ListIterator vs Iterator in Java

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An Iterator can iterate in only one direction (forward direction), whereas ListIterator can iterate in both forward and back directions. We can add or set a value at any time in the lifespan of the ListIterator. ListIterator maintains two pointers viz. previous and next. An Iterator can be used to iterate over a list, set, or map structure. But a ListIterator is only used to iterate through a list. For example Set<Integer> mSet = new HashSet<Integer>(); mSet.add(0); mSet.add(1); Iterator<Integer> mSetIterator = mSet.iterator(); // we cannot do Iterator<Integer> mSetIterator = mSet.listIterator(); List<Integer> mList = new ArrayList<Integer>(); mList.add(0); mList.add(1); // following two statements are valid for listRead More →

CopyOnWriteArrayList vs ArrayList in Java

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CopyOnWriteArrayList and the ArrayList are part of the Collections framework. CopyOnWriteArrayList and ArrayList implement the List interface (just like Vector and LinkedList), but underlying implementations either support multi-threaded applications or single threaded applications. In CopyOnWriteArrayList, each mutative operation e.g. add, set etc are done after creating a copy of the underlying array. Since it uses a ‘snapshot’ style iterator and copy never changes for the lifetime of the iterator, it does not get a ConcurrentModificationException. In this lifetime, any modifications on the original one will not be available to that iterator which is working on the copy. You cannot use its iterator to do mutations otherwiseRead More →

ConcurrentHashMap vs HashTable in Java

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ConcurrentHashMap uses multiple buckets to store data. Since HashTable locks the whole map, ConcurrentHashMap does not come with a performance impact as seen in HashTable (due to having multiple locks at the segment level (sharding) rather than the object level). ConcurrentHashMap and HashTable are thread-safe. The main difference lies in their performance. ConcurrentHashMap has a good performance than HashTable. I found a very helpful analogy online that says that HashTable provides the lock on the main door of your house, while ConcurrentHashMap locks each door within your house. You cannot do compound operations on ConcurrentHashMap, but they are supported in HashTable (due to them havingRead More →