I am new to java and practicing by creating a simplistic NaiveBayes classifier. I am still new to object instantiation, and wonder what to do to initialize a HashMap of HashMaps. When inserting new observations into the classifier, I can create a new HashMap for an unseen feature name in a given class, but do I need to initialize?
import java.util.HashMap;
public class NaiveBayes {
private HashMap<String, Integer> class_counts;
private HashMap<String, HashMap<String, Integer>> class_feature_counts;
public NaiveBayes() {
class_counts = new HashMap<String, Integer>();
// do I need to initialize class_feature_counts?
}
public void insert() {
// todo
// I think I can create new hashmaps on the fly here for class_feature_counts
}
public String classify() {
// stub
return "";
}
// Naive Scoring:
// p( c | f_1, ... f_n) =~ p(c) * p(f_1|c) ... * p(f_n|c)
private double get_score(String category, HashMap features) {
// stub
return 0.0;
}
public static void main(String[] args) {
NaiveBayes bayes = new NaiveBayes();
// todo
}
}
Note this question is not specific to Naive Bayes classifiers, just thought I would provide some context.
The Static Initializer for a Static HashMap We can also initialize the map using the double-brace syntax: Map<String, String> doubleBraceMap = new HashMap<String, String>() {{ put("key1", "value1"); put("key2", "value2"); }};
Initial Capacity of HashMap The initial capacity of the HashMap is the number of buckets in the hash table. It creates when we create the object of HashMap class. The initial capacity of the HashMap is 24, i.e., 16. The capacity of the HashMap is doubled each time it reaches the threshold.
Yes, you need to initialize it.
class_feature_counts = new HashMap<String, HashMap<String, Integer>>();
When you want to add a value to class_feature_counts, you need to instantiate it too:
HashMap<String, Integer> val = new HashMap<String, Integer>();
// Do what you want to do with val
class_feature_counts.put("myKey", val);
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