Bits Manipulation in Java

1. Detect if two integers have opposite signs. 2. Determining if an integer is a power of 2. 3. Swap the values of a and b without using a temporary variable. 4. Check non-zero. References: Gayle Laakmann Mcdowell, “Bit Manipulation”, in Cracking the code interview, 6th Edition. Bit Twiddling Hacks, Accessed at https://graphics.stanford.edu/~seander/bithacks.html Bit Manipulation… Read More »

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Maps in Java

Concrete maps in Java JDK 1.8 Below is the summary of differences between HashMap, LinkedHashMap, TreeMap, and Hashtable in Java: (Source: javarevisited.blogspot.com) If we need to get the key back in insertion order, then use LinkedHashMap. If we need to get the key back in their true/natural order, then use TreeMap. Otherwise, HashMap is best because it… Read More »

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Binary search algorithm

1. Getting. In binary search algorithm, we find an element x in a sorted array by using the principle of divide and conquer. First, we compare x to the middle point of the array. If x is less than the middle point, then we search the left of array. Otherwise, we look for the right… Read More »

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Singleton Pattern

1. Definition. Singleton Pattern makes sure that a class only have one instance and provide a global point of access to it. It also belongs to Creation Pattern Group. Singleton Pattern should be used where we only need one of: Thread pools, caches, dialog boxes, object that handle preferences and registry settings, objects used of… Read More »

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Observer Pattern

Observer Pattern defines a one-to-many relationship between a set of objects. When the state of one object changes, all of its dependents are notified/updated automatically. It also belongs to Behavior pattern group. 1. A customized notification system. Several newspaper agencies like CNN, NYTime, BBC are subscribed to a feed of new tweets and may want… Read More »

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Hibernate cache in theory

The note will follow: 1. Introduction. Hibernate has a two-level cache architecture: first-level cache and second-level cache. Figure 1: Hibernate’s two levels cache (source: Manning) The first-level cache is the persistence context cache (scope of Session). The cache ensures that when the application requests the same persistent object twice in a particular session, it gets back… Read More »

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