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How do you declare and initialize an array of objects (reference types) versus an array of primitives, and what is the key difference in their default values? How do multidimensional arrays work in Java, and how do they differ from truly rectangular arrays in languages like C? What utility methods does java.util.Arrays provide for common array operations like sorting, searching, filling, and comparing? How do you convert between an array and a List (ArrayList) in both directions, and what pitfalls exist with Arrays.asList()? How does Java handle array bounds checking, and what exception is thrown when accessing an invalid index? How do you correctly iterate a 2D array using both traditional indexed for-loops and the enhanced for-each loop, and when is each approach preferable? What is array covariance's relationship to generic arrays, and why can't you directly create a generic array like new T[10] or new List<String>[10]? How would you flatten a 2D array into a 1D array, and conversely, reshape a 1D array into a 2D array? How does Java implement covariant array typing, and why is this considered a design flaw that can lead to runtime ArrayStoreException? How would you efficiently copy, resize, or merge large arrays in Java, and what are the performance trade-offs between System.arraycopy(), Arrays.copyOf(), and manual loops?
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How do you declare, initialize, and access elements of a one-dimensional array in Java?

Beginner

Answer

An array is declared with a type followed by square brackets (int[] arr), instantiated with new specifying its fixed size (new int[5]) or using an initializer literal ({1, 2, 3}), and accessed/modified via zero-based indexing (arr[0]) -- once created, an array's length is fixed and immutable for its lifetime, unlike a resizable collection like ArrayList.
int[] numbers = new int[5];  // all elements default to 0
numbers[0] = 10;
numbers[1] = 20;

int[] literal = {1, 2, 3, 4, 5};  // initializer syntax
System.out.println(literal[2]);  // prints 3
System.out.println(literal.length);  // prints 5, note: .length is a field, not a method
Real-world example A fixed-size lookup table mapping day-of-week integers (0-6) to day names is implemented as a simple String array, appropriate since the collection's size is known and fixed at compile time and never needs to grow or shrink.

Common follow-ups: Why is array.length a field access rather than a method call, unlike String's .length()?;What happens if you access an index outside the array's bounds?

Collections Framework;Java Fundamentals: Syntax Data Types & Operators
All 15 Arrays & Multidimensional Arrays questions