What is the difference between inner class and nested class in Java?

What is the difference between inner class and nested class in Java?

I'd be happy to help!

In Java, an inner class (also known as a local class) and a nested class are two related but distinct concepts.

A nested class is a class that is defined inside another class or interface. This means that the outer class or interface defines the namespace for the nested class, which is also referred to as an anonymous class. A nested class does not have its own package statement; instead, it inherits the package of the enclosing class or interface.

Here's an example:

public class Outer {
public static class Inner {
// code here
}
}

In this example, Inner is a nested class within the Outer class. The Inner class has access to all members of the Outer class, including its methods and variables.

On the other hand, an inner class (or local class) is a special type of nested class that is defined inside a method. This means that the inner class has a closer relationship with the method it's defined within than with any other class in the program.

Here's an example:

public class Outer {
public void myMethod() {
class Inner {
// code here
}
}
}

In this example, Inner is an inner class that is defined inside the myMethod() method of the Outer class. The Inner class has access to all members of the enclosing method, including its local variables and parameters.

The key difference between a nested class and an inner class lies in their scope:

In summary, both nested classes and inner classes are forms of encapsulation in Java, but they differ in their scope and relationship with the enclosing class or interface. While a nested class is defined outside any particular method and has a broader scope, an inner class is defined inside a method and is scoped to that method alone.

Java inner class vs nested class javatpoint example

I'm glad you're interested in learning about the differences between Java inner classes and nested classes! Here's a detailed explanation, with examples from Javatpoint.

Java Inner Classes

In Java, an inner class is a class that is defined inside another class. The outer class (the one containing the inner class) has access to the inner class's private members. This means the outer class can create instances of the inner class and interact with them directly. Here's an example from Javatpoint:

class Outer {
int x = 10;
class Inner {
void display() {
System.out.println("Value of x is: " + x);
}
}
}
public class Main {
public static void main(String[] args) {
Outer outer = new Outer();
Outer.Inner inner = outer.new Inner();
inner.display(); // prints the value of x
}
}

In this example, Outer is the outer class, and Inner is an inner class. The main method creates an instance of the Outer class (outer) and then uses that instance to create an instance of the Inner class (inner). The display method in the Inner class has access to the private member x of the Outer class, which is why it can print its value.

Java Nested Classes

On the other hand, a nested class is a class that is defined inside another class, but unlike an inner class, a nested class does not have direct access to the outer class's members. A nested class is essentially a standalone class that happens to be defined within another class. Here's an example from Javatpoint:

class Outer {
int x = 10;
public static class Inner {
void display() {
System.out.println("Value of x is: " + x);
}
}
}
public class Main {
public static void main(String[] args) {
Outer.Inner inner = new Outer.Inner();
// error: cannot resolve symbol 'x'
// inner.display();  // compilation fails because Inner doesn't have access to x
}
}

In this example, Outer is the outer class, and Inner is a nested class. The main method creates an instance of the Inner class (inner) using the new Outer.Inner() syntax. However, since a nested class does not have direct access to its containing class's members, the display method in the Inner class cannot print the value of x.

Key Takeaways

I hope this explanation helps clarify the differences between Java inner classes and nested classes!