#10 effective java: item 3

effective-java/src/main/java/com/example/effectivejava/chapter01/item03/enumtype/Elvis.java

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+package com.example.effectivejava.chapter01.item03.enumtype;
+
+// 열거 타입 방식의 싱글턴 - 바람직한 방법 (25쪽)
+public enum Elvis {
+    INSTANCE;
+
+    public void leaveTheBuilding() {
+        System.out.println("기다려 자기야, 지금 나갈께!");
+    }
+
+    // 이 메서드는 보통 클래스 바깥(다른 클래스)에 작성해야 한다!
+    public static void main(String[] args) {
+        Elvis elvis = Elvis.INSTANCE;
+        elvis.leaveTheBuilding();
+    }
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item03/enumtype/EnumElvisReflection.java

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+package com.example.effectivejava.chapter01.item03.enumtype;
+
+import java.lang.reflect.Constructor;
+
+public class EnumElvisReflection {
+
+    public static void main(String[] args) {
+        try {
+            Constructor<Elvis> declaredConstructor = Elvis.class.getDeclaredConstructor();
+            System.out.println(declaredConstructor);
+        } catch (NoSuchMethodException e) {
+            e.printStackTrace();
+        }
+    }
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item03/enumtype/EnumElvisSerialization.java

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+package com.example.effectivejava.chapter01.item03.enumtype;
+
+import java.io.*;
+
+public class EnumElvisSerialization {
+
+    public static void main(String[] args) {
+        try (ObjectOutput out = new ObjectOutputStream(new FileOutputStream("elvis.obj"))) {
+            out.writeObject(Elvis.INSTANCE);
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+
+        try (ObjectInput in = new ObjectInputStream(new FileInputStream("elvis.obj"))) {
+            Elvis elvis = (Elvis) in.readObject();
+            System.out.println(elvis == Elvis.INSTANCE);
+        } catch (IOException | ClassNotFoundException e) {
+            e.printStackTrace();
+        }
+    }
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item03/functionalinterface/DefaultFunctions.java

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+package com.example.effectivejava.chapter01.item03.functionalinterface;
+
+import com.example.effectivejava.chapter01.item03.methodreference.Person;
+
+import java.time.LocalDate;
+import java.util.function.Consumer;
+import java.util.function.Function;
+import java.util.function.Predicate;
+import java.util.function.Supplier;
+
+public class DefaultFunctions {
+
+    public static void main(String[] args) {
+        Function<Integer, String> intToString = Object::toString;
+
+        Supplier<Person> personSupplier = Person::new;
+        Function<LocalDate, Person> personFunction = Person::new;
+
+        Consumer<Integer> integerConsumer = System.out::println;
+
+        Predicate<Person> predicate;
+    }
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item03/functionalinterface/MyFunction.java

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+package com.example.effectivejava.chapter01.item03.functionalinterface;
+
+@FunctionalInterface
+public interface MyFunction {
+
+    String valueOf(Integer integer);
+
+    static String hello() {
+        return "hello";
+    }
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item03/functionalinterface/UsageOfFunctions.java

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+package com.example.effectivejava.chapter01.item03.functionalinterface;
+
+import java.time.LocalDate;
+import java.util.ArrayList;
+import java.util.List;
+
+public class UsageOfFunctions {
+
+    public static void main(String[] args) {
+        List<LocalDate> dates = new ArrayList<>();
+        dates.add(LocalDate.of(1982, 7, 15));
+        dates.add(LocalDate.of(2011, 3, 2));
+        dates.add(LocalDate.of(2013, 1, 28));
+
+        List<Integer> before2000 = dates.stream()
+                .filter(d -> d.isBefore(LocalDate.of(2000, 1, 1)))
+                .map(LocalDate::getYear).toList();
+    }
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item03/methodreference/Person.java

