Array declaration and initialization in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an integer array named numbers.

Java

int[] [1];

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

Aarray

Bnumbers

Clist

Dvalues

Attempts:

3 left

💡 Hint

Common Mistakes

Using invalid variable names like 'list' or 'array' which are not descriptive enough.

Forgetting the semicolon at the end.

The correct way to declare an integer array named numbers is int[] numbers;.

2fill in blank

medium

Complete the code to initialize the array with 5 elements.

Java

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

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

A3

B0

C10

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using zero or negative numbers for the array size.

Confusing the size with the index.

To create an array with 5 elements, use new int[5].

3fill in blank

hard

Fix the error in the array initialization syntax.

Java

int[] numbers = [1] {1, 2, 3, 4, 5};

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

Anew int[]

Bint[]

Cnew int

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the new keyword.

Using int[] without new in this context.

The correct syntax to initialize an array with values is new int[] {1, 2, 3, 4, 5};.

4fill in blank

hard

Fill both blanks to declare and initialize an array with values 10, 20, 30.

Java

int[] [1] = [2] {10, 20, 30};

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

Ascores

Bnew int[]

Cvalues

Dint[]

Attempts:

3 left

💡 Hint

Common Mistakes

Using int[] without new for initialization.

Choosing invalid variable names.

The array name is scores and the initialization requires new int[] before the values.

5fill in blank

hard

Fill all three blanks to create an array of strings with names and print the first element.

Java

String[] [1] = [2] {"Alice", "Bob", "Charlie"};
System.out.println([3][0]);

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

Anames

Bnew String[]

Dlist

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the array in declaration and print statement.

Omitting new String[] in initialization.

The array is named names, initialized with new String[], and printed by accessing names[0].

Practice

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

easy

A. int[] numbers;

B. array int numbers;

C. int numbers[] = new array;

D. int numbers = new int[];

Solution

1. Step 1: Understand Java array declaration syntax

   In Java, arrays are declared by specifying the type followed by square brackets and the variable name.

2. Step 2: Check each option for correct syntax

   int[] numbers; uses int[] numbers; which is the correct syntax. Other options misuse keywords or syntax.

3. Final Answer:

   int[] numbers; -> Option A

4. Quick Check:

   Correct array declaration = int[] numbers; [OK]

Hint: Remember: type[] name; declares an array in Java [OK]

Common Mistakes:

• Using 'array' keyword which doesn't exist in Java
• Assigning new array without specifying size or values
• Placing brackets incorrectly

2. Which of the following lines correctly initializes an array of 5 integers in Java?

easy

A. int arr[] = new int();

B. int arr = new int[5];

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

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

Solution

1. Step 1: Understand array initialization with size

   To create an array of fixed size, use new type[size] syntax.

2. Step 2: Validate each option

   int[] arr = new int[5]; correctly declares and initializes an integer array of size 5. Others have syntax errors or missing size.

3. Final Answer:

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

4. Quick Check:

   Array initialization with size = new int[5] [OK]

Hint: Use new type[size] to initialize arrays in Java [OK]

Common Mistakes:

• Missing square brackets in declaration
• Not specifying size when using new
• Using parentheses instead of brackets

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

int[] nums = {1, 2, 3, 4};
System.out.println(nums[2]);

medium

A. 1

B. 2

C. 3

D. 4

Solution

1. Step 1: Understand array indexing in Java

   Arrays start at index 0, so nums[0]=1, nums[1]=2, nums[2]=3, nums[3]=4.

2. Step 2: Identify the printed element

   The code prints nums[2], which is the third element, value 3.

3. Final Answer:

   3 -> Option C

4. Quick Check:

   Index 2 value = 3 [OK]

Hint: Remember array index starts at 0 in Java [OK]

Common Mistakes:

• Confusing index 2 with the second element
• Off-by-one errors in indexing
• Misreading array initialization

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

int arr[5];

medium

A. Array size cannot be specified in declaration without initialization

B. Missing semicolon at the end

C. Array must be declared as int arr = new int[5];

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 inside square brackets during declaration without initialization.

2. Step 2: Analyze the given code

   int arr[5]; tries to declare an array with size 5 but does not initialize it, which is invalid syntax.

3. Final Answer:

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

4. Quick Check:

   Size only with new keyword = correct [OK]

Hint: Specify size only when using new keyword [OK]

Common Mistakes:

• Trying to declare size in brackets without new
• Confusing Java with C/C++ array syntax
• Forgetting to initialize array after declaration

5. How can you declare and initialize a String array with the values "apple", "banana", and "cherry" in one line in Java?

hard

A. String[] fruits = new String{"apple", "banana", "cherry"};

B. String[] fruits = new String[]{"apple", "banana", "cherry"};

C. String fruits[] = new String[3]{"apple", "banana", "cherry"};

D. String fruits = {"apple", "banana", "cherry"};

Solution

1. Step 1: Understand array initialization with values

   Java allows two ways to initialize arrays with values: shorthand without new keyword only at declaration, or with new keyword and braces.

2. Step 2: Check each option

   String[] fruits = new String[]{"apple", "banana", "cherry"}; is correct. Other options misuse the new keyword by missing brackets after the type, specifying size with initializer list (invalid syntax), or missing array declaration brackets.

3. Final Answer:

   String[] fruits = new String[]{"apple", "banana", "cherry"}; -> Option B

4. Quick Check:

   Use new Type[]{values} for inline initialization [OK]

Hint: Use new Type[]{values} or shorthand only at declaration [OK]

Common Mistakes:

• Mixing shorthand and new keyword incorrectly
• Missing square brackets in declaration
• Assigning array values without brackets