Arrays in Java Chapter 1

Understanding Arrays

• A collection of elements of the same data type is known as an array.
• Arrays are used to store and manipulate data efficiently.
• An array is initialized with a specific size, which defines the number of elements it can hold.

Creating an Array

• The correct syntax to create an array in Java, with an example, is int a[] = new int[3]:
  • int specifies the data type (integer).
  • a[] declares the array name.
  • new int[3] allocates memory for an array of size 3, the size is specified in square brackets.

Accessing Array Elements

• Array elements are indexed beginning from 0.
• In an array of size 5, the element at index 4 represents the fifth element.

Array Size in Bytes

• The size of an array depends on the data type and number of elements.
• In the example, an array with 5 int elements (each int is 4 bytes) has a total size of 20 bytes (5 * 4).

Arrays in Java

• Arrays in Java store a collection of elements of the same data type.
• Elements are accessed using an index, starting from 0.
• The array's length is fixed at creation.
• Use the length property to get the array size.
• Array indices are used to retrieve individual elements.
• You can create zero-length arrays.

Array Index Out of Bounds Exception

• ArrayIndexOutOfBoundsException happens when accessing an index outside the array's valid range.
• This is a runtime error, arising from indexes less than zero or greater than or equal to the array length.

Passing Arrays to Methods

• Passing an array to a method sends a reference to the array.
• Changes made to the array inside the method modify the original array.
• To create copies, manually copy elements to a new array.

Array Declaration and Initialization

• An array is declared using data_type[] array_name;
• data_type can be a primitive or reference type.
• Initialize with values: data_type[] array_name = {value1, value2, ...};
• Create with allocation: data_type[] array_name = new data_type[size];
• size specifies the number of elements.

Array Manipulation

• Array operations include accessing, modifying elements, finding the length, sorting (Arrays.sort()), searching (Arrays.binarySearch()), and creating copies (Arrays.copyOf()).

Common Array Operations

• Finding the maximum value: Use Math.max().
• Character array operations:
  • Character addition: Converts characters to ASCII values and adds them.
  • Concatenation: Use + to concatenate character arrays with strings or other characters.

Key Concepts

• Compile-time error: An error identified during compilation due to invalid syntax.
• Runtime error: An error detected during program execution, often from unexpected behaviour or incorrect conditions (like accessing an invalid array index).

Best Practices

• Avoid ArrayIndexOutOfBoundsException by ensuring valid indices when accessing array elements.
• Use the length property to obtain the array's size.
• Be mindful of data types and conversions in arithmetic operations, particularly with character arrays, where implicit ASCII conversion might happen.