Inherited Classes in Java CSCI 392 Classes Part

Inherited Classes in Java CSCI 392 Classes - Part 2

Recap from last week… n Scope of Fields and Methods can be n public, private, protected n Constructors n syntax is just like C++ n optional since fields can be initialized n "static" fields and methods belong to the entire class, not individual instances

What is Inheritance? n Building a new class by reusing everything in an existing class. n Subclasses can add to their base class's list of methods and fields, and can also replace inherited methods. Animal Fish Mammal

Why use Inheritance? n So that you don't have to rewrite a bunch of code. n Better Maintenance: Correcting/Improving code in the base class fixes all the subclasses.

Declaring an Inherited Class public class stack extends list { The new stack class is a subclass of the list class

What gets Inherited? n All fields marked as "protected" or "public". n "private" fields are only visible to the class that declared them n "protected" fields are only visible to the class that declared them, and any subclasses n All methods marked protected or public.

public class list { protected int[] values; private int size; . . . public class stack extends list {. . . public void some_method () { values[i] = myinteger; // legal size++; // illegal

Jargon Alert n Overloading n creating multiple methods with the same n example: multiple constructors may have the same name if they have different parameters n Overriding n replacing inherited methods n example: see next page

public class Super. Class { public void method 1 () {. . . } public void method 1 (int param 1) {. . . } public void method 2 () {. . . } } public class Sub. Class extends Super. Class { public void method 1 () {. . . } public void method 2 (int param 2) {. . . } } Override Overload

public class Super. Class { public void method 1 () {. . . } public void method 1 (int param 1) {. . . } public void method 2 () {. . . } } public class Sub. Class extends Super. Class { public void method 1 () {. . . } public void method 2 (int param 2) {. . . } }. . . Sub. Class bob = new Sub. Class(); bob. method 1(); bob. method 2(); bob. method 1(99);

Using the Parent's Constructor public class Parent. Class { public Parent. Class (int param) { do a bunch of work }. . . } ================= public class Child. Class extends Parent. Class { public Child. Class (int param) { super (param) }