Java - Packages & Interface
EXPLAIN : PACKAGE
- Package is java's way of grouping the classes, interfaces & sub packages together.
- It can also be known as a container for classes & interfaces.
- Package in Java can be categorized in two form, Built-in package & User-defined package.
- The Java library provides a large number of classes grouped into different packages according to the functionality.
- For example, While using "println()" method, We have to use the "java.lang.*;" default package.
IMPORTANCE : PACKAGE
- By using packages, Programmers can define their own packages to bundle a group of classes / interfaces and etc.
- Programmers can determine the Classes, Interfaces, Enumeration & Annotations easily by using the feature "Packages"
EXPLAIN : PACKAGES IN JAVA
- java.lang : "Language" supports classes such as the System, Thread, Exception and etc.
- java.util : "Utility" supports classes such as Vector, Array, Linked List, Stack and etc.
- java.io : "Input output" supports classes such as BufferedReader, InputStream.
- java.awt : It supports the Classes which includes GUI such as Window, Frame, Panel & etc.
- java.applet : It is used for creating & implementing the Applets in java.
EXPLAIN : HOW TO CREATE A PACKAGE
- Declare a package at the beginning of the gile using following syntax:
- package packagename;
- Define a class that is to be put in the package and declare it in the public.
- Create the sub directory with the same name as the package name.
- Store the ".java" file in that sub directory.
- Compile the ".java" file, So that it creates the ".class" file in the sub directory.
SYNTAX : PACKAGE
package myPackage;
public class MyClass
{
// Body Of The Class
}
EXAMPLE : PACKAGE
package p1;
public class Abc
{
void show()
{
System.out.println("This Is The package 'p1' Which Contains The Class 'Abc'");
}
}
EXPLAIN : HOW TO ACCESS THE JAVA PACKAGE
- There are 3 ways of accessing a Java package
- Importing the package.*;
- Import package.classname;
- By fully qualified name
LIST : WAYS TO ACCESS PACKAGES IN JAVA
- Importing the "package.*;"
- Importing the "package.classname;"
- Fully qualified name
EXPLAIN : WAYS TO ACCESS PACKAGES IN JAVA
- Importing the "package.*;"
- If you use "package.*;", Then all the classes and interfaces are available to the package and it will be accesible to the class.
- The IMPORT keyword is sued to make the classes of another package accessible to the another classes.
- Importing the "package.classname;"
- If you import the "package.classname;", Then only declared class of this package is accesible.
- Fully qualified name
- If you use a fully qualified name, Then only the declared class of this package is accessible.
- In this, There is no need to implement the IMPORT statement, But you need to use the fully qualified name to access the class.
EXPLAIN : HOW TO ADD A "CLASS" TO THE PACKAGE
- It is simple to add a class to an existing package consider the following package:
package p1;
public class A
{
// Body Of "A"
}
- The package contains one public class by the name "A". Another class can be added by doing as follows:
- Define the class & make it public:
package p1;
public class B
{
// Body of "B"
}
- Store this as "B.java" file under the directory "p1".
- Compile "B.java". Thus, it will create a "B.class" file
- Place the class file in the directory "p1".
- Now the package "p1" contaims both the classes "A" & "B".
- Use the statement "import p1.*;". Thus, It will import both of the classes "A" & "B"
EXPLAIN : WHAT ARE ACCESS SPECIFIERS IN JAVA
- Java provides a number of access modifiers to set access leveels for the classes and it's variables, methods & constructors.
LIST & DEFINE : ACCESS SPECIFIERS IN JAVA
- Private : It is visible to the class only.
- Public : It is visible to the world.
- Protected : It is visible to the Packages & All the Subclasses
- Default : It is visible to the package, If no access specifier is used. Then a default specifier is used.
EXPLAIN : MULTIPLE INHERITANCE IN JAVA
- A class which is derived with several base classes is known as multiple inheritance. A class can inherit the attributes of two or more classes.
- To reduce the complexity, Multiple inheritance is not supported in Java. And thus, Interface is used to achieve Multiple Inheritance.
- The Classes in Java cannot have more than pne super class.
EXAMPLE : MULTIPLE INHERITANCE IN JAVA
import java.lang.*;
class A
{
void msg()
{
System.out.println("Hello!");
}
}
class B
{
void msg()
{
System.out.println("Welcome!");
}
}
class C extends A, B
{
public static void main (String args[])
{
C obj = new C();
obj.Msg();
}
}
EXPLAIN : INTERFACE
- Interface is mainly used for achieving Multiple Inheritance in Java.
