Java Arrays — Why <= Crashed 2.4 Million Records

package io.thecodeforge.java.arrays;

public class ArrayCreation {
    public static void main(String[] args) {

        // --- WAY 1: Declare the array, then fill in the values yourself ---
        // This creates an integer array with exactly 5 slots.
        // Right now every slot holds 0 (Java fills numeric arrays with 0 by default).
        int[] highScores = new int[5];

        // Now we assign values to each slot using its index (0-based)
        highScores[0] = 9500;   // first slot
        highScores[1] = 8750;
        highScores[2] = 8200;
        highScores[3] = 7600;
        highScores[4] = 5100;   // fifth (last) slot — index 4, NOT 5

        // --- WAY 2: Declare AND initialise in one line ---
        // Use this when you already know all the values up front.
        // Java counts the values and sets the size automatically.
        String[] daysOfWeek = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday"};

        // Reading a value back: use the variable name + [index]
        System.out.println("Top score:      " + highScores[0]);  // prints 9500
        System.out.println("Third day:      " + daysOfWeek[2]);  // prints Wednesday

        // .length gives you the number of slots (NOT a method call — no parentheses!)
        System.out.println("Number of days: " + daysOfWeek.length); // prints 5
    }
}

package io.thecodeforge.java.arrays;

public class ArrayIteration {
    public static void main(String[] args) {

        double[] weeklyTemperatures = {18.5, 21.0, 19.3, 23.7, 22.1, 17.8, 20.4};

        // --- CLASSIC for LOOP ---
        // Use when you need the INDEX (position) of each element.
        // i starts at 0 (first slot), runs while i < length (NOT <=), steps by 1.
        System.out.println("=== Daily Forecast ===");
        for (int i = 0; i < weeklyTemperatures.length; i++) {
            // i is the current index; weeklyTemperatures[i] is the value at that index
            System.out.println("Day " + (i + 1) + ": " + weeklyTemperatures[i] + "°C");
        }

        // --- ENHANCED for-each LOOP ---
        // Use when you just want EVERY VALUE and don't need to track position.
        // Reads as: "for each temperature in weeklyTemperatures"
        double total = 0;
        for (double temperature : weeklyTemperatures) {
            total += temperature;  // add each value to the running total
        }

        // Calculate and display the weekly average
        double average = total / weeklyTemperatures.length;
        System.out.printf("%nWeekly average: %.1f°C%n", average);
    }
}

package io.thecodeforge.java.arrays;

public class CinemaSeatingChart {
    public static void main(String[] args) {

        // A cinema with 3 rows, each containing 4 seats.
        // true = seat is booked, false = seat is available.
        // Outer array = rows (3 rows), inner arrays = seats per row (4 each).
        boolean[][] seatBooked = {
            {true,  true,  false, true },   // Row 0 (front)
            {false, false, false, false},   // Row 1 (middle) — all free
            {true,  false, true,  true }    // Row 2 (back)
        };

        System.out.println("=== Cinema Seat Availability ===");
        System.out.println("(O = Available,  X = Booked)\n");

        // Outer loop walks through each ROW
        for (int row = 0; row < seatBooked.length; row++) {
            System.out.print("Row " + (row + 1) + ":  ");

            // Inner loop walks through each SEAT in the current row
            for (int seat = 0; seat < seatBooked[row].length; seat++) {
                // Ternary operator: if booked print X, otherwise print O
                System.out.print(seatBooked[row][seat] ? " X " : " O ");
            }
            System.out.println(); // move to next line after each row
        }

        // Count total available seats using for-each loops
        int availableSeats = 0;
        for (boolean[] row : seatBooked) {          // each row
            for (boolean seat : row) {              // each seat in that row
                if (!seat) availableSeats++;        // if NOT booked, count it
            }
        }
        System.out.println("\nAvailable seats: " + availableSeats);
    }
}

// io.thecodeforge
public class PassingArrays {
    public static void main(String[] args) {
        int[] scores = {95, 87, 73};
        System.out.println("Before: " + java.util.Arrays.toString(scores));
        modifyArray(scores);
        System.out.println("After: " + java.util.Arrays.toString(scores));
    }

    static void modifyArray(int[] arr) {
        arr[0] = 99; // changes original array!
    }
}

// io.thecodeforge
public class ReturningArrays {
    private int[] internalData = {10, 20, 30};

    public int[] getDataUnsafe() {
        return internalData; // caller can mutate!
    }

    public int[] getDataSafe() {
        return java.util.Arrays.copyOf(internalData, internalData.length);
    }

    public static void main(String[] args) {
        ReturningArrays obj = new ReturningArrays();
        int[] bad = obj.getDataUnsafe();
        bad[0] = 999;
        System.out.println(obj.internalData[0]); // prints 999 — bug!
    }
}

// io.thecodeforge
import java.util.Arrays;

public class ArraysUtility {
    public static void main(String[] args) {
        int[] numbers = {5, 3, 8, 1, 2};

        // Print
        System.out.println("Original: " + Arrays.toString(numbers));

        // Sort
        Arrays.sort(numbers);
        System.out.println("Sorted: " + Arrays.toString(numbers));

        // Search (binarySearch requires sorted array)
        int index = Arrays.binarySearch(numbers, 3);
        System.out.println("Index of 3: " + index);

        // Fill
        Arrays.fill(numbers, 0);
        System.out.println("Filled: " + Arrays.toString(numbers));

        // Compare
        int[] other = {0, 0, 0, 0, 0};
        System.out.println("Equals: " + Arrays.equals(numbers, other));
    }
}