Array Programs in Java | Beginner to Expert Level

5 mins read76 Views Comment

Associate Senior Executive

Updated on Nov 23, 2023 12:05 IST

Array programs in Java traverse from basic single-dimensional arrays to complex multi-dimensional arrays and dynamic arrays using ArrayList. From initializing and accessing array elements to advanced operations like sorting and searching, arrays facilitate efficient data management and manipulation, forming a fundamental concept for every aspiring Java developer.

An Array Program typically refers to a program that utilizes array data structures that can hold more than one value at a time. Arrays are used in programming to organize a series of items sequentially.

Read more: Arrays in Java.

This blog will help you learn Array Programs in Java from Beginner (Level 1) to Expert (Level 4).

Level 1 (Beginners)

Here, we will see some very basic array programs!

Question 1: Creating and Initializing an Array

public class Main {
    public static void main(String[] args) {
        int[] myArray = {1, 2, 3, 4, 5};
        System.out.println("Array created with elements: " + java.util.Arrays.toString(myArray));
    }
}
Copy code

Output

Array created with elements: [1, 2, 3, 4, 5]

Question 2: Accessing Elements of an Array

public class Main {
    public static void main(String[] args) {
        int[] myArray = {1, 2, 3, 4, 5};
        System.out.println("The first element is: " + myArray[1]);
        System.out.println("The fourth element is: " + myArray[4]);
    }
}
Copy code

Output

The first element is: 2
The fourth element is: 5

Question 3: Modifying Elements of an Array

public class Main {
    public static void main(String[] args) {
        int[] myArray = {1, 2, 3, 4, 5};
        myArray[1] = 10;
        System.out.println("Array after modification: " + java.util.Arrays.toString(myArray));
    }
}
Copy code

Output

Array after modification: [1, 10, 3, 4, 5]

Question 4: Finding the Length of an Array

public class Main {
    public static void main(String[] args) {
        int[] myArray = {1, 2, 3, 4, 6};
        System.out.println("The length of the array is: " + myArray.length);
    }
}
Copy code

Output

The length of the array is: 5

Question 5: Looping through an Array

public class Main {
    public static void main(String[] args) {
        int[] myArray = {1, 2, 3, 4, 5};
        for(int i = 0; i < myArray.length; i++) {
            System.out.println("Element at index " + i + ": " + myArray[i]);
        }
    }
}
Copy code

Output

Element at index 0: 1
Element at index 1: 2
Element at index 2: 3
Element at index 3: 4
Element at index 4: 5

Question 6: Multi-dimensional Arrays

public class Main {
    public static void main(String[] args) {
        int[][] multiArray = { {1, 2}, {3, 4}, {5, 6} };
        System.out.println("Element at row 1 column 1: " + multiArray[0][0]);
    }
}
Copy code

Output

Element at row 1 column 1: 1

Question 7: Copying Arrays

public class Main {
    public static void main(String[] args) {
        int[] myArray = {1, 2, 3, 4, 5};
        int[] newArray = java.util.Arrays.copyOf(myArray, myArray.length);
        System.out.println("Copied array: " + java.util.Arrays.toString(newArray));
    }
}
Copy code

Output

Copied array: [1, 2, 3, 4, 5]

Question 8: Sorting Arrays

public class Main {
    public static void main(String[] args) {
        int[] myArray = {5, 3, 4, 1, 2};
        java.util.Arrays.sort(myArray);
        System.out.println("Sorted array: " + java.util.Arrays.toString(myArray));
    }
}
Copy code

Output

Sorted array: [1, 2, 3, 4, 5]

Level 2 (Intermediate Level)

Question 1: Find the Second Largest Number in an Array

public class Main {
    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5, 6};
        int largest = Integer.MIN_VALUE;
        int secondLargest = Integer.MIN_VALUE;

        for(int num : arr) {
            if(num > largest) {
                secondLargest = largest;
                largest = num;
            } else if(num > secondLargest && num != largest) {
                secondLargest = num;
            }
        }

        System.out.println("The second largest number is: " + secondLargest);
    }
}
Copy code

