Java Polymorphism: Child Class Method Overriding

This question is a good example to understand concepts of constructor and inheritance. For the First question: Child class show() method will be called because child class object is created and it overrides the parent class show() method. For the Second question: The output might be 0 because when child class object is created it will first call parent class constructor which then call the overridden show method and print the value of x i.e. 0(Because JVM will first assign default values to the variables after creating the child class object and calls parent constructor first). For the Third question: This can cause security flaws in the code and can result in Null Pointer Exception. You should never call the overridden methods from the constructor, and if you have to call a method from constructor make the method final first.

Stop incrementing shared counters with ++ like it’s 2005. In Java, the ++ operation follows a read → add → write sequence. When multiple threads access it simultaneously, updates can collide, leading to lost increments. Here are some guidelines for safer incrementing: - Use ++ when the value is thread-confined (single thread). - Use AtomicInteger or AtomicLong when multiple threads update the same counter. - Use LongAdder for high-contention counters (many threads updating frequently). Key Java options include: - AtomicInteger.incrementAndGet() for a simple, correct, and common solution. - LongAdder.increment() for often better throughput under heavy contention. - Use synchronized or Lock when increments are part of a larger critical section. Remember, volatile does not make ++ safe; it only aids with visibility, not atomicity.

CodingToday Write a java program whether the given String is valid parentheses or not? public class validParentheses{ public static void main(String args[]){ Scanner sc=new Scanner(System.in); String str=sc.next(); boolean result=isValid(str); System.out.println(result); } public static boolean isValid(String str){ Stack<Character> stack=new Stack<>(); for(char ch:str.toCharArray()){ if(ch=='(' || ch=='[' || ch=='{'){ stack.push(ch); } else if(ch==')' || ch=='}' || ch==']'){ if(stack.isEmpty()){ return false; } char top=stack.pop(); if((ch==')' && top!='(') || (ch=='}' && top!='{') || (ch==']' && top!='[')){ return false; } } } return stack.isEmpty(); } } #DSA #dailycoding #Consistency #JavaPrograms #InterviewPrep

#Coding10 👉 Q: Remove Duplicates from a Sorted Array (Two Pointer Technique – Java). Example: int[] arr = {1, 1, 2, 2, 3, 4, 4}; Output → {1, 2, 3, 4} Count → 4 ✅ Two Pointer Technique (Optimal – O(n), O(1)) static int removeDuplicates(int[] arr) { if(arr.length == 0) return 0; int j = 1; // pointer for next unique position for(int i = 1; i < arr.length; i++) { if(arr[i] != arr[i - 1]) { arr[j] = arr[i]; j++; } } return j; // number of unique elements } How It Works Since the array is already sorted, duplicates are adjacent i scans the array j tracks the position to place the next unique element When a new element is found → place it at index j Complexity Analysis • Time Complexity → O(n) • Space Complexity → O(1) (In-place solution) Two-pointer pattern is extremely powerful for array problems. #DSA #Java #Arrays #TwoPointers #ProblemSolving #InterviewPrep #LearningInPublic #LinkedInDSA

𝐀𝐬 𝐝𝐞𝐯𝐞𝐥𝐨𝐩𝐞𝐫𝐬, 𝐰𝐞 𝐝𝐨𝐧’𝐭 𝐣𝐮𝐬𝐭 𝐰𝐫𝐢𝐭𝐞 𝐜𝐨𝐝𝐞. 𝐖𝐞 𝐦𝐮𝐬𝐭 𝐮𝐧𝐝𝐞𝐫𝐬𝐭𝐚𝐧𝐝 𝐰𝐡𝐚𝐭 𝐡𝐚𝐩𝐩𝐞𝐧𝐬 𝐛𝐞𝐡𝐢𝐧𝐝 𝐭𝐡𝐞 𝐬𝐜𝐞𝐧𝐞𝐬. == vs .equals() in Java. At first glance, they look similar. But they check completely different things. == ------->Compares references (memory location) .equals() ----->Compares actual content Example: String s1 = "Java"; String s2 = "Java"; String s3 = new String("Java"); System.out.println(s1 == s2); // true System.out.println(s1 == s3); // false System.out.println(s1.equals(s3)); // true Why? ✔ s1 and s2 point to the same object in the String Constant Pool ✔ s3 creates a new object in the heap ✔ .equals() checks character-by-character content(not the reference) This small difference can cause BIG bugs, especially when working with Strings, Objects, or Collections. Understanding memory behavior > Memorizing syntax. #Java #Programming #LearningInPublic #dailyChallenge

It’s easy to forget how much chaos Java had before generics… until you look at code that still relies on raw types. Once you see how type parameters actually shape safety and structure in collections, it becomes obvious why this feature changed everything. If you want a clean walkthrough of the fundamentals that many devs gloss over, this article lays it out clearly. https://bit.ly/4rlvIbG

