EnumSet และ EnumMap

EnumSet และ EnumMap

EnumSet: การสร้างเซต

import java.util.*;

enum Day { MON, TUE, WED, THU, FRI, SAT, SUN }

EnumSet<Day> weekdays  = EnumSet.range(Day.MON, Day.FRI);
EnumSet<Day> weekend   = EnumSet.of(Day.SAT, Day.SUN);
EnumSet<Day> allDays   = EnumSet.allOf(Day.class);
EnumSet<Day> noDays    = EnumSet.noneOf(Day.class);

System.out.println(weekdays); // [MON, TUE, WED, THU, FRI]
System.out.println(weekend);  // [SAT, SUN]
System.out.println(allDays.size()); // 7

EnumSet: การดำเนินการกับเซต

import java.util.*;

enum Permission { READ, WRITE, DELETE, ADMIN, EXPORT }

EnumSet<Permission> userPerms  = EnumSet.of(Permission.READ, Permission.WRITE);
EnumSet<Permission> adminPerms = EnumSet.allOf(Permission.class);

// Complement
EnumSet<Permission> missing = EnumSet.complementOf(userPerms);
System.out.println("Missing: " + missing);
// Missing: [DELETE, ADMIN, EXPORT]

// Intersection (retain)
EnumSet<Permission> shared = EnumSet.copyOf(userPerms);
shared.retainAll(adminPerms);
System.out.println("Shared: " + shared); // [READ, WRITE]

EnumMap: การจับคู่อีนัมกับค่า

import java.util.*;

enum Quarter { Q1, Q2, Q3, Q4 }

EnumMap<Quarter, Double> revenue = new EnumMap<>(Quarter.class);
revenue.put(Quarter.Q1, 125_000.0);
revenue.put(Quarter.Q2, 148_500.0);
revenue.put(Quarter.Q3, 132_750.0);
revenue.put(Quarter.Q4, 175_200.0);

double total = revenue.values().stream()
    .mapToDouble(Double::doubleValue).sum();
System.out.printf("Annual revenue: $%.0f%n", total);
// Annual revenue: $581450

EnumMap: การวนซ้ำตามลำดับ

import java.util.*;

enum Month { JAN, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC }

EnumMap<Month, Integer> salesUnits = new EnumMap<>(Month.class);
salesUnits.put(Month.MAR, 1420);
salesUnits.put(Month.JAN, 980);
salesUnits.put(Month.FEB, 1105);

// Iterates JAN, FEB, MAR (declaration order, not insertion order)
for (var entry : salesUnits.entrySet()) {
    System.out.println(entry.getKey() + ": " + entry.getValue());
}
// JAN: 980
// FEB: 1105
// MAR: 1420

ระบบสิทธิ์ด้วย EnumSet

import java.util.*;

enum Permission { READ, WRITE, DELETE, PUBLISH, ADMIN }

record Role(String name, EnumSet<Permission> permissions) {
    boolean can(Permission p) { return permissions.contains(p); }
}

Role editor = new Role("Editor",
    EnumSet.of(Permission.READ, Permission.WRITE, Permission.PUBLISH));
Role viewer = new Role("Viewer",
    EnumSet.of(Permission.READ));

System.out.println(editor.can(Permission.WRITE));  // true
System.out.println(viewer.can(Permission.DELETE)); // false

แฟล็กฟีเจอร์ด้วย EnumMap

import java.util.*;

enum Feature { DARK_MODE, BETA_EDITOR, AI_SUGGESTIONS, EXPORT_PDF }

class FeatureFlags {
    private final EnumMap<Feature, Boolean> flags = new EnumMap<>(Feature.class);

    public FeatureFlags() {
        for (Feature f : Feature.values()) flags.put(f, false);
    }

    public void enable(Feature f)  { flags.put(f, true); }
    public void disable(Feature f) { flags.put(f, false); }
    public boolean isEnabled(Feature f) { return flags.getOrDefault(f, false); }
}

FeatureFlags ff = new FeatureFlags();
ff.enable(Feature.DARK_MODE);
System.out.println(ff.isEnabled(Feature.DARK_MODE));      // true
System.out.println(ff.isEnabled(Feature.AI_SUGGESTIONS)); // false

ประสิทธิภาพ: EnumSet เทียบกับ HashSet

import java.util.*;

enum Day { MON, TUE, WED, THU, FRI, SAT, SUN }

// EnumSet: bit operations on a long value
EnumSet<Day> workDays = EnumSet.range(Day.MON, Day.FRI);

// HashSet: hash table with boxing overhead
Set<Day> hashWorkDays = new HashSet<>(Arrays.asList(
    Day.MON, Day.TUE, Day.WED, Day.THU, Day.FRI));

// Both work, but EnumSet is ~5x faster for contains/add/remove
// and uses less memory
System.out.println(workDays.contains(Day.SAT));     // false
System.out.println(workDays.contains(Day.MON));     // true

getOrDefault และ computeIfAbsent ของ EnumMap

import java.util.*;

enum Category { FOOD, ELECTRONICS, CLOTHING, BOOKS }

EnumMap<Category, List<String>> catalog = new EnumMap<>(Category.class);

// computeIfAbsent creates the list on first use
catalog.computeIfAbsent(Category.BOOKS, k -> new ArrayList<>()).add("Clean Code");
catalog.computeIfAbsent(Category.BOOKS, k -> new ArrayList<>()).add("Effective Java");
catalog.computeIfAbsent(Category.ELECTRONICS, k -> new ArrayList<>()).add("Laptop");

System.out.println(catalog.get(Category.BOOKS));
// [Clean Code, Effective Java]
System.out.println(catalog.getOrDefault(Category.FOOD, List.of()));
// []

รูปแบบมัลติแมปด้วย EnumMap

import java.util.*;
import java.util.stream.*;

enum Priority { LOW, NORMAL, HIGH, URGENT }
record Task(String name, Priority priority) {}

List<Task> tasks = List.of(
    new Task("Fix login bug", Priority.URGENT),
    new Task("Update docs",   Priority.LOW),
    new Task("Add unit tests",Priority.NORMAL),
    new Task("Deploy hotfix", Priority.URGENT)
);

// Group by priority into EnumMap
EnumMap<Priority, List<Task>> byPriority = tasks.stream()
    .collect(Collectors.groupingBy(Task::priority,
        () -> new EnumMap<>(Priority.class),
        Collectors.toList()));

byPriority.forEach((p, ts) ->
    System.out.println(p + ": " + ts.stream().map(Task::name).collect(Collectors.joining(", "))));

ควรใช้ EnumSet หรือ EnumMap เมื่อใด

ตรวจสอบความเข้าใจ

สรุปทบทวน: EnumSet และ EnumMap