Output

The second largest number is: 5

Question 2: Reverse an Array

public class Main {
    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5};
        int n = arr.length;

        for(int i = 0; i < n / 2; i++) {
            int temp = arr[i];
            arr[i] = arr[n - i - 1];
            arr[n - i - 1] = temp;
        }

        System.out.println("Reversed array: " + java.util.Arrays.toString(arr));
    }
}
Copy code

Output

Reversed array: [5, 4, 3, 2, 1]

Question 3: Find the Duplicate Elements

import java.util.HashSet;
import java.util.Set;

public class Main {
    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 2, 5, 6, 3};
        Set<Integer> set = new HashSet<>();
        Set<Integer> duplicates = new HashSet<>();

        for(int num : arr) {
            if(!set.add(num)) {
                duplicates.add(num);
            }
        }

        System.out.println("Duplicate elements: " + duplicates);
    }
}
Copy code

Output

Duplicate elements: [2, 3]

Question 4: Find the Kth Largest and Smallest Element in an Array

public class Main {
    public static void main(String[] args) {
        int[] arr = {7, 5, 9, 3, 2, 8, 1, 6};
        int k = 5;
        java.util.Arrays.sort(arr);
        System.out.println(k + "th largest element: " + arr[arr.length - k]);
        System.out.println(k + "th smallest element: " + arr[k - 1]);
    }
}
Copy code

Output

5th largest element: 5
5th smallest element: 6

Question 5: Move all Zeroes to the End of the Array

public class Main {
    public static void main(String[] args) {
        int[] arr = {1, 0, 2, 0, 3, 0, 4, 0};
        int n = arr.length;
        int count = 0;

        for(int i = 0; i < n; i++) {
            if(arr[i] != 0) {
                arr[count++] = arr[i];
            }
        }
        while(count < n) {
            arr[count++] = 0;
        }

        System.out.println("Array after moving zeroes: " + java.util.Arrays.toString(arr));
    }
}
Copy code

Output

Array after moving zeroes: [1, 2, 3, 4, 0, 0, 0, 0]

Question 6: Find the “Leaders” in an Array

public class Main {
    public static void main(String[] args) {
        int[] arr = {16, 17, 4, 3, 5, 2};
        int n = arr.length;
        int maxFromRight = arr[n - 1];

        System.out.print("Leaders: " + maxFromRight + " ");

        for(int i = n - 2; i >= 0; i--) {
            if(arr[i] > maxFromRight) {
                maxFromRight = arr[i];
                System.out.print(maxFromRight + " ");
            }
        }
    }
}
Copy code

Output

Leaders: 2 5 17

A leader in an array is an element which is larger than all the elements to its right side, which is what you can see in the above output.

Question 7: Find the Majority Element

Understanding ArrayList in Java

The below article goes through explaining ArrayList in Java with suitable examples. It covers the creation and operations on ArrayList along with a few methods in it. Let’s begin!

Implementing Array in Java

Arrays in Java help to maintain elements of same datatype under a single variable name. The below article explains the implementation of array in java with examples.

Understanding Data Structures and Algorithms in Java

Data Structure in Java is used to store and organize data efficiently while the algorithms are used to manipulate the data in that structure. In this article, we will briefly...read more

public class Main {
    public static void main(String[] args) {
        int[] arr = {3, 3, 4, 2, 4, 4, 2, 4, 4};
        int candidate = findCandidate(arr);
        if(isMajority(arr, candidate)) {
            System.out.println("Majority element is: " + candidate);
        } else {
            System.out.println("No majority element found");
        }
    }

    static int findCandidate(int[] arr) {
        int majIndex = 0, count = 1;
        for(int i = 1; i < arr.length; i++) {
            if(arr[majIndex] == arr[i]) {
                count++;
            } else {
                count--;
            }
            if(count == 0) {
                majIndex = i;
                count = 1;
            }
        }
        return arr[majIndex];
    }

    static boolean isMajority(int[] arr, int candidate) {
        int count = 0;
        for(int num : arr) {
            if(num == candidate) {
                count++;
            }
        }
        return count > arr.length / 2;
    }
}
Copy code

Output

Majority element is: 4

A majority element in an array is an element that appears more than n/2 times where n is the size of the array, which is what you can see in the above output.