- Interface is simple a blueprint of class.
- Once a interface is defined, Any number of classes can implement an interface.
FEATURES : INTERFACE
- Interface cannot be instantiated like the abstract class.
- Interfaces are similar to classes, But they do not have instance variables and their methods are declared without having any body.
- Interface contains abstract methods & final, static type of variables.
- Variables cannot be declared in private & protected modifiers.
- And, Methods cannot be declared in final, static, synchronized & native.
IMPORTANCE : INTERFACE
- Interface is used to reduce the complexity of the Java language. Thus, To achieve Multiple Inheritance, The concept of Inheritance is used.
SYNTAX : INTERFACE
acessspecifier interface interfacename
{
final static datatype varname1 = value;
final static datatype varname2 = value;
...
final static datatype varnamen = value;
returntype methodname1(parameters);
returntype methodname2(parameters);
...
returntype methodnamen(parameters);
}
EXPLAIN : HOW TO IMPLEMENT INTERFACE
- Once an Interface has been defined, One or more Classes can be implemented in that Interface.
- To implement an interface, We have to include the implement clause in a class definition.
EXAMPLE : INTERFACE
public interface Sport
{
final static int sport_marks = 100;
void calculate();
void show();
}
EXPLAIN : EXTENDING THE INTERFACE
- Class EXTENDS another class, An Interface EXTENDS another Interface. But a Class IMPLEMENTS an Interface.
EXAMPLE : EXTENDING THE INTERFACE
interface A
{
final static int num = 100;
void show();
}
interface B extends A
{
void display();
}
COMPARE : CLASS V/S INTERFACE
- Class are extended by another Class. / Interface are implemented by another Class.
- Methods of Class can be called using the object of the Class. / Method of Interface should be defined in the Class which implements the Interface.
- Variable of Class can be final or not. / Variable of Interface is always final.
- Class can extend only one Class. / Class can implement more than one Interface.
- A Class can define Constructors. / A Interface does not have a Constructor.
- Class can be in public, private or protected specifiers. / Interface is only in the public specifier.
- Objects of the Class can be created. / Object of an Interface cannot be created.
PROGRAMS!
- Package is java's way of grouping the classes, interfaces & sub packages together.
- It can also be known as a container for classes & interfaces.
- Package in Java can be categorized in two form, Built-in package & User-defined package.
- The Java library provides a large number of classes grouped into different packages according to the functionality.
- For example, While using "println()" method, We have to use the "java.lang.*;" default package.
IMPORTANCE : PACKAGE
- By using packages, Programmers can define their own packages to bundle a group of classes / interfaces and etc.
- Programmers can determine the Classes, Interfaces, Enumeration & Annotations easily by using the feature "Packages"
EXPLAIN : PACKAGES IN JAVA
- java.lang : "Language" supports classes such as the System, Thread, Exception and etc.
- java.util : "Utility" supports classes such as Vector, Array, Linked List, Stack and etc.
- java.io : "Input output" supports classes such as BufferedReader, InputStream.
- java.awt : It supports the Classes which includes GUI such as Window, Frame, Panel & etc.
- java.applet : It is used for creating & implementing the Applets in java.
EXPLAIN : HOW TO CREATE A PACKAGE
- Declare a package at the beginning of the gile using following syntax:
- package packagename;
- Define a class that is to be put in the package and declare it in the public.
- Create the sub directory with the same name as the package name.
- Store the ".java" file in that sub directory.
- Compile the ".java" file, So that it creates the ".class" file in the sub directory.
SYNTAX : PACKAGE
package myPackage;
public class MyClass
{
// Body Of The Class
}
EXAMPLE : PACKAGE
package p1;
public class Abc
{
void show()
{
System.out.println("This Is The package 'p1' Which Contains The Class 'Abc'");
}
}
EXPLAIN : HOW TO ACCESS THE JAVA PACKAGE
- There are 3 ways of accessing a Java package
- Importing the package.*;
- Import package.classname;
- By fully qualified name
LIST : WAYS TO ACCESS PACKAGES IN JAVA
- Importing the "package.*;"
- Importing the "package.classname;"
- Fully qualified name
EXPLAIN : WAYS TO ACCESS PACKAGES IN JAVA
- Importing the "package.*;"
- If you use "package.*;", Then all the classes and interfaces are available to the package and it will be accesible to the class.
