Java and Object-Oriented Programming - Basics to Advanced

In Java, arrays are special container objects that hold a fixed number of elements of a single type, allowing efficient storage and random access to data. The array itself is an object derived from the Object class, which means it has properties like length and can be passed to methods or returned from them. Arrays can be one-dimensional (e.g., int[] nums = new int[5];), multidimensional (e.g., int[][] matrix = new int[3][3];), or even jagged (arrays of arrays with varying lengths). Once created, the size of an array cannot change, which makes it suitable for scenarios where the number of elements is known in advance.

Although arrays are built into Java’s syntax, the java.util.Arrays class provides many useful utility methods for manipulating them. This includes methods such as Arrays.sort() for sorting, Arrays.binarySearch() for searching, and Arrays.equals() or Arrays.deepEquals() for comparing arrays. You can also use Arrays.copyOf() and Arrays.fill() to duplicate or initialize array values easily. For displaying contents, Arrays.toString() and Arrays.deepToString() convert arrays to human-readable string forms, which is particularly helpful for debugging.

Java arrays can store either primitive types (like int, char, double) or object references (like String, Integer). When used with objects, only references are stored, not the actual objects themselves. Since arrays are fixed-size, when flexibility is needed—such as dynamic resizing or type-safe operations—collections like ArrayList are typically preferred. However, arrays remain fundamental in Java because of their simplicity, performance efficiency, and direct memory representation, which make them essential for low-level data structures, numerical computations, and performance-critical applications.

Standard Poker Hand Ranking

There are 52 cards in the pack, and the ranking of the individual cards, from high to low, is ace, king, queen, jack, 10, 9, 8, 7, 6, 5, 4, 3, 2. There is no ranking between the suits – so for example the king of hearts and the king of spades are equal.

A poker hand consists of five cards. The categories of hand, from highest to lowest, are listed below. Any hand in a higher category beats any hand in a lower category (so for example any three of a kind beats any two pairs). Between hands in the same category the rank of the individual cards decides which is better, as described in more detail below.

S=Spades C= Clubs H= Hearts D=Diamonds

1. Royal Flush

This is the highest poker hand. It consists of ace, king, queen, jack, ten, all in the same suit. If there are 2 royal flushes in the running for High hand, then the ranking order from highest to lowest is Spades, Hearts, Diamonds and Clubs.

2. Straight Flush

Five cards of the same suit in sequence – such as CJ-C10-C9-C8-C7. Between two straight flushes, the one containing the higher top card is higher. An ace can be counted as low, so H5-H4-H3-H2-HA is a straight flush, but its top card is the five, not the ace, so it is the lowest type of straight flush. The cards cannot “turn the corner”:D4-D3-D2-DA-DK is not valid.

3. Four of a kind

Four cards of the same rank – such as four queens. The fifth card can be anything. This combination is sometimes known as “quads”, and in some parts of Europe it is called a “poker”, though this term for it is unknown in English. Between two fours of a kind, the one with the higher set of four cards is higher – so 3-3-3-3-A is beaten by 4-4-4-4-2. In Texas Hold’em, if the board shows “quads”, then the player with the higher fifth card is the winner.

4. Full House

This consists of three cards of one rank and two cards of another rank – for example three sevens and two tens (colloquially known as “sevens full” or more specifically “sevens on tens”). When comparing full houses, the rank of the three cards determines which is higher. For example 9-9-9-4-4 beats 8-8-8-A-A. If the threes of a kind were equal, the rank of the pairs would decide.

5. Flush

Five cards of the same suit. When comparing two flushes, the highest card determines which is higher. If the highest cards are equal then the second highest card is compared; if those are equal too, then the third highest card, and so on. For example SK-SJ-S9-S3-S2 beats DK-DJ-D7-D6-D5 because the nine beats the seven.

6. Straight

Five cards of mixed suits in sequence – for example SQ-DJ-H10-S9-C8. When comparing two sequences, the one with the higher ranking top card is better. Ace can count high or low in a straight, but not both at once, so A-K-Q-J-10 and 5-4-3-2-A are valid straights, but 2-A-K-Q-J is not. 5-4-3-2-A is the lowest kind of straight, the top card being the five.

7. Three of a Kind

Three cards of the same rank plus two other cards. This combination is also known as Triplets or Trips. When comparing two threes of a kind the hand in which the three equal cards are of higher rank is better. So for example 5-5-5-3-2 beats 4-4-4-K-Q. If you have to compare two threes of a kind where the sets of three are of equal rank, then the higher of the two remaining cards in each hand are compared, and if those are equal, the lower odd card is compared.

8. Two Pair

A pair is two cards of equal rank. In a hand with two pairs, the two pairs are of different ranks (otherwise you would have four of a kind), and there is an odd card to make the hand up to five cards. When comparing hands with two pairs, the hand with the highest pair wins, irrespective of the rank of the other cards – so J-J-2-2-4 beats 10-10-9-9-8 because the jacks beat the tens. If the higher pairs are equal, the lower pairs are compared, so that for example 8-8-6-6-3 beats 8-8-5-5-K. Finally, if both pairs are the same, the odd cards are compared, so Q-Q-5-5-8 beats Q-Q-5-5-4.

9. Pair

A hand with two cards of equal rank and three other cards which do not match these or each other. When comparing two such hands, the hand with the higher pair is better – so for example 6-6-4-3-2 beats 5-5-A-K-Q. If the pairs are equal, compare the highest ranking odd cards from each hand; if these are equal compare the second highest odd card, and if these are equal too compare the lowest odd cards. So J-J-A-9-3 beats J-J-A-8-7 because the 9 beats the 8.

10. High Card

Five cards which do not form any of the combinations listed above. When comparing two such hands, the one with the better highest card wins. If the highest cards are equal the second cards are compared; if they are equal too the third cards are compared, and so on. So A-J-9-5-3 beats A-10-9-6-4 because the jack beats the ten.