Why do I get the error "Reached end of file while parsing"?

import javax.swing.JOptionPane;
class Overload
{
    void average(int a, int b, int c)
    {
        average= (a+b+c)/3;
    }
    void average(int d, int e, double a, double b)
    {
        average= (d+e+a+b)/4;
    }
    void average(double c,double d,double e,double f,double g)
    {
        average= (c+d+e+f+g)/5;
}

class mainOverload
{
    public static void main(String args[])
    {
        Overload object=new Overload();
        object.average(7, 5, 1);
        object.average(15, 12, 15.12, 12.15);
        object.average(7.7, 8.4, 30.2, 1.4, 6.4);
    }
}

You forgot to close the 3rd average method:

void average(double c,double d,double e,double f,double g)
    {
        average= (c+d+e+f+g)/5;
    } // << here

Regarding your comment - you haven't declare a variable called average and yet you try to use it in each of the average methods. Declare this variable as a class field or a method field to solve this.

You are missing the closing brace of the method average with 5 double parameters.

This way the compiler interprets the class closing brace as the method closing brace, mainOverload as a nested class and is missing the final closing brace for the Overload class.

Because you forgot the closing bracket } for the class Overload

You are missing a closing parenthesis for the

average(double c,double d,double e,double f,double g)

method. This should be

void average(double c,double d,double e,double f,double g)
    {
        average= (c+d+e+f+g)/5;
    }//Missing!

A bracket is left here

     {
            average= (c+d+e+f+g)/5;
     } // !!!
}

have this new ERROR. "cannot find symbol variable average"...

The problem is that you are assigning to a variable that you haven't declared.

void average(double c,double d,double e,double f,double g)
{
    average= (c+d+e+f+g)/5;  // <<<=== you haven't declared the 'average' variable.
}

But even if you do, your average methods don't make a lot of sense. It would be better to declare the methods as returning the average or their arguments; e.g.

double average(double c,double d,double e,double f,double g)
{
    return (c+d+e+f+g)/5;
}

and then call them like this (for example)

System.out.println(average(7.7, 8.4, 30.2, 1.4, 6.4));

oh man...java give me lot of error...im new in Java ... :(

Yup. You seem to be trying to learn by trial and error. This is a BAD IDEA. It will be slow and frustrating, and you will fail to recognize / understand important concepts and practices that are second nature to properly educated programmers.

You need to buy and read a Java textbook and do the exercises.

(For instance, your text book will explain how you can avoid having to write a bazillion different average methods with different numbers and types of arguments.)