What are jagged arrays ?

Core Java

Ans. an array of different sizes

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Q25. What is an anonymous array in Java ?

Core Java

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Q26. What is ArrayStoreException ?

Core Java

Ans. It's an exception that is thrown when we attempt to add value of an incompatible type to an array.

For example -

Object[] strArray = new String[2];
strArray[0] = 5;

In this code, strArray reference of type Object has currently been assigned the String array but at line 2 we are trying to add an integer value.

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Q27. Can we change the size of array once created ?

Core Java

Ans. No. Arrays cannot resize dynamically.

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Q28. How arrays work internally ?

Core Java

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Q29. Write code to sort an array.

Algorithm

Ans. https://www.geeksforgeeks.org/arrays-sort-in-java-with-examples/

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Q30. Find Intersection/union between two arrays.

Core Java

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