Question 8: Rotate Array by N Elements

public class Main {
    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5, 6, 7};
        int n = 2; // Number of positions to rotate
        reverseArray(arr, 0, n - 1);
        reverseArray(arr, n, arr.length - 1);
        reverseArray(arr, 0, arr.length - 1);

        System.out.println("Rotated array: " + java.util.Arrays.toString(arr));
    }

    static void reverseArray(int[] arr, int start, int end) {
        while(start < end) {
            int temp = arr[start];
            arr[start] = arr[end];
            arr[end] = temp;
            start++;
            end--;
        }
    }
}
Copy code

Output

Rotated array: [3, 4, 5, 6, 7, 1, 2]

Level 3 (Advanced Level)

Question 1: Maximum Subarray Sum (Kadane’s Algorithm)

public class Main {
    public static void main(String[] args) {
        int[] nums = {-2,1,-3,4,-1,2,1,-5,4};
        System.out.println(maxSubArray(nums));
    }

    public static int maxSubArray(int[] nums) {
        int maxSoFar = nums[0], maxEndingHere = nums[0];
        for(int i = 1; i < nums.length; i++) {
            maxEndingHere = Math.max(maxEndingHere + nums[i], nums[i]);
            maxSoFar = Math.max(maxSoFar, maxEndingHere);
        }
        return maxSoFar;
    }
}
Copy code

Output

Question 2: Longest Increasing Subsequence

public class Main {
    public static void main(String[] args) {
        int[] nums = {10, 22, 9, 33, 21, 50, 41, 60};
        System.out.println(lengthOfLIS(nums));
    }

    public static int lengthOfLIS(int[] nums) {
        int[] dp = new int[nums.length];
        int length = 0;

        for(int num : nums) {
            int i = java.util.Arrays.binarySearch(dp, 0, length, num);
            if(i < 0) i = -(i + 1);
            dp[i] = num;
            if(i == length) length++;
        }
        return length;
    }
}
Copy code

Output

Question 3: Matrix Spiral Traversal

public class Main {
    public static void main(String[] args) {
        int[][] matrix = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
        System.out.println(spiralOrder(matrix));
    }

    public static java.util.List<Integer> spiralOrder(int[][] matrix) {
        java.util.List<Integer> res = new java.util.ArrayList<>();
        if(matrix.length == 0) return res;
        int rowBegin = 0, rowEnd = matrix.length - 1;
        int colBegin = 0, colEnd = matrix[0].length - 1;

        while(rowBegin <= rowEnd && colBegin <= colEnd) {
            for(int j = colBegin; j <= colEnd; j++) {
                res.add(matrix[rowBegin][j]);
            }
            rowBegin++;
            for(int j = rowBegin; j <= rowEnd; j++) {
                res.add(matrix[j][colEnd]);
            }
            colEnd--;
            if(rowBegin <= rowEnd) {
                for(int j = colEnd; j >= colBegin; j--) {
                    res.add(matrix[rowEnd][j]);
                }
            }
            rowEnd--;
            if(colBegin <= colEnd) {
                for(int j = rowEnd; j >= rowBegin; j--) {
                    res.add(matrix[j][colBegin]);
                }
            }
            colBegin++;
        }
        return res;
    }
}
Copy code

Output

[1, 2, 3, 6, 9, 8, 7, 4, 5]

