12/7/2023 0 Comments Hashmap java examplesIterating over HashMap’s entrySet with foreach loop Iterating over HashMap’s entrySet with foreach and lambda Iterating over HashMap’s entrySet with iterator Iterating over HashMap’s keyset() with foreach and lambda: Iterating over HashMap using keyset() with foreach loop: Iterating over HashMap with foreach and lambda: Public HashMap(Map m): This constructor is used when you want to create HashMap from some other Map such as TreeMap or LinkedHashMap. In most of the scenarios, you should avoid using this constructor unless you are sure about this as load factor 0.75 provides a good tradeoff between time and space. Public HashMap(int initialCapacity,float loadFactor): This constructor is used to specify initial capacity of the HashMap and load factor. Public HashMap(int initialCapacity): This constructor is used to specify the initial capacity of HashMap and default load factor 0.75. It creates an empty HashMap with default initial capacity of 16 and load factor 0.75. Public HashMap(): This is the default constructor and used mostly. Yes, Just to make things more obvious, HashMap implements Map interface again and there is nothing wrong in implementing interface again.You don’t have to go through class Hierarchy to find it out that HashMap implements Map interface. (entry.getKey() + " = " +entry.Did you notice HashMap implements Map interface even if AbstractMap already implements it? (entry.getKey() + " = " +entry.getValue()) In the following example, we can observe that the elements of the HashMap is in random order while the elements of the TreeMap is arranged in ascending order. The TreeMap should be used when we require key-value pair in sorted (ascending) order. The HashMap should be used when we do not require key-value pair in sorted order. The elements are sorted in natural order (ascending). TreeMap class is rich in functionality, because it contains functions like: tailMap(), firstKey(), lastKey(), pollFirstEntry(), pollLastEntry(). HashMap class contains only basic functions like get(), put(), KeySet(), etc. It uses the compareTo() method to compare keys. The equals() method of Map class overrides it. It uses equals() method of the Object class to compare keys. TreeMap internally uses a Red-Black tree, which is a self-balancing Binary Search Tree. TreeMap is slow in comparison to HashMap because it provides the performance of O(log(n)) for most operations like add(), remove() and contains(). HashMap is faster than TreeMap because it provides constant-time performance that is O(1) for the basic operations like get() and put(). TreeMap allows homogeneous values as a key because of sorting. HashMap allows heterogeneous elements because it does not perform sorting on keys. TreeMap does not allow null keys but can have multiple null values. HashMap allows a single null key and multiple null values. TreeMap implements NavigableMap, Cloneable, and Serializable interface. HashMap implements Map, Cloneable, and Serializable interface. Java TreeMap is a Tree structure-based implementation of Map interface. Java HashMap is a hashtable based implementation of Map interface. The following table describes the differences between HashMap and TreeMap. HashMap does not preserve the iteration order while the TreeMap preserve the order by using the compareTo() method or a comparator set in the TreeMap's constructor. The Key difference between HashMap and TreeMap is: The iterator throws a ConcurrentModificationException if the map gets modify in any way.Map use put() method to add an element in the map.Both classes represents the mapping from key to values.In the key-value pair, each key is unique, but their values may be duplicate. A Map is an object which stores key-value pairs.Both the classes extend AbstractMap class.HashMap and TreeMap classes implement Cloneable and Serializable interface.It stores the object in the tree structure.It cannot have a null key but have multiple null values.TreeMap also contains value based on the key.It is implemented by the Red-Black tree, which means that the order of the keys is sorted. TreeMap class extends AbstractMap class and implements NavigableMap, Cloneable, and Serializable interface. HashMap does not maintain order while iterating.It may have a single null key and multiple null values.HashMap contains value based on the key.HashMap implements Map, Cloneable and Serializable interface. When buckets get too large, they get transformed into nodes of TreeNodes, each structured similarly to those in. Java Map implementation usually acts as a bucketed hash table. Java HashMap and TreeMap both are the classes of the Java Collections framework. Next → ← prev Difference between HashMap and TreeMap
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