#10 effective java: item 8

effective-java/src/main/java/com/example/effectivejava/chapter01/item08/autocloseable/App.java

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+package com.example.effectivejava.chapter01.item08.autocloseable;
+
+public class App {
+
+    public static void main(String[] args) {
+        try(AutoClosableIsGood good = new AutoClosableIsGood("")) {
+            // TODO 자원 반납 처리가 됨.
+
+        }
+    }
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item08/autocloseable/AutoClosableIsGood.java

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+package com.example.effectivejava.chapter01.item08.autocloseable;
+
+import java.io.*;
+
+public class AutoClosableIsGood implements AutoCloseable {
+
+    private BufferedReader reader;
+
+    public AutoClosableIsGood(String path) {
+        try {
+            this.reader = new BufferedReader(new FileReader(path));
+        } catch (FileNotFoundException e) {
+            throw new IllegalArgumentException(path);
+        }
+    }
+
+    @Override
+    public void close() {
+        try {
+            reader.close();
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item08/cleaner/BigObject.java

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+package com.example.effectivejava.chapter01.item08.cleaner;
+
+import java.util.List;
+
+public class BigObject {
+
+    private List<Object> resource;
+
+    public BigObject(List<Object> resource) {
+        this.resource = resource;
+    }
+
+    public static class ResourceCleaner implements Runnable {
+
+        private List<Object> resourceToClean;
+
+        public ResourceCleaner(List<Object> resourceToClean) {
+            this.resourceToClean = resourceToClean;
+        }
+
+        @Override
+        public void run() {
+            resourceToClean = null;
+            System.out.println("cleaned up.");
+        }
+    }
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item08/cleaner/CleanerIsNotGood.java

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+package com.example.effectivejava.chapter01.item08.cleaner;
+
+import java.lang.ref.Cleaner;
+import java.util.ArrayList;
+import java.util.List;
+
+public class CleanerIsNotGood {
+
+    public static void main(String[] args) throws InterruptedException {
+        Cleaner cleaner = Cleaner.create();
+
+        List<Object> resourceToCleanUp = new ArrayList<>();
+        BigObject bigObject = new BigObject(resourceToCleanUp);
+        cleaner.register(bigObject, new BigObject.ResourceCleaner(resourceToCleanUp));
+
+        bigObject = null;
+        System.gc();
+        Thread.sleep(3000L);
+    }
+
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item08/cleaner_as_a_safeynet/Adult.java

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+package com.example.effectivejava.chapter01.item08.cleaner_as_a_safeynet;
+
+// cleaner 안전망을 갖춘 자원을 제대로 활용하는 클라이언트 (45쪽)
+public class Adult {
+    public static void main(String[] args) {
+        try (Room myRoom = new Room(7)) {
+            System.out.println("안녕~");
+        }
+    }
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item08/cleaner_as_a_safeynet/Room.java

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+package com.example.effectivejava.chapter01.item08.cleaner_as_a_safeynet;
+
+import java.lang.ref.Cleaner;
+
+// 코드 8-1 cleaner를 안전망으로 활용하는 AutoCloseable 클래스 (44쪽)
+public class Room implements AutoCloseable {
+    private static final Cleaner cleaner = Cleaner.create();
+
+    // 청소가 필요한 자원. 절대 Room을 참조해서는 안 된다!
+    private static class State implements Runnable {
+        int numJunkPiles; // Number of junk piles in this room
+
+        State(int numJunkPiles) {
+            this.numJunkPiles = numJunkPiles;
+        }
+
+        // close 메서드나 cleaner가 호출한다.
+        @Override public void run() {
+            System.out.println("Cleaning room");
+            numJunkPiles = 0;
+        }
+    }
+
+    // 방의 상태. cleanable과 공유한다.
+    private final State state;
+
+    // cleanable 객체. 수거 대상이 되면 방을 청소한다.
+    private final Cleaner.Cleanable cleanable;
+
+    public Room(int numJunkPiles) {
+        state = new State(numJunkPiles);
+        cleanable = cleaner.register(this, state);
+    }
+
+    @Override public void close() {
+        cleanable.clean();
+    }
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item08/cleaner_as_a_safeynet/Teenager.java

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+package com.example.effectivejava.chapter01.item08.cleaner_as_a_safeynet;
+
+// cleaner 안전망을 갖춘 자원을 제대로 활용하지 못하는 클라이언트 (45쪽)
+public class Teenager {
+
+    public static void main(String[] args) {
+        new Room(99);
+        System.out.println("Peace out");
+
+        // 다음 줄의 주석을 해제한 후 동작을 다시 확인해보자.
+        // 단, 가비지 컬렉러를 강제로 호출하는 이런 방식에 의존해서는 절대 안 된다!
+        System.gc();
+    }
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item08/finalizer/App.java

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+package com.example.effectivejava.chapter01.item08.finalizer;
+
+import java.lang.ref.ReferenceQueue;
+import java.lang.reflect.Field;
+
+public class App {
+
+    /**
+     * 코드 참고 https://www.baeldung.com/java-finalize
+     */
+    public static void main(String[] args) throws InterruptedException, ClassNotFoundException, NoSuchFieldException, IllegalAccessException {
+        int i = 0;
+        while (true) {
+            i++;
+            new FinalizerIsBad();
+
+            if ((i % 1_000_000) == 0) {
+                Class<?> finalizerClass = Class.forName("java.lang.ref.Finalizer");
+                Field queueStaticField = finalizerClass.getDeclaredField("queue");
+                queueStaticField.setAccessible(true);
+                ReferenceQueue<Object> referenceQueue = (ReferenceQueue) queueStaticField.get(null);
+
+                Field queueLengthField = ReferenceQueue.class.getDeclaredField("queueLength");
+                queueLengthField.setAccessible(true);
+                long queueLength = (long) queueLengthField.get(referenceQueue);
+                System.out.format("There are %d references in the queue%n", queueLength);
+            }
+        }
+    }
+}

effective-java/src/main/java/com/example/effectivejava/chapter01/item08/finalizer/FinalizerIsBad.java

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+package com.example.effectivejava.chapter01.item08.finalizer;
+
+public class FinalizerIsBad {
+
+    @Override
+    protected void finalize() throws Throwable {
+        System.out.print("");
+    }
+}