Initializing a HashMap with default values?

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I'm implementing the A* search algorithm given here,*_search_algorithm

This line indicates we need to initiliaze a map with the default values of INFINITY,

gScore := map with default value of Infinity

So I tried that here,

Map<State, Double> gScore = new HashMap<State, Double>(Double.POSITIVE_INFINITY);

This does not work however the following does;

Map<State, Double> gScore = new HashMap<State, Double>((int) Double.POSITIVE_INFINITY);

I'm wondering why, and what impact (if any) it will have on my implementation.

There is no way to initialize a map with a default value in Java, and your second version will not create a map with a default value of infinity, but instead will try to create an infinitely large map. (Not really, but it'll try creating the largest map possible.)

Instead, modify the algorithm: anytime you do map.get(key), check if the value is null and, if so, replace it with infinity.

Java HashMap Inline Initialization, The Imperative Way of Initializing a HashMap​​ The straight forward solution is to declare a Map and then just put() entries into the Map. We will use this example as reference to compare with other techniques that are more type saving. Map<String,String> mymap = new HashMap<String, String>(); test. put("A","one"); test. HashMap is a part of java.util package.HashMap extends an abstract class AbstractMap which also provides an incomplete implementation of Map interface. It stores the data in (Key, Value) pairs. We can initialize HashMap using the constructor in four different ways : 1.HashMap() It is the default constructor with initial capacity 16 and load factor 0.75.

How to directly initialize a HashMap (in a literal way)?, All Versions. In case you happen to need just a single entry: There is Collections.​singletonMap("key", "value") . For Java Version 9 or higher: Yes, this is possible  The Static Initializer for a static HashMap. We can initialize a HashMap using a static block of code: The advantage of this kind of initialization is that the map is mutable but it will work only for static. Entries could be added and removed as and when required.

Instead of explicitly putting Double.POSITIVE_INFINITY for all the possible keys (which may be inefficient), you can use putIfAbsent.

In any place where you have:

value = map.get(key);

you can change it to:

value = map.putIfAbsent(key,Double.POSITIVE_INFINITY);

This will behave as if the value of any key not present in the Map (or any key whose current value is null) is Double.POSITIVE_INFINITY. It will put the value Double.POSITIVE_INFINITY in the Map for any such keys.

It will save you the need to check if map.get(key) returns null.

Initialize HashMap in Java, Initialize HashMap in Java. 1.HashMap() It is the default constructor with initial capacity 16 and load factor 0.75. 2.HashMap(int initialCapacity) It is used to create an empty HashMap object with specified initial capacity under default load factor 0.75. 3.HashMap(int initial capacity, float loadFactor) 4.HashMap(Map This creates an anonymous subclass of HashMap, whose instance initializer puts these values. In other words it creates a new class that inherits from HashMap. This is the shortest way to create and initialize a dynamic HashMap. Map<Integer, String> mymap = new HashMap<Integer, String>() { { put(1, "one"); put(2, "two"); } };

What Are Initial Capacity And Load Factor Of HashMap In Java?, Well, there is an idiom called double brace initialization, which you can use to initialize the HashMap at the time of declaration. I'll show you how to use that double  This article describes the need to initialize a HashMap with fitting default values. It is important to know something about the internal implementation of a HashMap to select the best default values for initialization.

How to initialize HashMap with values in Java? One liner, To initialize a HashMap after the creation time, you can use put, Java 8+ putIfAbsent("k3", 3); // Can add null key and value map. When you create and initialize a new HashMap by using the default constructor HashMap(),  HashMap Construction with initial values . Benjamin Samuel. eg override default HashMap toString() If you want to load key-value pairs from some other source

Initialize a HashMap in Java, In this post, we will discuss various methods to initialize map in Java. Map<​String, String> hm = new HashMap<String, String>(); There are existing factories in the Collections class to produce singleton Map that have exactly one key-value  Initializing HashSet in Java Set in Java is an interface which extends Collection. It is an unordered collection of objects in which duplicate values cannot be stored.