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POService Loader implementations needing default public constructors
 

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    <p>I was trying to understand how in Java Service Loader works? I came across this <a href="http://technotes.tostaky.biz/2013/03/java-serviceloader-example.html" rel="nofollow">blog</a>:</p> <p>Could you please help me understand why the author claims:</p> <blockquote> <p>The implementation must have a public parameterless constructor.</p> </blockquote> <p>Okay I get the first part. Now a follow up question. I can post it as a follow up a question but thought it would be better to have it as part of the same question. </p> <p>Consider the <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-13.html#jls-13.1-110-F.2" rel="nofollow">java doc</a>:</p> <p>It says:</p> <blockquote> <p>In addition, the constructor of a non-private inner member class must be compiled such that it has as its first parameter, an additional implicit parameter representing the immediately enclosing instance (§8.1.3). </p> </blockquote> <p>So does that mean I cannot externalize a inner class. Please consider the following code:</p> <pre><code>import java.io.*; class Y { class ABC { ABC() { System.out.println("ABC Constructor"); } public void writeExternal(ObjectOutput out) throws IOException { System.out.println("ABC.writeExternal"); } public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException { System.out.println("ABC.readExternal"); } } public void foo() throws IOException, ClassNotFoundException { System.out.println("Constructing objects:"); ABC abc = new ABC(); ObjectOutputStream o = new ObjectOutputStream( new FileOutputStream("InnerClass.out")); System.out.println("Saving objects:"); o.writeObject(abc); o.close(); // Now get them back: ObjectInputStream in = new ObjectInputStream( new FileInputStream("InnerClass.out")); System.out.println("Recovering abc:"); // OOPS! Throws an exception: abc = (ABC)in.readObject(); } } public class InnerClass { public static void main(String[] args) throws IOException, ClassNotFoundException { System.out.println("Hello World\n"); Y y = new Y(); System.out.println(y); y.foo(); } } </code></pre> <p>It fails at runtime:</p> <pre><code>Hello World Y@6bc7c054 Constructing objects: ABC Constructor Saving objects: Exception in thread "main" java.io.NotSerializableException: Y$ABC at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1180) at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:346) at Y.foo(InnerClass.java:24) at InnerClass.main(InnerClass.java:40) </code></pre> <p>How can I use Externalize class ABC? </p> <p>Thanks</p>
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