Array Declaration and Initialization in DSA Java - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an integer array named numbers with size 5.

DSA Java

int[] numbers = new int[[1]];

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

A0

B10

C1

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using zero or negative numbers for array size.

Forgetting to specify the size inside the brackets.

The array size must be 5 to hold five elements.

2fill in blank

medium

Complete the code to declare and initialize an array of strings with values "apple", "banana", and "cherry".

DSA Java

String[] fruits = [1];

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

Anew String[] {"apple", "banana", "cherry"}

Bnew String[] ("apple", "banana", "cherry")

CString[] {"apple", "banana", "cherry"}

Dnew String(3) {"apple", "banana", "cherry"}

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of curly braces for initialization.

Omitting the new keyword.

The correct syntax to initialize an array with values uses new String[] and curly braces.

3fill in blank

hard

Fix the error in the code to correctly declare an array of doubles named scores with size 4.

DSA Java

double[] scores = new double[1];

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

A(4)

B{4}

C[4]

D<4>

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of square brackets.

Using curly braces or angle brackets which are invalid here.

Array size must be specified inside square brackets [].

4fill in blank

hard

Fill both blanks to declare and initialize an integer array named primes with values 2, 3, 5, 7.

DSA Java

int[] primes = [1] [2];

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

Anew int[]

Bint[]

C{2, 3, 5, 7}

D(2, 3, 5, 7)

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of curly braces for values.

Omitting the new keyword.

Use new int[] followed by curly braces with values to initialize the array.

5fill in blank

hard

Fill all three blanks to declare an array of booleans named flags with size 3 and initialize all values to false.

DSA Java

boolean[] flags = new boolean[[1]];
for(int [2] = 0; [2] < flags.length; [2]++) {
    flags[[3]] = false;
}

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

A3

Bi

Dj

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names in the loop declaration and inside the loop.

Forgetting to initialize all elements.

The array size is 3. The loop variable is i, used to set each element to false.

Practice

1. Which of the following is the correct way to declare and initialize an integer array of size 5 in Java?

easy

A. int[] arr = new int[5];

B. int arr = new int[5];

C. int arr[] = int[5];

D. int[] arr = int[5];

Solution

1. Step 1: Understand Java array declaration syntax

   In Java, arrays are declared with the type followed by square brackets and initialized with the new keyword and size inside square brackets.

2. Step 2: Check each option for correct syntax

   int[] arr = new int[5]; uses correct syntax: int[] arr = new int[5]; Options A, B, and D have syntax errors or missing keywords.

3. Final Answer:

   int[] arr = new int[5]; -> Option A

4. Quick Check:

   Correct Java array declaration = int[] arr = new int[5]; [OK]

Hint: Use 'new' keyword and specify size in brackets [OK]

Common Mistakes:

• Forgetting 'new' keyword
• Using wrong brackets or missing type
• Declaring array without brackets

2. Which of the following is a valid way to declare and initialize an array with values in Java?

easy

A. int[] arr = new int[] {1, 2, 3, 4};

B. int arr[] = new int{1, 2, 3, 4};

C. int[] arr = new int{1, 2, 3, 4};

D. int arr = {1, 2, 3, 4};

Solution

1. Step 1: Understand array initialization with values

   In Java, to initialize an array with values using 'new', syntax is: int[] arr = new int[] {values};

2. Step 2: Check each option

   int[] arr = new int[] {1, 2, 3, 4};: correct syntax. int arr[] = new int{1, 2, 3, 4};: incorrect declaration style and missing [] after new int. int[] arr = new int{1, 2, 3, 4};: missing [] after new int. int arr = {1, 2, 3, 4};: arr not declared as array.

3. Final Answer:

   int[] arr = new int[] {1, 2, 3, 4}; -> Option A

4. Quick Check:

   Array init with 'new int[]' = int[] arr = new int[] {1, 2, 3, 4}; [OK]

Hint: Use 'new int[]' when initializing separately [OK]

Common Mistakes:

• Omitting 'new' when required
• Using wrong brackets
• Assigning values without array type

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

int[] arr = new int[3];
arr[0] = 5;
arr[2] = 10;
System.out.println(arr[1]);

medium

A. 5

B. 0

C. 10

D. Compilation error

Solution

1. Step 1: Understand default values in integer arrays

   When an integer array is created with 'new int[3]', all elements are initialized to 0 by default.

2. Step 2: Check assigned values and output

   arr[0] = 5 and arr[2] = 10 are assigned. arr[1] is not assigned, so it remains 0. The print statement outputs arr[1], which is 0.

3. Final Answer:

   0 -> Option B

4. Quick Check:

   Unassigned int array element = 0 [OK]

Hint: Unassigned int array elements default to 0 [OK]

Common Mistakes:

• Assuming unassigned elements have garbage values
• Confusing index positions
• Expecting runtime error for unassigned index

4. Identify the error in the following Java array declaration:

int arr[5];

medium

A. Missing semicolon at the end

B. Array must be declared with curly braces

C. Array size cannot be specified in declaration without initialization

D. Array size must be a variable, not a number

Solution

1. Step 1: Understand Java array declaration rules

   In Java, you cannot specify the size of the array in the declaration alone. Size must be specified during initialization with 'new'.

2. Step 2: Analyze the given code

   int arr[5]; tries to declare an array with size 5 without initialization, which is invalid syntax in Java.

3. Final Answer:

   Array size cannot be specified in declaration without initialization -> Option C

4. Quick Check:

   Size only with 'new' keyword [OK]

Hint: Specify size only with 'new' keyword during initialization [OK]

Common Mistakes:

• Using C-style array declaration
• Trying to declare size without 'new'
• Confusing declaration and initialization

5. Given the following code, what will be the output?

int[] arr = {1, 2, 3};
arr = new int[] {4, 5};
System.out.print(arr.length);

Choose the correct output and explain why.

hard

A. 3

B. Runtime error

C. Compilation error

D. 2

Solution

1. Step 1: Understand array reassignment

   Initially, arr points to an array of length 3 with values {1, 2, 3}. Then arr is reassigned to a new array with values {4, 5} of length 2.

2. Step 2: Check the length property after reassignment

   After reassignment, arr.length reflects the new array length, which is 2.

3. Final Answer:

   2 -> Option D

4. Quick Check:

   Array length after reassignment = 2 [OK]

Hint: Array variable can point to new array; length updates accordingly [OK]

Common Mistakes:

• Assuming original array length remains
• Expecting error on reassignment
• Confusing array contents with length