What is an Externalizable interface?

Externalization serves the purpose of custom Serialization, where we can decide what to store in stream. Externalizable interface present in java.io, is used for Externalization which extends Serializable interface. It consist of two methods which we have to override to write/read object into/from stream which are-

Which is the best case to use the Externalizable interface in java?

We can achieve custom serialization with the Serializable interface by marking the field with transient keyword. The JVM won’t serialize the particular field but it’ll add up the field to file storage with the default value. That’s why it’s a good practice to use Externalizable in case of custom serialization.

How does serialization takes place in java What is purpose of Externalizable interface What are transient variables?

The Externalizable interface provides control over the serialization process. Because the transient keyword designates a field not to be persisted, we can use it on any field that we do not want to be serialized.

Is Externalizable a marker interface?

The externalizable interface is not a marker interface and thus it defines two methods writeExternal() and readExternal(). Serialization using an externalizable interface has better performance. Default serialization does not require any no-arg constructor.

What is cloneable interface?

Cloneable interface is a marker interface. It was introduced in JDK 1.0. There is a method clone() in the Object class. Cloneable interface is implemented by a class to make Object. clone() method valid thereby making field-for-field copy.

How an object can become serializable?

How an object can become serializable? Explanation: A Java object is serializable if class or any its superclass implements java. io. Explanation: Deserialization is the reverse process of serialization which is turning stream of bytes into an object in memory.

What will happen if we don’t implement Serializable?

What happens if you try to send non-serialized Object over network? When traversing a graph, an object may be encountered that does not support the Serializable interface. In this case the NotSerializableException will be thrown and will identify the class of the non-serializable object.

Why Serializable is a marker interface?

That Serializable is a marker interface means that it contains no methods. Therefore, a class implementing Serializable does not have to implement any specific methods. Implementing Serializable thus just tells the Java serialization classes that this class is intended for object serialization.

Is cloneable a marker interface?

The Serializable and Cloneable interfaces are the example of marker interface. In short, it indicates a signal or command to the JVM. The declaration of marker interface is the same as interface in Java but the interface must be empty.

Why is cloneable bad?

What are disadvantages of Cloneable? Cloning is very dangerous if the object whom you are copying has composition. You need to think about below possible side effect in this case because clone creates shallow copy: Let say you have one object to handle db related manipulation.

Which is better serialization interface or externalizable interface?

Serializable interface has less control over serialization process and it is optional to override readObject and writeObject. Externalizable interface has more control over serialization process and it is mandatory to override writeExternal and readExternal.

Where does the externalizable interface in Java come from?

Externalizable extends from the java.io.Serializable marker interface. Any class that implements Externalizable interface should override the writeExternal (), readExternal () methods. That way we can change the JVM’s default serialization behavior.

When to use writeexternal method in externalizable interface?

So, when we write “Car” object to OutputStream, writeExternal method is called to persist the data. The same applies to the readExternal method. When an Externalizable object is reconstructed, an instance is created first using the public no-argument constructor, then the readExternal method is called.

When does a JVM inherit from a Serializable interface?

When a class inherits from the Serializable interface, the JVM automatically collects all the fields from sub-classes as well and makes them serializable. Keep in mind that we can apply this to Externalizable as well. We just need to implement the read/write methods for every sub-class of the inheritance hierarchy.