Inner classes in java

Java Inner Classes
-Arulkumar V
Assistant Professor, SECE

Interface in Java
 Java inner class or nested class is a class
which is declared inside the class or
interface.
 We use inner classes to logically group
classes and interfaces in one place so that
it can be more readable and maintainable.
 Additionally, it can access all the members
of outer class including private data
members and methods.

Syntax of Inner class
class Java_Outer_class{
//code
class Java_Inner_class{
//code
}
}

Advantage of java inner classes
There are basically three advantages of inner classes in java. They
are as follows:
1) Nested classes represent a special type of relationship that is it
can access all the members (data members and methods) of
outer class including private.
2) Nested classes are used to develop more readable and
maintainable code because it logically group classes and
interfaces in one place only.
3) Code Optimization: It requires less code to write.

Types of Nested classes
There are two types of nested classes
non-static and static nested classes.
The non-static nested classes are also known as
inner classes.
>Non-static nested class (inner class)
Member inner class
Anonymous inner class
Local inner class
>Static nested class

Java Member inner class In this example, we are creating msg()
method in member inner class that is accessing the private data
member of outer class.
class TestMemberOuter1{
private int data=30;
class Inner{
void msg(){System.out.println("data is "+data);}
}
public static void main(String args[]){
TestMemberOuter1 obj=new TestMemberOuter1();
TestMemberOuter1.Inner in=obj.new Inner();
in.msg();
}
}

Java anonymous inner class example using class
abstract class Person{
abstract void eat();
}
class TestAnonymousInner{
Person p=new Person(){
void eat(){System.out.println("nice fruits");}
};
p.eat();
}
}

Java local inner class example
public class localInner1{
private int data=30;//instance variable
void display(){
class Local{
void msg(){System.out.println(data);}
}
Local l=new Local();
l.msg();
}
localInner1 obj=new localInner1();
obj.display();
}
}

Java static nested class
 A static class i.e. created inside a class is called static
nested class in java. It cannot access non-static data
members and methods. It can be accessed by outer
class name.
◦ It can access static data members of outer class including
private.
◦ Static nested class cannot access non-static (instance) data
member or method.

Java static nested class example with
instance method
class TestOuter1{
static int data=30;
static class Inner{
void msg(){System.out.println("data is "+data);}
}
TestOuter1.Inner obj=new TestOuter1.Inner();
obj.msg();
}
}

Thank You
19-12-2017 Sampath Kumar.S, AP/IT 12

Inner classes in java

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