4. Java OOP. 6. Inner Classes презентация

4. Java OOP 6. Inner Classes

Nested Classes (1 of 2) A nested class is a class defined within another class: class OuterClass { ... class NestedClass { ... } }

Nested Classes (2 of 2) A nested class is a member of its enclosing class Non-static nested classes (inner classes) have access to other members of the enclosing class, even if they are declared private Static nested classes do not have access to other instance members of the enclosing class

Why Use Nested Classes? It is a way of logically grouping classes that are only used in one place. It increases encapsulation. Nested classes can lead to more readable and maintainable code (places the code closer to where it is used)

Static Nested Classes (1 of 2) A static nested class is associated with its outer class Like static class methods, a static nested class cannot refer directly to instance variables or methods defined in its enclosing class - it can use them only through an object reference

Static Nested Classes (2 of 2) Static nested classes are accessed using the enclosing class name: OuterClass.StaticNestedClass To create an object for the static nested class, use this syntax: OuterClass.StaticNestedClass nestedObject = new OuterClass.StaticNestedClass();

Inner Classes (1 of 2) An inner class has direct access to that object's methods and fields It cannot define any static members itself Objects that are instances of an inner class exist within an instance of the outer class

Inner Classes (2 of 2) To instantiate an inner class, you must first instantiate the outer class. Then, create the inner object within the outer object with this syntax: outerClass.InnerClass innerObject = outerObject.new InnerClass();

Local Inner Classes Inner classes can be created inside code blocks, typically inside the body of a method A local inner class cannot have an access specifier It does have access to the final variables in the current code block and all the members of the enclosing class

Anonymous Classes Anonymous classes combine the process of definition and instantiation into a single step As these classes do not have a name, an instance of the class can only be created together with the definition

Anonymous Class Example I new Thread(new Runnable() { public void run() { ... } }).start();

Anonymous Class Example II JFrame frame = new JFrame("AnonimDemo2"); frame.addWindowListener(new WindowAdapter() { public void windowClosing(WindowEvent e) { System.exit(0); } });

Anonymous Classes Use For creating objects on the fly in contexts such as: the value in a return statement an argument in a method call in initialization of variables to implement event listeners in GUI-based applications

Manuals http://docs.oracle.com/javase/tutorial/java/javaOO/nested.html