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In our previous article we have explained a simple version of an inner class, in which we have defined a class inside another class. Now let us see a little complicated version of an inner class, which is defining a class inside a method of another class. Yes, you've read it right.

We can even define a class inside a method of another class. That's why such version of an inner class is called a method-local inner class.

Important point about method-local inner class:

• A method-local inner class can access the variables of a class in which is defined.
• A method-local inner class can access the variables of a method in which it is defined(JDK 1.8 only). More on this in the coding examples below.
• A local variable declared in a method cannot be marked as private, public, protected or static. In a similar way, a method-local inner class cannot be marked as private, public, protected or static, because it gets similar privileges as a local variable defined in a method.

A simple method-local inner class

Having a method-local inner class imposes a lot of restrictions on how we can instantate its object as compared to instantiating an object of a regular inner class. Let's see this by an example -:

//Java - Example of method local inner class

class OuterC
{
public void  outerMethod()
{
	class InnerC //Inner class cannot have a public/private modifier as it's local to a method
	{
		public void innerMethod() //but it's method can have any modifier because it's declared inside a class.
		{
			System.out.println("Inner method");
		}
	}
	System.out.println("Outer method");
}


public static void main(String... ar)
{
	OuterC ob= new OuterC();
	ob.outerMethod();
}

}

Output is :

Outer method

Program Analysis

• Here, we have defined a method-local inner class, InnerC, inside a method of an outer class, OuterC.
• In the main() method, we have created an object(ob) of the outer class, OuterC.
• The method outerMethod() is invoked and within it we have defined our method-local inner class, InnerC.
• As we have not created an object of this inner class, InnerC, hence we couldn't call its method, innerMethod(), but the System.out.println() statement outside the body of InnerC is executed and the message Outer method is displayed.

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Instantiating an object of a method-local inner class and calling its method

The only way to create an object of a method-local inner class is right after the place where its definition ends in the method. Let's understand this by an example.

//Java - Example of method local inner class
 
public class OuterC
{
int b=20;

public void outerMethod()
{
int a=10;
	
	//method-local innner class
	class InnerC 		
	{
		public void innerMethod()
		{
			System.out.println("Inner Method");
			System.out.println("Accessing outerMethod() member variable, a = " + a);
			System.out.println("Accessing outer class member variable, b = " + b);
		}
	}
	InnerC ob = new InnerC();  //method-local inner class can only be instantiated right after its definition ends in the method.
	ob.innerMethod();	   //calling inner class's method
}

public static void main(String... ar)
{
	OuterC ob= new OuterC();
	ob.outerMethod();
}

}

Output is - :

Inner Method
Accessing outerMethod() member variable, a = 10
Accessing outer class member variable, b = 20

Program Analysis

• Here, we have defined a method-local inner class, InnerC, inside a method of an outer class, OuterC.
• In the main() method, we have created an object(ob) of the outer class, OuterC.
• The method outerMethod() is invoked and within it we have defined our method-local inner class, InnerC.
• At the end of the definition of our method-local inner class, InnerC>, we have created its object and have called its method, innerMethod().
• Within the method, innerMethod(), we have accessed a member variable(a) of the outer class, OuterC, and we have also accessed a member variable(b) of the method, outerMethod()

Accessing a method's member variable from within method-local inner class is a feature of JDK 1.8 only, prior to that version of JDK, it gives an error.

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