Array declaration and initialization in Java - Mini Project: Build & Apply

Array declaration and initialization

📖 Scenario: You are helping a small store keep track of the prices of some fruits they sell. You will create an array to store these prices.

🎯 Goal: Create an array to hold fruit prices, set a size, fill it with values, and then print the prices.

📋 What You'll Learn

Declare an array of type double called fruitPrices

Initialize the array with a size of 4

Assign the prices 1.99, 2.49, 0.99, and 3.49 to the array elements

Print all the prices in the array

💡 Why This Matters

🌍 Real World

Arrays are used to store lists of data like prices, names, or measurements in many software applications.

💼 Career

Understanding arrays is essential for programming jobs because they help manage collections of data efficiently.

1

Declare and initialize the array

Declare an array of type double called fruitPrices and initialize it with size 4.

Java

// Your code here

Hint

Use double[] fruitPrices = new double[4]; to create the array.

2

Assign prices to the array elements

Assign the prices 1.99, 2.49, 0.99, and 3.49 to the array elements fruitPrices[0], fruitPrices[1], fruitPrices[2], and fruitPrices[3] respectively.

Java

public class Main {
    public static void main(String[] args) {
        double[] fruitPrices = new double[4];
        // Your code here
    }
}

Hint

Assign each price to the correct index like fruitPrices[0] = 1.99;

3

Use a for loop to print all prices

Use a for loop with variable i from 0 to 3 to print each price in fruitPrices[i] using System.out.println.

Java

public class Main {
    public static void main(String[] args) {
        double[] fruitPrices = new double[4];
        fruitPrices[0] = 1.99;
        fruitPrices[1] = 2.49;
        fruitPrices[2] = 0.99;
        fruitPrices[3] = 3.49;
        // Your code here
    }
}

Hint

Use a for loop from 0 to 3 and print each element with System.out.println(fruitPrices[i]);

4

Print all fruit prices

Run the program to print all the fruit prices stored in the fruitPrices array.

Java

public class Main {
    public static void main(String[] args) {
        double[] fruitPrices = new double[4];
        fruitPrices[0] = 1.99;
        fruitPrices[1] = 2.49;
        fruitPrices[2] = 0.99;
        fruitPrices[3] = 3.49;
        for (int i = 0; i < 4; i++) {
            System.out.println(fruitPrices[i]);
        }
    }
}
// Your code here

Hint

Run the program and check the output matches the prices.

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