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+package com.example.effectivejava.chapter01.item03.methodreference;
+
+import java.time.LocalDate;
+import java.util.ArrayList;
+import java.util.Comparator;
+import java.util.List;
+
+public class Person {
+
+    LocalDate birthday;
+
+    public Person() {
+
+    }
+
+    public Person(LocalDate birthday) {
+        this.birthday = birthday;
+    }
+
+    public static int compareByAge(Person a, Person b) {
+        return a.birthday.compareTo(b.birthday);
+    }
+
+    public int compareByAge2(Person a, Person b) {
+        return a.birthday.compareTo(b.birthday);
+    }
+
+    // 임의 객체 참조의 경우 첫번째 인자는 자기 자신
+    public int compareByAge3(Person b) {
+        return this.birthday.compareTo(b.birthday);
+    }
+
+
+    public static void main(String[] args) {
+        List<Person> people = new ArrayList<>();
+        people.add(new Person(LocalDate.of(1982, 7, 15)));
+        people.add(new Person(LocalDate.of(2011, 3, 2)));
+        people.add(new Person(LocalDate.of(2013, 1, 28)));
+
+        Person person = new Person(LocalDate.of(2022, 5, 14));
+
+        people.sort(Person::compareByAge);
+        people.sort(person::compareByAge2);
+        people.sort(Person::compareByAge3);
+    }
+
+    public int getAge() {
+        return LocalDate.now().getYear() - birthday.getYear();
+    }
+
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item03/serialization/Book.java

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+package com.example.effectivejava.chapter01.item03.serialization;
+
+import java.io.Serial;
+import java.io.Serializable;
+import java.time.LocalDate;
+
+public class Book implements Serializable {
+
+    @Serial
+    private static final long serialVersionUID = 1L;
+
+    private String isbn;
+
+    private String title;
+
+    private LocalDate published;
+
+    private String name;
+
+    private transient int numberOfSold;
+
+    public Book(String isbn, String title, String author, LocalDate published) {
+        this.isbn = isbn;
+        this.title = title;
+        this.published = published;
+    }
+
+    @Override
+    public String toString() {
+        return "Book{" +
+                "isbn='" + isbn + '\'' +
+                ", title='" + title + '\'' +
+                ", published=" + published +
+                ", numberOfSold=" + numberOfSold +
+                '}';
+    }
+
+    public String getIsbn() {
+        return isbn;
+    }
+
+    public void setIsbn(String isbn) {
+        this.isbn = isbn;
+    }
+
+    public String getTitle() {
+        return title;
+    }
+
+    public void setTitle(String title) {
+        this.title = title;
+    }
+
+    public LocalDate getPublished() {
+        return published;
+    }
+
+    public void setPublished(LocalDate published) {
+        this.published = published;
+    }
+
+    public int getNumberOfSold() {
+        return numberOfSold;
+    }
+
+    public void setNumberOfSold(int numberOfSold) {
+        this.numberOfSold = numberOfSold;
+    }
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item03/serialization/SerializationExample.java

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+package com.example.effectivejava.chapter01.item03.serialization;
+
+import java.io.*;
+import java.time.LocalDate;
+
+public class SerializationExample {
+
+    private void serialize(Book book) {
+        try (ObjectOutput out = new ObjectOutputStream(new FileOutputStream("book.obj"))) {
+            out.writeObject(book);
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    private Book deserialize() {
+        try (ObjectInput in = new ObjectInputStream(new FileInputStream("book.obj"))) {
+            return (Book) in.readObject();
+        } catch (IOException | ClassNotFoundException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    public static void main(String[] args) {
+        Book book = new Book("12345", "이팩티브 자바 완벽 공략", "백기선",
+                LocalDate.of(2022, 3, 21));
+        book.setNumberOfSold(200);
+
+        SerializationExample example = new SerializationExample();
+        example.serialize(book);
+        Book deserializedBook = example.deserialize();
+
+        System.out.println(book);
+        System.out.println(deserializedBook);
+    }
+}