Маркер интерфейс в Java
Это пустой интерфейс (без полей или методов). Примеры интерфейса маркера: Serializable, Clonnable и Remote interface. Все эти интерфейсы - пустые интерфейсы.
публичный интерфейс Serializable { // здесь ничего }
Examples of Marker Interface which are used in real-time applications :
- Cloneable interface : Cloneable interface is present in java.lang package. There is a method clone() in Object class. A class that implements the Cloneable interface indicates that it is legal for clone() method to make a field-for-field copy of instances of that class.
Invoking Object’s clone method on an instance of the class that does not implement the Cloneable interface results in an exception CloneNotSupportedException being thrown. By convention, classes that implement this interface should override Object.clone() method.
Refer here for more details.// Java program to illustrate Cloneable interface
import
java.lang.Cloneable;
// By implementing Cloneable interface
// we make sure that instances of class A
// can be cloned.
class
A
implements
Cloneable
{
int
i;
String s;
// A class constructor
public
A(
int
i,String s)
{
this
.i = i;
this
.s = s;
}
// Overriding clone() method
// by simply calling Object class
// clone() method.
@Override
protected
Object clone()
throws
CloneNotSupportedException
{
return
super
.clone();
}
}
public
class
Test
{
public
static
void
main(String[] args)
throws
CloneNotSupportedException
{
A a =
new
A(
20
,
"GeeksForGeeks"
);
// cloning "a" and holding
// new cloned object reference in b
// down-casting as clone() return type is Object
A b = (A)a.clone();
System.out.println(b.i);
System.out.println(b.s);
}
}
Output:
20 GeeksForGeeks
- Serializable interface : Serializable interface is present in java.io package. It is used to make an object eligible for saving its state into a file. This is called Serialization.
Classes that do not implement this interface will not have any of their state serialized or deserialized. All subtypes of a serializable class are themselves serializable.// Java program to illustrate Serializable interface
import
java.io.*;
// By implementing Serializable interface
// we make sure that state of instances of class A
// can be saved in a file.
class
A
implements
Serializable
{
int
i;
String s;
// A class constructor
public
A(
int
i,String s)
{
this
.i = i;
this
.s = s;
}
}
public
class
Test
{
public
static
void
main(String[] args)
throws
IOException, ClassNotFoundException
{
A a =
new
A(
20
,
"GeeksForGeeks"
);
// Serializing "a"
FileOutputStream fos =
new
FileOutputStream(
"xyz.txt"
);
ObjectOutputStream oos =
new
ObjectOutputStream(fos);
oos.writeObject(a);
// De-serializing "a"
FileInputStream fis =
new
FileInputStream(
"xyz.txt"
);
ObjectInputStream ois =
new
ObjectInputStream(fis);
A b = (A)ois.readObject();
//down-casting object
System.out.println(b.i+
" "
+b.s);
// closing streams
oos.close();
ois.close();
}
}
Output:
20 GeeksForGeeks
- Remote interface : Remote interface is present in java.rmi package. A remote object is an object which is stored at one machine and accessed from another machine. So, to make an object a remote object, we need to flag it with Remote interface. Here, Remote interface serves to identify interfaces whose methods may be invoked from a non-local virtual machine.Any object that is a remote object must directly or indirectly implement this interface. RMI (Remote Method Invocation) provides some convenience classes that remote object implementations can extend which facilitate remote object creation.
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