Ch 10 Object-Oriented Programming: Polymorphism and Interfaces

differences of abstract and concrete classes

- Abstract superclasses are too general to create real objects, they specify only what is common among subclasses. - Concrete classes provide the specifics that make it reasonable to instantiate objects

three ways to assign superclass ans subclass references

- Assigning a superclass reference to a superclass variable - Assigning a subclass reference to a subclass variable - Assigning a subclass reference to a superclass variable

concrete classes

- Classes that can be used to instantiate objects - Such classes provide implementations of every method they declare (some of the implementations can be inherited).

common interface of the Java API

- Comparable - serialization - Runnable - GUI event-listener interfaces - AutoCloseable

Polymorphism

- Enables you to "program in the general" rather than "program in the specific." - enables you to write programs that process objects that share the same superclass as if they were all objects of the superclass; this can simplify programming.

extensible design and systems

- New classes can be added with little or no modification to the general portions of the program, as long as the new classes are part of the inheritance hierarchy that the program processes generically

Abstract classes

- Sometimes it's useful to declare classes for which you never intend to create objects. - Cannot be used to instantiate objects, they are incomplete - provides a superclass from which other classes can inherit and thus share a common design

final method

- a superclass cannot be overridden in a subclass.

Interfaces

- are particularly useful for assigning common functionality to possibly unrelated classes - Allows objects of unrelated classes to be processed polymorphically, objects of classes that implement the same interface can respond to all of the interface method calls

static binding

- calls to final methods are resolved at compile time - declaration can never change, so all subclasses use the same method implementation

variable

- can be used to invoke only those methods that are members of that variable's type, which the compiler verifies.

final class

- cannot be extended to create a subclass - class where all methods are implicitly final

declaring a method in an interface

- choose a method name that describes the method's purpose in a general manner, because the method may be implemented by many unrelated classes

Comparable

- common interface of java API used to allow objects of a class that implements the interference to be compared to one another - commonly used for ordering objects in a collection such as an array

Runnable

- common interfaces of the Java API - Implemented by any class that represents a task to perform - Contains one method, run, with specifies the behavior of an object when executed

AutoCloseable

- common interfaces of the java API - Implemented by classes that can be used with the try-with-resources statement to help prevent resource leaks

GUI event-listener interfaces

- common interfaces of the java API - specifies one or more methods that must be implemented to respond to user interactions

Serializable

- common interfaces of the java API - used to identify classes whose object can be written to or read from some type of storage (file on disk, database field, etc.) or transmitted from a network.

abstract class

- declare common attributes and behaviors (both abstract and concrete) of the various classes in a hierarchy - typically contains one or more abstract methods that subclasses must override if they are to be concrete.

Runnable

- functional interface to define a task that may be run in parallel with other parts of your program

Comparator

- functional interfaces to define a method that can compare two objects of a given type to determine whether the first object is less than, equal to or greater than the second.

ActionListener

- functional interfaces to define a method that's called when the user clicks a button

Interfaces

- offer a capability requiring that unrelated classes implement a set of common methods - define and standardize the ways in which things such as people and systems can interact with one another

interfaces

- often used when disparate classes (i.e., unrelated classes) need to share common methods and constants - Allows objects of unrelated classes to be processed polymorphically by responding to the same method calls

realization

- used for UML to express relationship between a class and an interface - A class is said to "realize," or implement, the methods of an interface - modeled as a dashed arrow with a hollow arrowhead pointing from the implementing class to the interface

abstract superclasses

Another reference for abstract classes, Used only as superclasses in inheritance hierarchies

functional interface

As of Java SE 8, any interface containing only one abstract method

dynamic binding

At execution time, the type of the object to which the variable refers determines the actual method to use

public default methods

Java SE 8 methods with concrete default implementations that specify how operations are performed when an implementing class does not override the methods

dynamic or late binding

Java decides which class's toString method to call at execution time rather than at compile time

objects of the interface type

Objects of any subclasses of a class that implements an interface

is-a relationship

Once a class implements an interface and all objects of the class are guaranteed to provide the functionality described by the interface

is-a relationship

applies only up the hierarchy from a subclass to its direct (and indirect) superclasses, and not down the hierarchy

interface declaration

begins with the keyword interface and contains only constants and abstract methods - all interface members must be public

superclass reference

can be used to invoke only methods of the superclass

superclass object

cannot be treated as a subclass object - it is not an object of any of its subclasses

default methods

declare common method implementations in interfaces, which gives you more flexibility in designing your classes

downcasting

enables a program to invoke subclass methods that are not in the superclass.

compilation error

error in attempting to invoke a subclass-only method directly on a superclass reference

compilation error

error made attempting to instantiate an object of an abstract class

compilation error

error made when assigning a superclass variable to a subclass variable

compilation error

error made when failure to implement a superclass's abstract methods in a subclass, unless subclass is also declared abstract

compilation error

error resulted in failing to implement any method of an interface in a concrete class that implements the interface - must be declared abstract

compilation error

error where attempting to declare a subclass of a final class

abstract method

is an instance method with keyword abstract in its declaration, as in public abstract void draw(); // abstract method

interface

prior to Java SE 8, was typically used (rather than an abstract class) when there were no implementation details to inherit

getClass method

returns an object Class (from package java.lang), which contains information about the object's type, including its class name

getName

returns the object's class name

ClassCastException

when downcasting a reference, occurs if the referenced object at execution time does not have an is-a relationship with the type specified in the cast operator