Java Arrays: Key Concepts, Declarations, and Examples

Posted on Feb 9, 2025 in Computers

Java Array Fundamentals

Array Size

Once an array is created, its size is fixed.

Declaring Integer Arrays

Which of the following are correct ways to declare an array of int values?

  • int[] a;
  • int a[];

Incorrect Array Declarations

Which of the following are incorrect?

  • int[] a = new int(2);
  • int a = new int[2];
  • int a() = new int[2];

Array Indexing

If you declare an array double[] list = new double[5], the highest index in array list is 4.

Array Length

How many elements are in array double[] list = new double[5]? – 5

Analyzing Code Snippets

Random Number Generation

Analyze the following code:

(int)(Math.random() * 100)

Array Element Access

If you declare an array double[] list = {3.4, 2.0, 3.5, 5.5}, list[1] is 2.0.

Valid Array Statements

Which of the following statements are valid?

  • double d[] = new double[30];
  • int[] i = {3, 4, 3, 2};

Initializing Character Arrays

How can you initialize an array of two characters to ‘a’ and ‘b’?

  • char[] charArray = {'a', 'b'};
  • char[] charArray = new char[2]; charArray[0] = 'a'; charArray[1] = 'b';

Code Analysis with Double Array


double[] myList = {1, 5, 5, 5, 5, 1};
double max = myList[0];
int indexOfMax = 0;
for (int i = 1; i < myList.length; i++) {
 if (myList[i] > max) {
 max = myList[i];
 indexOfMax = i;
 }
}
System.out.println(indexOfMax);

Output: 1

Runtime Error Example

Analyze the following code:


public class Test {
 public static void main(String[] args) {
 int[] x = new int[5];
 int i;
 for (i = 0; i < x.length; i++)
 x[i] = i;
 System.out.println(x[i]);
 }
}

The program has a runtime error because the last statement in the main method causes ArrayIndexOutOfBoundsException.

Output Prediction

What is the output of the following code?


public class Test {
 public static void main(String[] args) {
 double[] x = {2.5, 3, 4};
 for (double value: x)
 System.out.print(value + " ");
 }
}

The program displays 2.5 3.0 4.0.

Array Manipulation

What is the output of the following code?


public class Test {
 public static void main(String[] args) {
 int list[] = {1, 2, 3, 4, 5, 6};
 for (int i = 1; i < list.length; i++)
 list[i] = list[i - 1];
 for (int i = 0; i < list.length; i++)
 System.out.print(list[i] + " ");
 }
}

Output: 1 1 1 1 1 1

Array Assignment

In the following code, what is the output for list2?


public class Test {
 public static void main(String[] args) {
 int[] list1 = {1, 2, 3};
 int[] list2 = {1, 2, 3};
 list2 = list1;
 list1[0] = 0; list1[1] = 1; list2[2] = 2;
 for (int i = 0; i < list2.length; i++)
 System.out.print(list2[i] + " ");
 }
}

Output: 0 1 2

Final Arrays

Analyze the following code:


public class Test {
 public static void main(String[] args) {
 final int[] x = {1, 2, 3, 4};
 int[] y = x;
 x = new int[2];
 for (int i = 0; i < y.length; i++)
 System.out.print(y[i] + " ");
 }
}

The program has a compile error on the statement x = new int[2], because x is final and cannot be changed. The program displays 1 2 3 4.