macOS Java: run time exceptions

What could be the cause of such a message:

java.lang.NoSuchMethodError: mainException in thread "main" ?

robbieduncan said:

You've tried to call a method on an Object that does not support that method most likely.

Click to expand...

Would you, please, mind checking the code?


class TwoDShape{
private double width;
private double height;

double getWidth(){return width;}
double getHeight(){return height;}
void setWidth(double w){width=w;}
void setHeight(double h){height=h;}
void showDim(){
System.out.println("Width and height are "+width+" and "+height);

}
}
class Triangle extends TwoDShape{
private String style;

Triangle(String s, double w, double h){
setWidth(w);
setHeight(h);
style=s;
}
double area(){
return getWidth()*getHeight()/2;

}
void showStyle(){
System.out.println("Triangle is "+style);
}
}
class Shapes{
public static void main(String args[]){
Triangle t1=new Triangle("isosceles", 4.0, 4.0);
Triangle t2=new Triangle ("right", 8.0, 12.0);

System.out.println("Info for t1: ");
t1.showStyle();
t2.showDim();
System.out.println("Area is "+t1.area());
System.out.println();

System.out.println("Info for t2: ");
t2.showStyle();
t1.showDim();
System.out.println("Area is "+ t2.area());
}
}

hsvmoon said:

check your code for casting that is not correct. you might create an object cast it into a variable that is a super class to the object and then call a method only the child class has.

Click to expand...

I've just started learning inheritance. First day today. Your advise sounds a bit complicated. In how many steps should I be able to do this?

robbieduncan said:

The code looks OK as far as I can see by eye: I'm not about to compile and fix it especially as this looks like a very basic homework assignment. A very important part of programming is being able to debug your code.

Can you copy and paste exactly including the spacing (which is important as I believe you have removed a space or new line in your original post) the command you issue in the terminal and the entire response?

Click to expand...

No, it's not a homework. I'm studying on my own.

Don't laugh, but I don't know such a basic thing like how to copy the code with all the spaces. I'd like to learn it. What do I do?

Eraserhead said:

First put each class into a seperate file.

Then put import className; at the top to import the other class files.

Click to expand...

I separated class Shapes from the rest of two classes. I can compile them separately. However as soon as I type import class-name ,-compiler indicates errors.

lazydog said:

You don't have a main() function. Well you do but the class TwoDShape needs a main(). When you run your program Java will look for a main() function in the main class. The main class is the one that has the same name as the program. Hence the error message you are getting.

b e n

Click to expand...

I will check if that's the case.

lazydog said:

Sorry happyElephant, I was assuming your file is called TwoDShape.java

Looking at your code again I think the problem is is that your file should be called Shapes.java. What did you call it?

b e n

Click to expand...

It's called : TwoDShape. I changed the filename to "Shapes"&it worked!!!

thank you!!!


and thanks everybody who tried to help me