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Use‑Level Lock Optimization Reduce Lock Holding Time Code that does not require synchronization should be kept outside the critical section so that the lock is released as quickly as possible. Reduce Lock Granularity The idea is to split a single physical lock into multiple logical locks, increasing parallelism and reducing contention. This is ...

Advanced Collection Framework Understanding Map Collections Map collections in Java have several distinctive characteristics: They store data in key-value pairs, requiring both elements for each entry Keys must be unique while values can be duplicated Each key maps to exactly one value, creating a one-to-one relationship The combined key-value ...

JDK Bug Analysis This article discusses a subtle issue discovered in JDK 8 related to the computeIfAbsent method within ConcurrentHashMap. Discovery Process The issue came to light while reviewing changes in Apache Dubbo 2.7.7. A specific bug fix was noted: JDK-8062841: Deadlock in ConcurrentHashMap.computeIfAbsent when keys have identical has ...

1. Method-Level Isolation via Thread Confinement A robust strategy involves confining the HashMap instance to the execution scope of a single thread. In typical web server architectures, such as those built on Tomcat, incoming requests trigger a chain of operations involving controllers and services. Within the service layer method, a developer ...

HashMap is one of the most widely used collections in Java applications, primarily for storing key-value pairs with efficient lookup performance. To understand its inner workings, we explore how it manages data storage, resolves collisions, handles resizing, and why it is not thread-safe. Class Hierarchy and Core Interfaces HashMap implements s ...

---------------🎈🎈 LeetCode Problem 49: Group Anagrams 🎈🎈------------------- In Java, arrays cannot be used directly as keys in a HashMap because their hashCode() method does not reflect the actual content. It is therefore recommended to use immutable objects such as strings as keys. Approach 1: Use a Sorted String as the Key ⭐️ Since two ...

Display Table Given an array of orders where each element contains a customer name, table number, and food item, return a display table showing how many of each dish was ordered at each table. The table should have "Table" as the first column header, followed by alphabetical sorted food item names. Each row represents a table with its ...

HashMap Core Characteristics HashMap implements key-value storage using hash tables, offering non-thread-safe operations. Both keys and values can be null, and entries are unordered. Pre-JDK 1.8, HashMap used array-chaining (linked lists) to resolve collisions. Since JDK 1.8, when bucket chains exceed 8 elements and the array size surpasses 64, ...

Overview of Java Thread-Safe Classes Class Type Characteristics Description Legacy Thread-Safe Classes Uses synchronized for thread safety Deprecated classes like Stack, Vector, Hashtable Collections-Decorated Classes Wrapper classes using synchronized Thread-safe versions of standard collections JUC Classes Uses CAS and multiple loc ...

Two Sum Given an array of integers nums and a target value target, find the indices of two numbers that add up to target. Return the indices as a pair. Solution 1: Brute Force class Solution { public int[] twoSum(int[] nums, int target) { for (int i = 0; i < nums.length; i++) { for (int j = i + 1; j < nums.lengt ...