Java Arrays Cheat Sheet

int[] intArray;       // Declares an array of integers

String[] strArray;    // Declares an array of strings

intArray = new int[5];  // Creates an array of 5 integers with default values (0)

strArray = new String[5]; // Creates an array of 5 strings with default values (null)

int[] intArray = new int[5];

String[] strArray = new String[5];

int[] intArray = {1, 2, 3, 4, 5};  // Array with values 1, 2, 3, 4, 5

String[] strArray = {"One", "Two", "Three"}; // Array with values "One", "Two", "Three"

int firstElement = intArray[0];  // Access the first element

String secondElement = strArray[1]; // Access the second element

intArray[0] = 10;  // Sets the first element to 10

strArray[1] = "Two Updated"; // Sets the second element to "Two Updated"

String[] fruits = {"Apple", "Orange", "Grapes", "Mango"};

int length = fruits.length;  // Gets the length of the array

for (int i = 0; i < length; i++)
{
	System.out.println(fruits[i]);
}

String[] fruits = {"Apple", "Orange", "Grapes", "Mango"};

for (String fruit : fruits)
{
	System.out.println(fruit);
}

int[][] arr1 = new int[2][2]; // 2 row and 2 column

arr1[0][0] = 1;
arr1[0][1] = 2;
arr1[1][0] = 3;
arr1[1][1] = 4;

for (int i = 0; i < arr1.length; i++)
{
	for (int j = 0; j < arr1[i].length; j++)
	{
		System.out.print(arr1[i][j] + " "); // 1 2 3 4
	}
}

System.out.println();

int[][] arr2 = {{1, 2, 3}, {2, 4, 5}, {4, 4, 5}};

for (int i = 0; i < 3; i++)
{
	for (int j = 0; j < 3; j++)
	{
		System.out.print(arr2[i][j] + " "); // 1 2 3 2 4 5 4 4 5
	}
}

int[][] jaggedArray = new int[3][];

jaggedArray[0] = new int[5];

jaggedArray[1] = new int[3];

jaggedArray[2] = new int[4];

public static void modifyArray(int[] array) {
    array[0] = 100;  // Modifies the first element of the array
}

public static int[] createArray() {
    return new int[]{1, 2, 3, 4, 5};
}

// Copying Arrays

// Following code copies entire array
int[] newArray = Arrays.copyOf(intArray, intArray.length); 

// Following code copies elements from index 1 to 3
int[] partialArray = Arrays.copyOfRange(intArray, 1, 4); 

// Filling Arrays

// Following code fills the entire array with 10
Arrays.fill(intArray, 10); 

// Sorting Arrays

// Following code sorts the array in ascending order
Arrays.sort(intArray);

// Searching Arrays

// Following code searches for element 3, returns its index
int index = Arrays.binarySearch(intArray, 3);

// Comparing Arrays

// Following code compares two arrays for equality
boolean isEqual = Arrays.equals(intArray, newArray); 

// Converting Array to String

// Following code converts array to a string representation
String arrayString = Arrays.toString(intArray);

// Cloning Arrays

// Following code creates a shallow copy of the array
int[] clonedArray = intArray.clone();

// Array to List Conversion

// Following code converts array to a fixed-size list
List<String> strList = Arrays.asList(strArray);

// List to Array Conversion

// Following code converts list back to array
String[] newArray = strList.toArray(new String[0]);

class Student {
    String name;
    int age;
    
    Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

// Array of 3 Student objects
Student[] students = new Student[3];

// Assigning Student objects to the array
students[0] = new Student("Alice", 20);

students[1] = new Student("Bob", 22);

students[2] = new Student("Charlie", 19);

// Accessing the name of the first student
String studentName = students[0].name;

// Modifying the age of the second student
students[1].age = 23;

for (Student student : students) {
    System.out.println(student.name + " is " + student.age + " years old.");
}

// Convert Array to Stream

// Following code creates a stream from an int array
IntStream intStream = Arrays.stream(intArray);

// Following code creates a stream from a String array
Stream<String> strStream = Arrays.stream(strArray);

// Filtering an Array Using Streams

// Following code filters even numbers
int[] evenNumbers = Arrays.stream(intArray).filter(x -> x % 2 == 0).toArray(); 

// Mapping and Collecting Stream Results

// Following code squares each element
int[] squaredNumbers = Arrays.stream(intArray).map(x -> x * x).toArray();

// Reducing an Array to a Single Value

Following code sums all elements in the array
int sum = Arrays.stream(intArray).reduce(0, (a, b) -> a + b);

public static void printNumbers(int... numbers) {
    for (int number : numbers) {
        System.out.println(number);
    }
}

// Calls method with multiple arguments
printNumbers(1, 2, 3, 4, 5);

public static void printNumbers(int[] numbers) {
    for (int number : numbers) {
        System.out.println(number);
    }
}

// Calls method with array as argument
printNumbers(new int[]{1, 2, 3, 4, 5});