In Java, just like methods, variables of a class too can have another class as its member. Writing a class within another is allowed in Java. The class written within is called the nested class, and the class that holds the inner class is called the outer class.
Syntax
The syntax to write a nested class is given below. Here the class Outer_Demo is the outer class and the class Inner_Demo is the nested class.
class Outer_Demo{
class Nested_Demo{
}
}
Nested classes are divided into two types:
Non-static nested classes: These are the non-static members of a class.
Static nested classes: These are the static members of a class
Inner Classes (Non-static Nested Classes)
Inner classes are a security mechanism in Java. We know a class cannot be associated with the access modifier private, but if we have the class as a member of other class, then the inner class can be made private. And this is also used to access the private members of a class.
Inner classes are of three types depending on how and where you define them. They are:
Inner Class
Method-local Inner Classlass
Anonymous Inner Class
Inner Class
Creating an inner class is quite simple. You just need to write a class within a class. Unlike a class, an inner class can be private and once you declare an inner class private, it cannot be accessed from an object outside the class.
Given below is the program to create an inner class and access it. In the given example, we make the inner class private and access the class through a method.
class Outer_Demo{
int num;
//inner class
private class Inner_Demo{
public void print(){
System.out.println("This is an inner class");
}
}
//Accessing he inner class from the method within
void display_Inner(){
Inner_Demo inner = new Inner_Demo();
inner.print();
}
}
public class My_class{
public static void main(String args[]){
//Instantiating the outer class
Outer_Demo outer = new Outer_Demo();
//Accessing the display_Inner() method.
outer.display_Inner();
}
}
Here you can observe that Outer_Demo is the outer class, Inner_Demo is the inner class, display_Inner() is the method inside which we are instantiating the inner class, and this method is invoked from the main method.
If you compile and execute the above program, you will get the following result.
This is an inner class.
public class StringDemo{
public static void main(String args[]){
char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.'};
String helloString = new String(helloArray);
System.out.println( helloString );
}
}
This would produce the following result:
hello.
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