- The IMPORT keyword is sued to make the classes of another package accessible to the another classes.
- Importing the "package.classname;"
- If you import the "package.classname;", Then only declared class of this package is accesible.
- Fully qualified name
- If you use a fully qualified name, Then only the declared class of this package is accessible.
- In this, There is no need to implement the IMPORT statement, But you need to use the fully qualified name to access the class.
EXPLAIN : HOW TO ADD A "CLASS" TO THE PACKAGE
- It is simple to add a class to an existing package consider the following package:
package p1;
public class A
{
// Body Of "A"
}
- The package contains one public class by the name "A". Another class can be added by doing as follows:
- Define the class & make it public:
package p1;
public class B
{
// Body of "B"
}
- Store this as "B.java" file under the directory "p1".
- Compile "B.java". Thus, it will create a "B.class" file
- Place the class file in the directory "p1".
- Now the package "p1" contaims both the classes "A" & "B".
- Use the statement "import p1.*;". Thus, It will import both of the classes "A" & "B"
EXPLAIN : WHAT ARE ACCESS SPECIFIERS IN JAVA
- Java provides a number of access modifiers to set access leveels for the classes and it's variables, methods & constructors.
LIST & DEFINE : ACCESS SPECIFIERS IN JAVA
- Private : It is visible to the class only.
- Public : It is visible to the world.
- Protected : It is visible to the Packages & All the Subclasses
- Default : It is visible to the package, If no access specifier is used. Then a default specifier is used.
EXPLAIN : MULTIPLE INHERITANCE IN JAVA
- A class which is derived with several base classes is known as multiple inheritance. A class can inherit the attributes of two or more classes.
- To reduce the complexity, Multiple inheritance is not supported in Java. And thus, Interface is used to achieve Multiple Inheritance.
- The Classes in Java cannot have more than pne super class.
EXAMPLE : MULTIPLE INHERITANCE IN JAVA
import java.lang.*;
class A
{
void msg()
{
System.out.println("Hello!");
}
}
class B
{
void msg()
{
System.out.println("Welcome!");
}
}
class C extends A, B
{
public static void main (String args[])
{
C obj = new C();
obj.Msg();
}
}
EXPLAIN : INTERFACE
- Interface is mainly used for achieving Multiple Inheritance in Java.
- Interface is simple a blueprint of class.
- Once a interface is defined, Any number of classes can implement an interface.
FEATURES : INTERFACE
- Interface cannot be instantiated like the abstract class.
- Interfaces are similar to classes, But they do not have instance variables and their methods are declared without having any body.
- Interface contains abstract methods & final, static type of variables.
- Variables cannot be declared in private & protected modifiers.
- And, Methods cannot be declared in final, static, synchronized & native.
IMPORTANCE : INTERFACE
- Interface is used to reduce the complexity of the Java language. Thus, To achieve Multiple Inheritance, The concept of Inheritance is used.
SYNTAX : INTERFACE
acessspecifier interface interfacename
{
final static datatype varname1 = value;
final static datatype varname2 = value;
...
final static datatype varnamen = value;
returntype methodname1(parameters);
returntype methodname2(parameters);
...
returntype methodnamen(parameters);
}
EXPLAIN : HOW TO IMPLEMENT INTERFACE
- Once an Interface has been defined, One or more Classes can be implemented in that Interface.
- To implement an interface, We have to include the implement clause in a class definition.
EXAMPLE : INTERFACE
public interface Sport
{
final static int sport_marks = 100;
void calculate();
void show();
}
EXPLAIN : EXTENDING THE INTERFACE
- Class EXTENDS another class, An Interface EXTENDS another Interface. But a Class IMPLEMENTS an Interface.
EXAMPLE : EXTENDING THE INTERFACE
interface A
{
final static int num = 100;
void show();
}
interface B extends A
{
void display();
}
COMPARE : CLASS V/S INTERFACE
- Class are extended by another Class. / Interface are implemented by another Class.
- Methods of Class can be called using the object of the Class. / Method of Interface should be defined in the Class which implements the Interface.
- Variable of Class can be final or not. / Variable of Interface is always final.
- Class can extend only one Class. / Class can implement more than one Interface.
- A Class can define Constructors. / A Interface does not have a Constructor.
- Class can be in public, private or protected specifiers. / Interface is only in the public specifier.
- Objects of the Class can be created. / Object of an Interface cannot be created.
PROGRAMS!