java-topology/test/langtools/tools/javac/warnings/Serial/Extern.java

/*
 * @test /nodynamiccopyright/
 * @bug 8202056
 * @compile/ref=Extern.out -XDrawDiagnostics -Xlint:serial Extern.java
 * @compile/ref=empty.out  -XDrawDiagnostics               Extern.java
 */

import java.io.*;

class Extern implements Externalizable {
    private static final long serialVersionUID = 42;

    // No-arg constructor on an Externalizable class must be public
    protected Extern() {}

    // ineffectual
    private static final ObjectStreamField[] serialPersistentFields = {};

    public void writeExternal(ObjectOutput out) throws IOException {
        return;
    }

    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
        return;
    }

    // ineffectual
    private void readObject(ObjectInputStream stream)
        throws IOException, ClassNotFoundException {
        stream.defaultReadObject();
    }

    // ineffectual
    private void writeObject(ObjectOutputStream stream) throws IOException {
        stream.defaultWriteObject();
    }

    // ineffectual
    private void readObjectNoData() throws ObjectStreamException {
        return;
    }

    // (possibly) effective
    private Object writeReplace() throws ObjectStreamException {
        return null;
    }

    // (possibly) effective
    private Object readResolve() throws ObjectStreamException {
        return null;
    }
}