𝐇𝐨𝐰 𝐭𝐨 𝐑𝐞𝐚𝐝 𝐚𝐧𝐝 𝐏𝐫𝐢𝐧𝐭 𝐚𝐧 𝐈𝐧𝐭𝐞𝐠𝐞𝐫 𝐕𝐚𝐥𝐮𝐞 𝐢𝐧 𝐉𝐚𝐯𝐚 𝐔𝐬𝐢𝐧𝐠 𝐒𝐜𝐚𝐧𝐧𝐞𝐫 𝐂𝐥𝐚𝐬𝐬 The Scanner class in java.util package is the easiest way to take input from the user in Java. It reads data from various input sources, including the keyboard. 𝐈𝐦𝐩𝐨𝐫𝐭 𝐃𝐞𝐜𝐥𝐚𝐫𝐚𝐭𝐢𝐨𝐧: 𝘪𝘮𝘱𝘰𝘳𝘵 𝘫𝘢𝘷𝘢.𝘶𝘵𝘪𝘭.𝘚𝘤𝘢𝘯𝘯𝘦𝘳 𝐒𝐭𝐞𝐩𝐬 𝐭𝐨 𝐑𝐞𝐚𝐝 𝐚𝐧𝐝 𝐏𝐫𝐢𝐧𝐭 𝐚𝐧 𝐈𝐧𝐭𝐞𝐠𝐞𝐫 𝐮𝐬𝐢𝐧𝐠 𝐚 𝐒𝐜𝐚𝐧𝐧𝐞𝐫 ➟ Import the Scanner class. ➟ Create a Scanner object to read input. ➟ Prompt the user for input. ➟ Read the integer using nextInt(). ➟ Print the integer using System.out.println(). ▓▒░▓▒░▓▒░▓▒░▓▒░▓▒░▓▒░ 𝐄𝐱𝐚𝐦𝐩𝐥𝐞: 𝘪𝘮𝘱𝘰𝘳𝘵 𝘫𝘢𝘷𝘢.𝘶𝘵𝘪𝘭.𝘚𝘤𝘢𝘯𝘯𝘦𝘳; 𝘱𝘶𝘣𝘭𝘪𝘤 𝘤𝘭𝘢𝘴𝘴 𝘎𝘍𝘎{  𝘱𝘶𝘣𝘭𝘪𝘤 𝘴𝘵𝘢𝘵𝘪𝘤 𝘷𝘰𝘪𝘥 𝘮𝘢𝘪𝘯(𝘚𝘵𝘳𝘪𝘯𝘨[] 𝘢𝘳𝘨𝘴){   // 𝘚𝘵𝘦𝘱 1: 𝘊𝘳𝘦𝘢𝘵𝘦 𝘚𝘤𝘢𝘯𝘯𝘦𝘳 𝘰𝘣𝘫𝘦𝘤𝘵   𝘚𝘤𝘢𝘯𝘯𝘦𝘳 𝘴𝘤 = 𝘯𝘦𝘸 𝘚𝘤𝘢𝘯𝘯𝘦𝘳(𝘚𝘺𝘴𝘵𝘦𝘮.𝘪𝘯);   // 𝘚𝘵𝘦𝘱 2: 𝘗𝘳𝘰𝘮𝘱𝘵 𝘶𝘴𝘦𝘳 𝘧𝘰𝘳 𝘪𝘯𝘱𝘶𝘵   𝘚𝘺𝘴𝘵𝘦𝘮.𝘰𝘶𝘵.𝘱𝘳𝘪𝘯𝘵("𝘌𝘯𝘵𝘦𝘳 𝘢𝘯 𝘪𝘯𝘵𝘦𝘨𝘦𝘳: ");   // 𝘚𝘵𝘦𝘱 3: 𝘙𝘦𝘢𝘥 𝘪𝘯𝘵𝘦𝘨𝘦𝘳 𝘪𝘯𝘱𝘶𝘵   𝘪𝘯𝘵 𝘯𝘶𝘮𝘣𝘦𝘳 = 𝘴𝘤.𝘯𝘦𝘹𝘵𝘐𝘯𝘵();   // 𝘚𝘵𝘦𝘱 4: 𝘗𝘳𝘪𝘯𝘵 𝘵𝘩𝘦 𝘦𝘯𝘵𝘦𝘳𝘦𝘥 𝘪𝘯𝘵𝘦𝘨𝘦𝘳   𝘚𝘺𝘴𝘵𝘦𝘮.𝘰𝘶𝘵.𝘱𝘳𝘪𝘯𝘵𝘭𝘯("𝘠𝘰𝘶 𝘦𝘯𝘵𝘦𝘳𝘦𝘥: " + 𝘯𝘶𝘮𝘣𝘦𝘳);   // 𝘊𝘭𝘰𝘴𝘦 𝘵𝘩𝘦 𝘴𝘤𝘢𝘯𝘯𝘦𝘳   𝘴𝘤.𝘤𝘭𝘰𝘴𝘦();  } } ▓▒░▓▒░▓▒░▓▒░▓▒░▓▒░▓▒░▓▒░ 𝐎𝐮𝐭𝐩𝐮𝐭: Enter an integer: 123 You entered: 123 ...Program finished with exit code 0 Press ENTER to exit console. 𝐄𝐱𝐩𝐥𝐚𝐧𝐚𝐭𝐢𝐨𝐧: ➟ Scanner sc = new Scanner(System.in); -> Creates a Scanner object to take input. ➟ nextInt() -> Reads an integer value entered by the user. ➟ System.out.println() -> Prints the entered integer on the screen. #Java #PrintanInteger #ScannerClass #String #JAVAEXPLANATIONS #JAVAExamples #Coding #Developer #CodeLife #Programmer #AshokIT

