Map dan Penghitungan Frekuensi

Apa itu Peta?

Operasi umum

Kode: dasar-dasar Peta

public class Main {
  public static void main(String[] args) {
    java.util.Map<String, Integer> scores = new java.util.HashMap<>();
    scores.put("Ada", 90);
    scores.put("Bob", 75);
    scores.put("Ada", 95); // replaces old value

    System.out.println("Bob's score=" + scores.get("Bob"));
    System.out.println("Has Ada? " + scores.containsKey("Ada"));
    scores.remove("Bob");

    for (java.util.Map.Entry<String, Integer> e : scores.entrySet()) {
      System.out.println(e.getKey() + " -> " + e.getValue());
    }
  }
}

Gagasan frekuensi

Kode: frekuensi kata

public class Main {
  public static void main(String[] args) {
    String[] words = { "to", "be", "or", "not", "to", "be" };
    java.util.Map<String,Integer> counter = new java.util.HashMap<>();

    for (String w : words) {
      int newVal = counter.getOrDefault(w, 0) + 1;
      counter.put(w, newVal);
    }
    System.out.println(counter);
  }
}

Kode: TreeMap terurut

public class Main {
  public static void main(String[] args) {
    java.util.Map<String,Integer> counts = new java.util.HashMap<>();
    counts.put("banana",2);
    counts.put("apple",3);
    counts.put("cherry",1);

    java.util.Map<String,Integer> sorted = new java.util.TreeMap<>(counts);
    for (java.util.Map.Entry<String,Integer> e : sorted.entrySet()) {
      System.out.println(e.getKey() + " -> " + e.getValue());
    }
  }
}

Pemeriksaan HashMap

Ringkasan