Why arrays are needed in Java - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an array of integers named numbers.

Java

int[] [1] = new int[5];

Drag options to blanks, or click blank then click option'

Avalues

BnumList

Cnumbers

Darray

Attempts:

3 left

💡 Hint

Common Mistakes

Using a name that is not a valid Java identifier.

Forgetting to declare the array type before the name.

The array is named numbers as declared in the code.

2fill in blank

medium

Complete the code to assign the value 10 to the first element of the array.

Java

numbers[[1]] = 10;

Drag options to blanks, or click blank then click option'

A1

B0

C5

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 as the first index, which causes skipping the first element.

Using negative or out-of-bound indexes.

Array indexes in Java start at 0, so the first element is at index 0.

3fill in blank

hard

Fix the error in the code to print the length of the array.

Java

System.out.println(numbers[1]);

Drag options to blanks, or click blank then click option'

A.length

B.length()

C.size()

D.count

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses like a method call, which causes a compile error.

Using methods like size() which are for collections, not arrays.

In Java, arrays have a length property without parentheses to get their size.

4fill in blank

hard

Fill both blanks to create an array of 3 strings and assign "apple" to the first element.

Java

String[] [1] = new String[[2]];
[1][0] = "apple";

Drag options to blanks, or click blank then click option'

Afruits

B3

C5

Ditems

Attempts:

3 left

💡 Hint

Common Mistakes

Using a size that does not match the intended number of elements.

Using inconsistent names for the array variable.

The array is named fruits and has size 3, so new String[3].

5fill in blank

hard

Fill all three blanks to create an array of integers, assign 5 to the second element, and print it.

Java

int[] [1] = new int[[2]];
[1][1] = [3];
System.out.println([1][1]);

Drag options to blanks, or click blank then click option'

Ascores

B4

C5

Dvalues

Attempts:

3 left

💡 Hint

Common Mistakes

Using an index out of bounds for the array size.

Assigning a value to an invalid index.

The array scores has size 4, the second element (index 1) is assigned 5, and then printed.

Practice

1. Why do we need arrays in Java?

easy

A. To store only one value at a time

B. To store multiple values of the same type together

C. To perform mathematical calculations automatically

D. To create graphical user interfaces

Solution

1. Step 1: Understand the purpose of arrays

   Arrays group many values of the same type in one place for easy handling.

2. Step 2: Compare options with array purpose

   Only To store multiple values of the same type together correctly describes storing multiple values together.

3. Final Answer:

   To store multiple values of the same type together -> Option B

4. Quick Check:

   Arrays store many values [OK]

Hint: Arrays hold many same-type values together [OK]

Common Mistakes:

• Thinking arrays store different types together
• Confusing arrays with single variables
• Assuming arrays perform calculations automatically

2. Which of the following is the correct way to declare an array of integers in Java?

easy

A. numbers int[];

B. array int numbers;

C. int numbers[] = new array;

D. int[] numbers;

Solution

1. Step 1: Recall Java array declaration syntax

   Java arrays are declared as type followed by square brackets, then variable name.

2. Step 2: Check each option's syntax

   Only int[] numbers; matches correct syntax: int[] numbers;

3. Final Answer:

   int[] numbers; -> Option D

4. Quick Check:

   Correct Java array syntax [OK]

Hint: Type[] name; is correct array declaration [OK]

Common Mistakes:

• Using 'array' keyword which doesn't exist
• Placing brackets after variable name incorrectly
• Mixing order of type and variable

3. What will be the output of this Java code?

int[] arr = {10, 20, 30};
System.out.println(arr[1]);

medium

A. 10

B. 30

C. 20

D. ArrayIndexOutOfBoundsException

Solution

1. Step 1: Identify array elements and indexes

   Array arr has elements: arr[0]=10, arr[1]=20, arr[2]=30.

2. Step 2: Find value at index 1

   arr[1] is 20, so printing arr[1] outputs 20.

3. Final Answer:

   20 -> Option C

4. Quick Check:

   arr[1] = 20 [OK]

Hint: Array index starts at 0, so arr[1] is second element [OK]

Common Mistakes:

• Confusing index 1 with first element
• Expecting output 10 instead of 20
• Thinking array indexes start at 1

4. Find the error in this Java code snippet:

int[] nums = new int[3];
nums[3] = 5;

medium

A. Index 3 is out of bounds for array of size 3

B. Array size must be declared as 5

C. Array cannot store integers

D. Missing semicolon after array declaration

Solution

1. Step 1: Understand array size and valid indexes

   Array nums has size 3, so valid indexes are 0, 1, and 2.

2. Step 2: Check the index used in assignment

   nums[3] tries to access fourth element, which is invalid and causes error.

3. Final Answer:

   Index 3 is out of bounds for array of size 3 -> Option A

4. Quick Check:

   Array indexes go 0 to size-1 [OK]

Hint: Array indexes start at 0, max index = size-1 [OK]

Common Mistakes:

• Using index equal to array size
• Thinking array indexes start at 1
• Assuming array size can change automatically

5. You want to store the names of 5 students and print the third student's name. Which approach is best in Java?

hard

A. Use an array of Strings with size 5

B. Use 5 separate String variables for each name

C. Use a single String variable with all names concatenated

D. Use an integer array to store names

Solution

1. Step 1: Identify the need to store multiple related values

   We need to store 5 names, which are multiple values of the same type (String).

2. Step 2: Choose the best data structure for multiple same-type values

   An array of Strings with size 5 efficiently stores and accesses each name by position.

3. Step 3: Access the third student's name

   Using array index 2 (third element) allows easy retrieval.

4. Final Answer:

   Use an array of Strings with size 5 -> Option A

5. Quick Check:

   Arrays store multiple same-type values [OK]

Hint: Use array to store multiple same-type items for easy access [OK]

Common Mistakes:

• Using separate variables makes code long and hard to manage
• Concatenating names loses individual access
• Using integer array for Strings is invalid