Java Object-oriented (polymorphic)

Polymorphic: Improves code extensibility, maintainability, the same reference type, and different operations with different instances.

Two implementations: ① the parent class as a method parameter to implement polymorphism ② using the parent class as the method return value.

Implementing polymorphic Two features ① subclasses overriding a parent class ② a parent class reference to a

Parent f=new Child ();

Properties See left

method, compile to see left run see right

For subclass-specific methods, down

Sub-z= (child) F;

Polymorphic use: ① Create a parent class variable, instantiate a subclass object

② the parent type as a parameter type, and the subclass and subclass object are passed in as parameters

③ using the parent class as the return value of the method

/*1, using polymorphic implementation of the subtraction calculator,

* Calculation of different subclasses based on operator different instantiation (operator can receive input by keyboard)

For example: addition has num1, num2 attribute, method: Calculate sum

Subtraction has NUM1, num2 properties, Method: Calculate the difference */

public class Test05 {

public static void Main (string[] args) {

System.out.println ("Please enter an operator");

Scanner input = new Scanner (system.in);

String oparator = Input.next ();

while (!oparator.equals ("+") &&!oparator.equals ("-") &&!oparator.equals ("*") &&! Oparator.equals ("/")) {

SYSTEM.OUT.PRINTLN ("You entered the operator incorrectly, please re-enter");

Oparator = Input.next ();

}

Double result = 0.0;

Operation op = null;

Switch (oparator) {

Case "+":

op = new Add (4, 2);

Break

Case "-":

op = new Subtract (4, 2);

Break

Case "*":

op = new Mul (4, 2);

Break

Case "/":

op = new Div (4, 2);

Break

}

result = calculation.cal (OP);

SYSTEM.OUT.PRINTLN (result);

}

}

Class Calculation {

public static double Cal (Operation op) {

return Op.calculate ();

}

}

Class Operation {

Double NUM1;

Double num2;

Public operation () {

}

Public operation (double NUM1, double num2) {

Super ();

THIS.NUM1 = NUM1;

this.num2 = num2;

}

Public double Calculate () {

return 0.0;

}

}

Class Add extends Operation {

Public Add (double NUM1, double num2) {

Super (NUM1, num2);

}

@Override

Public double Calculate () {

TODO auto-generated Method Stub

return NUM1 + num2;

}

}

Class Subtract extends Operation {

Public Subtract (double NUM1, double num2) {

Super (NUM1, num2);

}

@Override

Public double Calculate () {

return num1-num2;

}

}

Class Mul extends Operation {

Public Mul (double NUM1, double num2) {

Super (NUM1, num2);

}

@Override

Public double Calculate () {

return NUM1 * NUM2;

}

}

Class Div extends Operation {

Public Div (double NUM1, double num2) {

Super (NUM1, num2);

}

@Override

Public double Calculate () {

return num1/num2;

}

}

Java Object-oriented (polymorphic)