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Accessing Private Attributes and Invoking Inherited Methods in Java: A Guide, Slides of Java Programming

Chandra Shekhar Azad University of Agriculture & Technology Java Programming

An overview of accessing private attributes from ancestor classes and invoking inherited methods of the same name in java. It covers the use of protected modifier, super keyword, and strategies for creating classes for different types of rocks. The document also includes examples and coding instructions.

Typology: Slides

2011/2012

Uploaded on 07/07/2012

kolii 🇮🇳

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Accessing Private Information from an

Ancestor Class

When the ancestor class declares an

attribute as private

both users and descendents of the class are

prevented from accessing the attribute

Java provides the protected modifier

users of the class are prevented

descendents of the class are allowed to

access the attribute

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Accessing Private Information from an

Ancestor Class

 When the ancestor class declares an

attribute as private

 both users and descendents of the class are

prevented from accessing the attribute

 Java provides the protected modifier

 users of the class are prevented

 descendents of the class are allowed to

access the attribute

Invoking an Inherited Method

of the Same Name

 We know that an inherited method can be

overridden by another method of the same

name

 most local (overriding) method takes precedence

 Occasionally we wish to call the inherited

method

 If B extends A and both have a method m()

 The m() method for A can be called from inside B

 Use the syntax super.m()

Objects

Object Type Kind Name

A rock Rock^ varying aRock

chalk Chalk^ constant

shale Shale^ constant

......

description String^ varying aRock.getDescription()

We need classes for

each kind of rock

Strategy

 Create a class for each kind of rock

 Note that classification is a characteristic

Accessing Private Attributes and Invoking Inherited Methods in Java: A Guide, Slides of Java Programming

Related documents

Partial preview of the text

Download Accessing Private Attributes and Invoking Inherited Methods in Java: A Guide and more Slides Java Programming in PDF only on Docsity!

Accessing Private Information from an

Ancestor Class

 When the ancestor class declares an

attribute as private

 both users and descendents of the class are

prevented from accessing the attribute

 Java provides the protected modifier

 users of the class are prevented

 descendents of the class are allowed to

access the attribute

Invoking an Inherited Method

of the Same Name

 We know that an inherited method can be

overridden by another method of the same

name

 most local (overriding) method takes precedence

 Occasionally we wish to call the inherited

method

 If B extends A and both have a method m()

 The m() method for A can be called from inside B

 Use the syntax super.m()

Objects

We need classes for

each kind of rock

Strategy

 Create a class for each kind of rock

 Note that classification is a characteristic

of rocks

 represent classification with a String

attribute

 supply a getClassification() method

 Summarize relationships with class

hierarchy diagram

Operations

At the very least, each class should have:

 A constructor

 Accessor methods for class attributes

 A toString() method to facilitate output

Also:

 getDescription() method in each class

 Attribute variable and accessor for which of the

three categories

Coding

 Class declarations, Figures 11.

through 11.

 Algorithm

1. Prompt user for name of rock

2. Read name into rockString

3. Build instance of class whose name is

stored in rockString

4. Display result of sending that object the

getDescription() message

Constructing an Object from a String

 Returns instance of class whose name stored in

StringVariable

 Created using default constructor of that class

 newInstance returns that instance as an Object

 It must be cast into appropriate type (usually nearest

ancestor)

Form:

class.forName(StringVariable).newInstance()

Where:

StringVariable refers to a String containing

the name of a class

Purpose:

11.4 Example: An O-O Payroll Program

 Consider a program to generate monthly

paychecks for employees.

 Includes different kinds of workers, paid

different ways

 managers & programmers, salary

 secretaries & consultants, hourly

 Program should read sequence of

employees from file, compute pay, print

paycheck

Analysis