Question 4: Median of Two Sorted Arrays

public class Main {
    public static void main(String[] args) {
        int[] nums1 = {1, 3};
        int[] nums2 = {2};
        System.out.println(findMedianSortedArrays(nums1, nums2));
    }

    public static double findMedianSortedArrays(int[] nums1, int[] nums2) {
        if(nums1.length > nums2.length) {
            int[] temp = nums1; nums1 = nums2; nums2 = temp;
        }
        int m = nums1.length, n = nums2.length;
        int imin = 0, imax = m, halfLen = (m + n + 1) / 2;
        double median = 0.0;

        while(imin <= imax) {
            int i = (imin + imax) / 2;
            int j = halfLen - i;

            if(i < m && nums2[j-1] > nums1[i]) {
                imin = i + 1;
            } else if(i > 0 && nums1[i-1] > nums2[j]) {
                imax = i - 1;
            } else {
                int maxOfLeft = 0;
                if(i == 0) maxOfLeft = nums2[j-1];
                else if(j == 0) maxOfLeft = nums1[i-1];
                else maxOfLeft = Math.max(nums1[i-1], nums2[j-1]);

                if((m + n) % 2 == 1) return maxOfLeft;

                int minOfRight = 0;
                if(i == m) minOfRight = nums2[j];
                else if(j == n) minOfRight = nums1[i];
                else minOfRight = Math.min(nums1[i], nums2[j]);

                return (maxOfLeft + minOfRight) / 2.0;
            }
        }
        return median;
    }
}
Copy code

Output

2.0

Question 5: Maximum Product Subarray

public class Main {
    public static void main(String[] args) {
        int[] nums = {2,3,-2,4};
        System.out.println(maxProduct(nums));
    }

    public static int maxProduct(int[] nums) {
        if(nums.length == 0) return 0;
        int maxSoFar = nums[0], minSoFar = nums[0], result = nums[0];
        for(int i = 1; i < nums.length; i++) {
            if(nums[i] < 0) {
                int temp = maxSoFar;
                maxSoFar = minSoFar;
                minSoFar = temp;
            }
            maxSoFar = Math.max(nums[i], maxSoFar * nums[i]);
            minSoFar = Math.min(nums[i], minSoFar * nums[i]);
            result = Math.max(result, maxSoFar);
        }
        return result;
    }
}
Copy code

Output

Level 4 (Expert)

Problem Statement: Question 1

Given a list of buildings where each building is represented by triplets [Li,Ri,Hi] :

Li: An integer, representing the left position of the building.
Ri: An integer, representing the right position of the building.
Hi: An integer, representing the height of the building.

Calculate the skyline formed by these buildings.

Input Format:

A list of n building triplets. Each triplet contains three integers.
1≤n≤10⁵
0≤Li,Ri,Hi≤10⁴

Output Format:

A list of key-height pairs representing the skyline.

Solution:

import java.util.*;
import java.util.stream.*;

public class Main {

    public static void main(String[] args) {
        int[][] buildings = {{2, 9, 10}, {3, 7, 15}, {5, 12, 12}, {15, 20, 10}, {19, 24, 8}};
        List<List<Integer>> result = getSkyline(buildings);
        for (List<Integer> point : result) {
            System.out.println(point);
        }
    }

    public static List<List<Integer>> getSkyline(int[][] buildings) {
        List<int[]> heights = new ArrayList<>();
        for (int[] b : buildings) {
            heights.add(new int[]{b[0], -b[2]});
            heights.add(new int[]{b[1], b[2]});
        }

        Collections.sort(heights, (a, b) -> {
            if (a[0] != b[0]) return a[0] - b[0];
            return a[1] - b[1];
        });

        PriorityQueue<Integer> pq = new PriorityQueue<>((a, b) -> (b - a));
        pq.offer(0);
        int prev = 0;
        List<List<Integer>> result = new ArrayList<>();

        for (int[] h : heights) {
            if (h[1] < 0) {
                pq.offer(-h[1]);
            } else {
                pq.remove(h[1]);
            }
            int cur = pq.peek();
            if (prev != cur) {
                result.add(Arrays.asList(h[0], cur));
                prev = cur;
            }
        }

        return result;
    }
}
Copy code

Output

[2, 10]
[3, 15]
[7, 12]
[12, 0]
[15, 10]
[20, 8]
[24, 0]

Problem Statement: Question 2

Given a 2D matrix of dimensions m x n containing integers, find the rectangle (sub-matrix) with the maximum sum of its elements.

