HashMaps

import java.util.HashMap;

class Main {
    public static void main(String[] args) {
        HashMap<String, Integer> examScores = new HashMap<String, Integer>();

        examScores.put("Math", 75); // put something into a hashmap
        examScores.put("English", 86);
        examScores.put("Psychology", 100);

        examScores.putIfAbsent("Science", 66); // add Science, since it doesn't exist in our hashmap

        examScores.replace("English", 70); // updates the value of the English key

        examScores.clear(); // clear the hashmap

        examScores.remove("Math"); // removes the key-value pair for Math

        System.out.println(examScores.toString()); // print out a hashmap
        System.out.println(examScores.get("English")); // print out the value for a single key
        System.out.println(examScores.getOrDefault("Religion", -1)); // return the value of the Religion key, else -1 if it doesn't exist
        System.out.println(examScores.size()); // prints the length of the examScores hashmap
        System.out.println(examScores.containsKey("Math")); // returns true if the key exists
        System.out.println(examScores.containsValue(100)); // returns true if the value exists
        System.out.println(examScores.isEmpty()); // returns true if the hashmap is empty
    }
}

class Main {
    public static void main(String[] args) {
        HashMap<String, Integer> examScores = new HashMap<String, Integer>();

        examScores.put("Math", 75);
        examScores.put("English", 86);
        examScores.put("Psychology", 100);

        examScores.forEach((subject, score) -> {
            System.out.println(subject + "-" + score);
            examScores.replace(subject, score - 10);
        });
        System.out.println(examScores.toString());
    }
}