Question

Can someone find what's wrong? If I don't use the last main method Netbeans says that there is no main method. I can't figure out what's wrong.

This was the prompt:

Design a class named triangle that extends geometricObject. For this, you should have created a GeometricObject class first. The class contains:

• Three double datafields named side1, side2, side3 with default value 1.0.
• A no arg constructor that creates a default triangle.
• A constructor that creates a triangle with specified side1, side2 and side3.
• A method named getPerimeter() that returns the perimeter of a triangle.
• A method name toString that returns the string description of a triangle.(including color and filled)

Your main method should create a triangle object and display it using toString()

This is my code:

package geometricobject;

/**
*
*
*/
public class GeometricObject {

/**
* @param args the command line arguments
*/
private String color = "white";
private boolean filled;
private java.util.Date dateCreated;

public GeometricObject() {
dateCreated = new java.util.Date();
}

public GeometricObject(String color, boolean filled) {
dateCreated = new java.util.Date();
this.color = color;
this.filled = filled;
}

public String getColor() {
return color;
}

public void setColor(String color) {
this.color = color;
}

public boolean isFilled() {
return filled;
}

public void setFilled(boolean filled) {
this.filled = filled;
}

public java.util.Date getDatecreated() {
return dateCreated;
}
  
public String toString() {
return "created on" + dateCreated + "\ncolor: " + color+ " and filled: " + filled;
}
  

public class triangle extends GeometricObject
{
private double side1;
private double side2;
private double side3;
  
public triangle() {
side1 = 1;
side2 = 1;
side3 = 1;
}
  
public triangle(double side1, double side2, double side3) {
this.side1 = side1;
this.side2 = side2;
this.side3 = side3;
}
public double getSide1() {
return side1;
}
public double getSide2() {
return side2;
}
public double getSide3() {
return side3;
}
public void setSide1(double side1) {
this.side1 = side1;
}
public void setSide2(double side2) {
this.side2 = side2;
}
public void setSide3(double side3) {
this.side3 = side3;
}
public double getArea() {
double n = (side1+side2+side3) / 2.0;
return Math.sqrt(n*(n-side1)*(n-side2)*(n-side3));
}
public double getPerimeter() {
return side1 + side2 + side3;
}
  
@Override
public String toString() {
return super.toString() + "Triangle: side1 = " + side1 + " side2 = " + side2 + "side3 = " + side3 ;

}}}

Answer 1

Error details :

• For testing triangle class need to write a driver class then only error will be resolved
• need a main() method to in the class.

*****************************

NOTE :NO CHANGE MADE IN THE CLASS GeometricObject.java

triangle.java :

package geometricobject;

//Java class
public class triangle extends GeometricObject {
   //datafields
   private double side1;
   private double side2;
   private double side3;
   //no arg constructor
   public triangle() {
       this.side1 = 1.0;
       this.side2 = 1.0;
       this.side3 = 1.0;
   }
   //constructor with parameters
   public triangle(double side1, double side2, double side3) {
       this.side1 = side1;
       this.side2 = side2;
       this.side3 = side3;
   }

   public double getSide1() {
       return side1;
   }

   public double getSide2() {
       return side2;
   }

   public double getSide3() {
       return side3;
   }

   public void setSide1(double side1) {
       this.side1 = side1;
   }

   public void setSide2(double side2) {
       this.side2 = side2;
   }

   public void setSide3(double side3) {
       this.side3 = side3;
   }

   public double getArea() {
       double n = (side1 + side2 + side3) / 2.0;
       double area=n * (n - side1) * (n - side2) * (n - side3);
       double a=Math.sqrt(area);
       return a;
   }
   //A method named getPerimeter() that returns the perimeter of a triangle.
   public double getPerimeter() {
       return side1 + side2 + side3;
   }
   //A method name toString that returns the string description of a triangle.(including color and filled)
   @Override
   public String toString() {
       return super.toString() + "\nTriangle: side1 = " + side1 + " side2 = " + side2 + " side3 = " + side3;

   }
}
***********************************************'

triangleTest.java :

package geometricobject;

//Java class
public class triangleTest {
   // main() method
   public static void main(String[] args) {
       // Object of triangle class
       triangle t = new triangle(3.0, 5.0, 7.0);
       // call method to print area of triangle
       System.out.println("Area of triangle : " + t.getArea());
       // call method to print perimeter
       System.out.println("Perimeter of triangle : " + t.getPerimeter());
       System.out.println(t.toString());
   }

}
======================================

Output :