Input Format:

A 2D matrix of size m x n where 1≤m,n≤100
Matrix values: −10⁴≤matrix[i][j]≤10⁴

Output Format:

An integer representing the maximum sum.

Solution:

import java.util.Arrays;
import java.util.TreeSet;

public class Main {
    public static void main(String[] args) {
        int[][] matrix = {
            {1, 2, -1, -4, -20},
            {-8, -3, 4, 2, 1},
            {3, 8, 10, 1, 3},
            {-4, -1, 1, 7, -6}
        };
        System.out.println("Maximum Sum of Sub-matrix: " + maxSumRectangle(matrix));
    }

    public static int maxSumRectangle(int[][] M) {
        int m = M.length, n = M[0].length;
        int[] sums = new int[m];
        int maxSum = Integer.MIN_VALUE;

        for (int left = 0; left < n; left++) {
            Arrays.fill(sums, 0);

            for (int right = left; right < n; right++) {
                for (int i = 0; i < m; i++) {
                    sums[i] += M[i][right];
                }
                
                TreeSet<Integer> set = new TreeSet<>();
                set.add(0);
                int curSum = 0;

                for (int sum : sums) {
                    curSum += sum;
                    Integer num = set.ceiling(curSum - maxSum);
                    if (num != null) {
                        maxSum = Math.max(maxSum, curSum - num);
                    }
                    set.add(curSum);
                }
            }
        }
        return maxSum;
    }
}
Copy code

Output

Maximum Sum of Sub-matrix: 1

Nested If Else in Java | About, Syntax, Flowchart and Examples

Have you ever wondered how programs make decisions and adapt to different situations? The answer lies in the power of Nested If else statements. These statements allow us to control...read more

Java Comments | About, Types and Examples

Do you know what makes the code more readable? Comments, as they provide valuable context and explanations about the code, making it easier for both the original developers and others...read more

Star Pattern Programs in Java

Pattern programs in Java are a type of problem that use nested loops to produce different patterns of numbers, stars (*), or other characters. In this blog we will dive...read more

Number Pattern Programs in Java

Pattern programs in Java are a type of problem that use nested loops to produce different patterns of numbers, stars (*), or other characters. In this blog we will dive...read more

A Guide to Power Function in Java

Have you ever wondered how mathematical power functions are implemented in programming languages like Java? In Java, the Math.pow() function is a powerful tool used to raise a number to...read more

Conclusion

Thus, I hope all the questions help you understand the concept better. Keep learning, Keep exploring!

Download this article as PDF to read offline

Download as PDF

About the Author

Esha Gupta

Associate Senior Executive

I'm Esha Gupta, a B.Tech graduate in Computer Science & Engineering, specializing in Front End Web Dev. I've interned at GeeksforGeeks & Coding Minutes, fueling my passion for crafting appealing and functional digit... Read Full Bio

Array Programs in Java | Beginner to Expert Level

Table of Content

Level 1 (Beginners)

Question 1: Creating and Initializing an Array

Question 2: Accessing Elements of an Array

Question 3: Modifying Elements of an Array

Question 4: Finding the Length of an Array

Question 5: Looping through an Array

Question 6: Multi-dimensional Arrays

Question 7: Copying Arrays

Question 8: Sorting Arrays

Level 2 (Intermediate Level)

Question 1: Find the Second Largest Number in an Array

Question 2: Reverse an Array

Question 3: Find the Duplicate Elements

Question 4: Find the Kth Largest and Smallest Element in an Array

Question 5: Move all Zeroes to the End of the Array

Question 6: Find the “Leaders” in an Array

Question 7: Find the Majority Element

Question 8: Rotate Array by N Elements

Level 3 (Advanced Level)

Question 1: Maximum Subarray Sum (Kadane’s Algorithm)

Question 2: Longest Increasing Subsequence

Question 3: Matrix Spiral Traversal

Question 4: Median of Two Sorted Arrays

Question 5: Maximum Product Subarray

Level 4 (Expert)

Problem Statement: Question 1

Problem Statement: Question 2

Conclusion

Comments

Trending Technology Courses

Top Picks & New Arrivals