Презентация на тему 4. Java OOP. 4. Inheritance and Polymorphism

from other classes, thereby inheriting fields and methods from

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derived from another class is called a subclass (also

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the members (fields, methods, and nested classes) from its

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and protected members of its parent, no matter what

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can declare a field in the subclass with the

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v1 = 8;
protected double p = -5.0;

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Class C{
public static void main(String[] args) {
B obj = new B();
obj.doSomething();
}
}

v1 = 8;
protected double p = -5.0;

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Class C{
public static void main(String[] args) {
B obj = new B();
obj.doSomething();
}
}

Compilation error

v1 = 8;
protected double p = -5.0;

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Class C{
public static void main(String[] args) {
B obj = new B();
obj.doSomething();
}
}

v1 = 8;
protected double p = -5.0;

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Class C{
public static void main(String[] args) {
B obj = new B();
obj.doSomething();
}
}

-5.0

v1 = 8;
protected double p = -5.0;

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Class C{
public static void main(String[] args) {
B obj = new B();
obj.doSomething();
}
}

v1 = 8;
protected double p = -5.0;

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Class C{
public static void main(String[] args) {
B obj = new B();
obj.doSomething();
}
}

8 if B and A in the same package; Compilation error otherwise

as they are.
You can declare new methods in the

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v1 = 8;
protected void printV1(){
System.out.println(v1);

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Class C{
public static void main(String[] args) {
B obj = new B();
obj.printV1();
obj.doSomething();
}
}

v1 = 8;
protected void printV1(){
System.out.println(v1);

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Class C{
public static void main(String[] args) {
B obj = new B();
obj.printV1();
obj.doSomething();
}
}

8 16

instance method in the subclass that has the same

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invokes the constructor of the superclass, either implicitly or

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inherit the private members of its parent class.
However,

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projects with help of ancestor DepoBase class (should contain

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Date startDate;
protected int dayLong;
protected double sum;
protected double interestRate;

public DepoBase()

start, LocalDate maturity){
int startYear = start.getYear();
int maturityYear = maturity.getYear();

}
public DepoSimple(Date startDate, int dayLong, double sum, double interestRate){
super(startDate,

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full text

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of an object of one type in place of

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compiler to assign a ClassName to obj by explicit

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a logical test as to the type of a

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v1 = 8;
protected void printV1(){
System.out.println(v1);

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Class C{
public static void main(String[] args) {
A obj = new B();
obj.printV1();
obj.doSomething();
}
}

v1 = 8;
protected void printV1(){
System.out.println(v1);

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Class C{
public static void main(String[] args) {
A obj = new B();
obj.printV1();
obj.doSomething();
}
}

Compilation error “Undefined method” on line obj.doSomething();

v1 = 8;
protected void printV1(){
System.out.println(v1);

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Class C{
public static void main(String[] args) {
B obj = new A();
obj.printV1();
obj.doSomething();
}
}

v1 = 8;
protected void printV1(){
System.out.println(v1);

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Class C{
public static void main(String[] args) {
B obj = new A();
obj.printV1();
obj.doSomething();
}
}

Compilation error “Type mismatch” on line B obj = new A();

v1 = 8;
protected void printV1(){
System.out.println(v1);

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Class C{
public static void main(String[] args) {
B obj = (B)new A();
obj.printV1();
obj.doSomething();
}
}

v1 = 8;
protected void printV1(){
System.out.println(v1);

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Class C{
public static void main(String[] args) {
B obj = (B)new A();
obj.printV1();
obj.doSomething();
}
}

Runtime error “ClassCastException” on line B obj = (B)new A();

v1 = 8;
protected void printV1(){
System.out.println(v1);

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Class C{
public static void main(String[] args) {
B obj = new B();
A objA = obj;
objA.printV1();
}
}

v1 = 8;
protected void printV1(){
System.out.println(v1);

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Class C{
public static void main(String[] args) {
B obj = new B();
A objA = obj;
objA.printV1();
}
}

8

subclass with the same signature and return type as

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might want to use the @Override annotation that instructs

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v1 = 8;
protected void printV1(){
System.out.println(v1);

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Class C{
public static void main(String[] args) {
B obj = new B();
obj.printV1();
}
}

v1 = 8;
protected void printV1(){
System.out.println(v1);

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Class C{
public static void main(String[] args) {
B obj = new B();
obj.printV1();
}
}

16

{
public static void testClassMethod() {
System.out.println("The class method

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extends Animal {
public static void testClassMethod() {
System.out.println("The

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main(String[] args) {
Animal myAnimal = new Animal();

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in Animal
The instance method in Cat
The instance method in

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main(String[] args) {
Animal myAnimal = new Animal();

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in Animal.
The class method in Animal.
The class method in

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a method body is called binding
When binding is performed

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uses late binding unless the method is static or

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and calculate sum of their interest values
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Sum

Calendar.SEPTEMBER, 8).getTime();
DepoBase[] depo = new DepoBase[6];
depo[0] = new DepoSimple(start,

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depo) sum += d.getInterest();
sum = Math.round(sum * 100) /

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project for the full text
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the same name as a field in the superclass

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a superclass constructor is
super(); or: super(parameter list);
Invocation

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not explicitly invoke a superclass constructor, the Java compiler

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its superclass's methods, you can invoke the overridden method

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a method declaration to indicate that the method cannot

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class that is declared final cannot be subclassed
This is

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