Core Java Basic Classes

😏 Core Java Classes Brief Introduction Topics :

#Abstract Class :
An Abstract Class is a class that is declared keyword abstract. it may  or may not include an abstract method

Abstract method:
A method that is a declared as abstract and does not have an implementation.

The abstract class can look something like this:

abstract class GraphicObject {
    int x, y;
    ...
    void moveTo(int newX, int newY) {
        ...
    }
    abstract void draw();
    abstract void resize();
}

#Interface class :
An interface class in java is a blueprint of a class, it has static constant and abstract method.there  can be the only abstract method in Java interface .(is-a relationship)

The Interface class can look something like this:

interface Bicycle {
    //  wheel revolutions per minute
    void changeCadence(int newValue);

    void changeGear(int newValue);

    void speedUp(int increment);

    void applyBrakes(int decrement);
}

#Marker Interface :
it is an empty interface (on field or method )

The Interface class can look something like this:

interface Bicycle {
//empty 
}

Cloneable Interface :
The Cloneable interface is present in java.lang.package. there is a method clone() in the object class
A class that implements the Cloneable interface indicates that itis legal for clone() method to make a field for field copy of an instance of that class.

Serializable Interface :

The Serializable interface is present in the 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.

Remote interface : 
The 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 the 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.

  

#Wrapper Class : 
A wrapper class is a class where object wraps or contains a primitive type.
when we create an object to wrapper class, it contains a field and infield, we can store a primitive datatype, in other words, we can wrap a primitive value into a wrapper class object.

Need od wrapper class :

• They convert primitive datatype into the object, object are needed if we wish to modify the arguments passed into a method.
• the classes in java.util package handle only object and hance wrapper classes help in the case also 
• A data structure in the collection framework, such as ArrayList and vector, store the only object and not the primitive type.
• An object is needed to support synchronized in multithreading 

Primitive Datatype and their corresponding wrapper class :

Autoboxing : 

Automatic conversion of primitive type to the object of their corresponding wrapper class is known as autoboxing. 

                          

Unboxing :

it is just the reverse process of autoboxing. automatically converting an object of wrapper class to it corresponding primitive type is known as unboxing.

#Casting  Class  :

Casting Really means in taking an object of one particular type and "turning it into" another object type. this process is called casting a variable.

Type Casting :

Assigning a value of one type to a variable of another type is known as typecasting.

Type Casting is classification into two type :

Widening casting (Implicit) :

• The target type is larger than the source type.
• it is automatic type conversion.
• JVM will create new object type.

Narrowing casting (Explicitly):
when you are assigning a larger type value to a variable of small type, the need to perform explicitly.

• Larger type value to the variable of small type value.
• the program will create new object typeset.

#Stream Class:

A stream can be defined as a sequence of data. hierarchy of classes for input and output streams. 

the input stream is used to read data from a source and the output stream is used for writing data to a destination. to perform read and write operation on binary files we need a mechanism to read that binary data on file / to write binary (i.e. in the form of byte)

#Generics Class :
We can define our own classes with generics type. A generic type is a class or interface that is parameterized over types. We use angle brackets (<>) to specify the type parameter.

class MyGen <T> {
 T obj;
 void add (T obj){ this.obj=obj; }
 T.get(){
  return obj;
 }
}

Generic method :

Like a generic class, we can create the generic method that can accept any type of argument.

public static<E> void printArray(E[] elements){
 
 for(E element:elements){
  System.out.println(element);
 }
}