🚀 Java 8 Streams – A Small Problem That Tests Big Concepts Today I revisited a classic interview question that seems simple but hides some heavy duty concepts: 👉 Find the last repeating character in a string using Java 8 Streams. Example: Input: "programming" Output: g (The repeated chars are 'r', 'g', 'm'. 'g' is the last one to appear in the original sequence.) Here is an elegant way to solve it: Java String input = "programming"; Optional<Character> result = input.chars() .mapToObj(c -> (char) c) .collect(Collectors.groupingBy( Function.identity(), LinkedHashMap::new, // Key: Maintains insertion order Collectors.counting() // Value: Frequency count )) .entrySet() .stream() .filter(e -> e.getValue() > 1) .reduce((first, second) -> second) // The "Last" logic .map(Map.Entry::getKey); result.ifPresent(System.out::println); ✨ Why this is a great test of fundamentals: It’s not just about the syntax it’s about what’s happening under the hood: It’s easy to write code that works it’s harder to write code that is both expressive and efficient. I’m curious how would you tackle this 😄? 1️⃣ Stick to the modern Streams approach? 2️⃣ Go back to a traditional for loop for potential performance gains? 3️⃣ Use a different collection entirely? #Java #Java8 #Streams #BackendDevelopment #CodingInterview #SoftwareEngineering #CleanCode #InterviewQuestion

🔹 Discussion Topic: Why For-Each Loop Cannot Modify Elements 💬 Discussion Topic: Understanding how for-each works under the hood and why it’s read-only for primitives Imagine iterating over arrays or collections in a Java program: You want to traverse elements quickly You might expect to modify values directly during iteration 🔹 How For-Each Works Automatically iterates over arrays or any Iterable collection For primitives, the loop variable stores a copy of the element For objects, the loop variable stores a reference to the object Internally uses index-based access for arrays and Iterator for collections 🔹 Why Modification Doesn’t Work Primitives: Changing the loop variable modifies only the copy, not the original element Objects: You can change the state of the object, but you cannot replace the object itself in the array or collection References: Reassigning the loop variable affects only the temporary reference, leaving the collection unchanged ❌ Cannot directly modify array elements or collection elements ❌ Cannot delete or replace elements ✅ Correct Approach For modifying primitives in arrays → use index-based loops For modifying or deleting elements in collections → use Iterator methods 💡 Pro Tip: Use for-each for reading/traversing only Always remember the difference between copy vs reference This knowledge prevents subtle bugs in production code

𝐃𝐚𝐲 𝟗 – 𝐑𝐞𝐯𝐢𝐬𝐢𝐭𝐢𝐧𝐠 𝟐-𝐃 𝐀𝐫𝐫𝐚𝐲𝐬 𝐢𝐧 𝐉𝐚𝐯𝐚 One important realization: 👉 In Java, a 2-D array is NOT actually a “matrix”. It is an array of arrays. That means: Each row is a separate array object. Rows can have different lengths. Memory is not necessarily continuous like in C/C++ Example: int[][] arr = new int[3][]; arr[0] = new int[2]; arr[1] = new int[4]; arr[2] = new int[3]; This is called a 𝑱𝒂𝒈𝒈𝒆𝒅 𝑨𝒓𝒓𝒂𝒚. Many beginners assume: arr.length == total elements ❌ But actually: arr.length → number of rows arr[i].length → number of columns in that specific row This small understanding prevents many traversal bugs. The deeper you understand memory structure, the cleaner your logic becomes. 🔹 Beginner Level 2-D Array Problems : These are simple but build strong fundamentals. 1️⃣ Print a 2D array----> Traverse and print all elements. 2️⃣ Find the sum of all elements 3️⃣ Row-wise sum-----> Print sum of each row separately. 4️⃣ Column-wise sum---->This helps understand traversal direction change. 5️⃣ Find the largest element----> Simple scanning problem. #Java #DataStructures #LearningInPublic #dailyChallenge