Return List of Interface in Java-CodePudding

I have to create a word counter program. It is not very difficult logically but I am getting stuck with interfaces. So first I have to create an class which implements the defined interface:

public interface WordFrequency {
String getWord();
int getFrequency();
}

And I have to create another class which implements another interface as defined:

public interface WordFrequencyAnalyzer {
int calculateHighestFrequency(String text);
int calculateFrequencyForWord (String text, String word);
List<WordFrequency> calculateMostFrequentNWords (String text, int n);
}

Now, the third method in this interface returns a list of the previous interface. I will maintain the frequencies of words in a Map. This method requires me to return the words with N highest frequencies in the given text. It would be very easy to just sort the map with descending values and return accordingly, but how do I create a list of this particular interface with the correct values from the map to return in the required format?

Edit: I am using Map<String,Integer> m = new HashMap<String,Integer>() to store the words and their frequencies. This is what I need to store in List<WordFrequency> and return.

CodePudding user response：

You can consider this example as a starting point for your use case:

interface

public interface WordFrequency {
    String getWord();
    int getFrequency();
}

The implementation of above interface

public class WordFreqImpl implements WordFrequency {

    final String w;
    final Integer f;

    public WordFreqImpl(String word, Integer freq) {
        w = word;
        f = freq;

    }
    @Override
    public String getWord() {
        return w;
    }

    @Override
    public int getFrequency() {
        return f;
    }

    @Override
    public String toString() {
        return ""  
                "w="   w  
                ", f="   f;
    }
}

demo of getting the list per your requirement

public class WordFreqDemo {
    public static void main(String[] args) {
        Map<String,Integer> m = new HashMap<>();
        m.put("k1",1);
        m.put("k2",2);
        m.put("k3",3);

        List<WordFrequency> wordFrequencyList = new ArrayList<>();

        for (Map.Entry<String, Integer> entry: m.entrySet()) {
            wordFrequencyList.add(new WordFreqImpl(entry.getKey(), entry.getValue()) {
            });
        }

        for (WordFrequency w: wordFrequencyList) {
            System.out.println(w);
        }
        
        // return wordFrequencyList as per use case
    }
}

output

w=k1, f=1
w=k2, f=2
w=k3, f=3

CodePudding user response：

Simply, you must have an concrete object that implements the interface. Then you can add that object to your list because it will now be a WordFrequency object in addition to whatever object it is by default. You will also need an object that implements the WordFrequencyAnalyzer interface as well.

The interface is a contract which guarantees that any object implementing the interface will have certain behaviors. It abstracts the implementation away and allows objects to be more polymorphic.

This is a good resources on interfaces

https://www.geeksforgeeks.org/interfaces-in-java/

CodePudding user response：

Still an answer showing record as ad-hoc data class, and Stream-.

The n highest frequency entries from the map:

record Fr(String word, int frequency) implements WordFrequency {
    @Override
    public String getWord() {
       return word;
    }
    @Override
    public int getFrequency() {
        return frequency;
    }
}

Map<String,Integer> m = ...
List<WordFrequency> wfs = m.entrySet().stream()
    .sorted(e -> Comparator.comparingInt(e.getValue()).reversed()
                           .thenComparing(e.getKey()))
    .limit(n)
    .map(e -> new Fr(e.getKey(), e.getValue())
    .collect(Collectors.toList()):