Add - Is there a Destructor in Java (#12345)

apeterlic · web-flow · commit 151e2981b874 · 2022-06-13T13:22:57.000-07:00
diff --git a/core-java-modules/core-java-9/src/main/java/com/baeldung/java9/finalizers/CleaningDemo.java b/core-java-modules/core-java-9/src/main/java/com/baeldung/java9/finalizers/CleaningDemo.java
@@ -0,0 +1,17 @@
+package com.bealdung.java9.finalizers;
+
+import java.lang.ref.Cleaner;
+
+class CleaningDemo {
+
+    public static void main(String[] args) {
+        final Cleaner cleaner = Cleaner.create();
+        try (Order order = new Order(cleaner)) {
+            for (int i = 0; i < 10; i++) {
+                order.register(new Product(i), i);
+            }
+        } catch (Exception e) {
+            System.err.println("Error: " + e);
+        }
+    }
+}
diff --git a/core-java-modules/core-java-9/src/main/java/com/baeldung/java9/finalizers/Order.java b/core-java-modules/core-java-9/src/main/java/com/baeldung/java9/finalizers/Order.java
@@ -0,0 +1,36 @@
+package com.bealdung.java9.finalizers;
+
+import java.lang.ref.Cleaner;
+
+class Order implements AutoCloseable {
+
+    private final Cleaner cleaner;
+    private Cleaner.Cleanable cleanable;
+
+    public Order(Cleaner cleaner) {
+        this.cleaner = cleaner;
+    }
+
+    public void register(Product product, int id) {
+        this.cleanable = cleaner.register(product, new CleaningAction(id));
+    }
+
+    public void close() {
+        cleanable.clean();
+        System.out.println("Cleanable closed");
+    }
+
+    static class CleaningAction implements Runnable {
+
+        private final int id;
+
+        public CleaningAction(int id) {
+            this.id = id;
+        }
+
+        @Override
+        public void run() {
+            System.out.printf("Object with id %s is garbage collected. %n", id);
+        }
+    }
+}
diff --git a/core-java-modules/core-java-9/src/main/java/com/baeldung/java9/finalizers/Product.java b/core-java-modules/core-java-9/src/main/java/com/baeldung/java9/finalizers/Product.java
@@ -0,0 +1,13 @@
+package com.bealdung.java9.finalizers;
+
+class Product {
+    private final int id;
+
+    public Product(int id) {
+        this.id = id;
+    }
+
+    public int getId() {
+        return id;
+    }
+}
diff --git a/core-java-modules/core-java-9/src/main/java/com/baeldung/java9/finalizers/Resource.java b/core-java-modules/core-java-9/src/main/java/com/baeldung/java9/finalizers/Resource.java
@@ -0,0 +1,25 @@
+package com.bealdung.java9.finalizers;
+
+import java.io.BufferedReader;
+import java.io.FileNotFoundException;
+import java.io.FileReader;
+
+class Resource implements AutoCloseable {
+
+    final BufferedReader reader;
+
+    public Resource(String filename) throws FileNotFoundException {
+        reader = new BufferedReader(new FileReader(filename));
+    }
+
+    public long getLineNumber() {
+        return reader.lines()
+            .count();
+    }
+
+    @Override
+    public void close() throws Exception {
+        reader.close();
+        System.out.println("BufferedReader resource closed");
+    }
+}
diff --git a/core-java-modules/core-java-9/src/test/java/com/baeldung/java9/finalizers/FinalizeUnitTest.java b/core-java-modules/core-java-9/src/test/java/com/baeldung/java9/finalizers/FinalizeUnitTest.java
@@ -0,0 +1,30 @@
+package com.bealdung.java9.finalizers;
+
+import org.junit.jupiter.api.Test;
+
+import java.io.BufferedWriter;
+import java.io.File;
+import java.io.FileWriter;
+import java.io.IOException;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class FinalizeUnitTest {
+
+    @Test
+    void givenFilename_whenGetLineNumber_thenReturnCorrectNumber() throws IOException {
+        final File tmpFile = File.createTempFile("test", ".tmp");
+        final BufferedWriter writer = new BufferedWriter(new FileWriter(tmpFile));
+        writer.write("Baeldung");
+        writer.close();
+
+        long lineNumber = 0;
+        try (Resource resource = new Resource(tmpFile.getAbsolutePath())) {
+            lineNumber = resource.getLineNumber();
+        } catch (Exception e) {
+            System.err.println("Error " + e);
+        }
+
+        assertEquals(1, lineNumber);
+    }
+}
