继承中的方法调用有问题

Question

我在我的程序中使用了实现继承，我的子类中的方法没有在主方法中被调用。它显示了错误“方法getArea（）不在第二类型中定义”。getPerimeter（）方法也有同样的问题。

我试过设置值和改变参数。

package firstproject;
import java.util.Scanner;
import java.util.Date;
import java.util.ArrayList;
public class Second{
  public String color="red" ;
  public boolean filled;
public Second() {

}
public Second(String tcolor, boolean tfilled) {
  tcolor=color;
  tfilled=filled;
}
public String getColor() {
  return color;
}
public boolean getfilled() {
   return filled;
}
public void setColor(String tcolor) {
   tcolor=color; 
}
public void setFilled(boolean tfilled) {
   tfilled=filled;
}
public String toString() {
   return "Color is =" +color+ " and it is filled or not = " 
   +filled;
 }
class myclass extends Second {
   double s1=1.0;
   double s2=1.0;
   double s3=1.0;
public myclass(){

 }
public myclass(double s4, double s5, double s6) {
s4=s1;
s5=s2;
s6=s3;
 }
double gets1() {
return s1;
}

double gets2() {
return s2;
}
double gets3() {
return s3;
}
public void sets1(double s4) {
s4=s1;
}
public void sets2(double s5) {
s5=s2;
}
public void sets3(double s6) {
s6=s3;
}
public double getArea() {
return (s2*s3)/2;
}
public double getPerimeter() {
return s1+s2+s3;
}
}
public static void main(String[] args) {
    System.out.println("Enter the three sides = ");
    Scanner input=new Scanner(System.in);
    int side1=input.nextInt();
    int side2=input.nextInt();
    int side3=input.nextInt();
    Second Triangle= new Second();
    System.out.println("Enter the color = ");
    String colo=input.next();
    System.out.println("The boolean value = ");
    String fil =input.next();
    System.out.println("The area of the triangle is = " 
  +Triangle.getArea());
    System.out.println("The perimeter of the triangle is = " 
  +Triangle.getPerimeter());
    System.out.println("The color in which it is filled is = " 
  +Triangle.getColor());
    System.out.println("If it is filled or not = " 
  +Triangle.getfilled());
}
}

It's showing the error "The method getArea() is not defined in type 
Second". Also, the same stuff is happening with the getPerimeter() 
method. So, I had the question of how to solve the code and is it an   
error related to subclass? The question is something like: 
(The Triangle class) Design a class named Triangle that extends
GeometricObject. The class contains:
■ Three double data fields named side1, side2, and side3 with 
default values
1.0 to denote three sides of the triangle.
■ A no-arg constructor that creates a default triangle.
■ A constructor that creates a triangle with the specified side1, 
side2, and
side3.
■ The accessor methods for all three data fields.
■ A method named getArea() that returns the area of this triangle.
■ A method named getPerimeter() that returns the perimeter of this 
triangle.
■ A method named toString() that returns a string description for 

三角形。有关计算三角形面积的公式，请参见编程练习2.15。toString（）方法的实现如下：return“Triangle:side1=“side1”side2=“side2”side3=“side3；为类三角形和几何对象绘制UML图，并实现这些类。编写一个测试程序，提示用户输入三角形的三条边、颜色和布尔值，以指示三角形是否已填充。程序应该用这些边创建一个三角形对象，并使用输入设置颜色和填充属性。程序应显示面积、周长、颜色以及真或假，以指示是否填充。

Answer 1

实际上，我认为你正在混淆多态性和继承性。

Java继承

Java继承背后的思想是，可以创建基于现有类的新类。从现有类继承时，可以重用父类的方法和字段。此外，还可以在当前类中添加新方法和字段。

继承代表了

Java中的多态性

Java中有两种多态性：编译时多态性和运行时多态性。我们可以通过方法重载和方法重写在java中执行多态性。

如果你在Java中重载一个静态方法，它就是编译时多态性的例子。在这里，我们将关注java中的运行时多态性。

你在这里做的是继承。所以父类方法属性和方法继承给子类，反之亦然。在您的例子中，Second是父类，myClass是Second类的子类。由于getArea方法是在myClass中定义的，它是一个子类，因此父类Second没有关于getArea方法的详细信息。所以你得到了这个错误。