Please help me with this Java programming

Hello everyone I am a BSC Mathematics student and very beginner in Java Programming and as part of my Mathematics degree I am also learning Algorithm with Java programming. I am in very early stages of Java so I could be making very silly mistake but believe it or not but I am stuck with this error for last 2 days but still cannot figure out where is the problem. Anyone please help me I will really appreciate that.

Following is the programme code I am using:

Code :

---

import java.io.*;
import javagently.*;
 
class CW2Q1
{
	//Main program to run the Gaussian Quadrature.
 
		   public static void main(String[] args) throws IOException
			{
 
					Gauss_Quadrature_Data = new Gauss_Quadrature_Data();
					Gauss.input_data();
					Gauss.cal_x();
					Gauss.cal_fx();
					Gauss.cal_sum();
					Gauss.store_x_output();
					Gauss.store_f_output();
 
					BufferedReader user_keyin= Text.open(system.in);
 
					System.out.print("What is your a");
						int input_a = Text.readint(user_keyin);
					System.out.print("What is your b");
						int input_b = Text.readint(user_keyin);
					System.out.print("What is your n");
						int input_n = Text.readint(user_keyin);
			}
 
 
		static class Gauss_Quadrature_Data
		{         
			        double sum, x, fx;
					int n=0; n<=3; n++;
 
									 if (n==0); {
										double [] []  t; c = new double[0.5773502692, -0.5773502692; 1.0000000000, 1.0000000000];
									} else
									if n==1); {
									double [] [] t; c = new double[0.7745966692,	 0.0000000000, -0.7745966692; 0.5555555556, 0.8888888889, 0.5555555556];
									}else
									if (n==2); {
										double [] [] t; c = new double[0.8611363116, 0.3399810436, -0.3399810436, -0.8611363116; 0.3478548451, 0.6521451549, - 0.6521451549, - 0.3478548451];
									} else
									if (n==3); {
										double [] [] t; c =new double[0.9061798459, 0.5384693101, 0.0000000000, -0.5384693101, -0.9061798459;  0.2369268850, 0.4786286705, 0.5688888889, 0.4786286705, 0.2369268850];
									 }
		}
 
		void input_data() throws IOException
		{
			//BufferedReader user_keyin = Text.open(System.in);
			//System.out.print("User please key in the arraysize:");
			BufferedReader user_file = Text.open("CW2Q1_data.txt");
		}
 
		void cal_x()
		{
				cal_x = ((b-a)*(double)(t)+b+a)/2;
				return cal_x;
		 }
 
		void cal_fx()
		{
				cal_fx = Math.pow(x[t],2)*math.sin (x[t])*(b-a)/2;
				return cal_fx;
		}
 
		void cal_sum()
		{ // this section calculates the sum of a product c*fx
			double cal_sum(double fx, double c)
			 sum = 0.0;
			double cal_sum = sum + (double)(c)*(double)(fx);
			return cal_sum;
		}
}

---

PLEASE HELP AS I NEED TO HAND THIS IN ON FRIDAY AND IT'S 50% OF MY ASSIGNMENT PLEASE HELP :((

what's your problem here?

Code :

---

import java.io.*; 
 
public class CW2Q1 {
 
    public static void main(String[] args)throws IOException {
    	Gauss_Quadrature_Data = new Gauss_Quadrature_Data();
					Gauss.input_data();
					Gauss.cal_x();
					Gauss.cal_fx();
					Gauss.cal_sum();
					Gauss.store_x_output();
					Gauss.store_f_output();
 
					BufferedReader user_keyin= Text.open(system.in);
 
					System.out.print("What is your a");
						int input_a = Text.readint(user_keyin);
					System.out.print("What is your b");
						int input_b = Text.readint(user_keyin);
					System.out.print("What is your n");
						int input_n = Text.readint(user_keyin);
			}
 
 
		static class Gauss_Quadrature_Data
		{         
			        double sum, x, fx;
				for (int n=0; n<=3; n++;){
				}
 
									 if (n==0) {
										double [] []  t; c = new double[0.5773502692, -0.5773502692; 1.0000000000, 1.0000000000];
									} else
									if n==1) {
									double [] [] t; c = new double[0.7745966692,	 0.0000000000, -0.7745966692; 0.5555555556, 0.8888888889, 0.5555555556];
									}else
									if (n==2) {
										double [] [] t; c = new double[0.8611363116, 0.3399810436, -0.3399810436, -0.8611363116; 0.3478548451, 0.6521451549, - 0.6521451549, - 0.3478548451];
									} else
									if (n==3) {
										double [] [] t; c =new double[0.9061798459, 0.5384693101, 0.0000000000, -0.5384693101, -0.9061798459;  0.2369268850, 0.4786286705, 0.5688888889, 0.4786286705, 0.2369268850];
									 }
		}
 
		void input_data() throws IOException
		{
			//BufferedReader user_keyin = Text.open(System.in);
			//System.out.print("User please key in the arraysize:");
			BufferedReader user_file = Text.open("CW2Q1_data.txt");
		}
 
		void cal_x()
		{
				cal_x = ((b-a)*(double)(t)+b+a)/2;
				return cal_x;
		 }
 
		void cal_fx()
		{
				cal_fx = Math.pow(x[t],2)*math.sin (x[t])*(b-a)/2;
				return cal_fx;
		}
 
		void cal_sum()
		{ // this section calculates the sum of a product c*fx
			double cal_sum(double fx, double c)
			 sum = 0.0;
			double cal_sum = sum + (double)(c)*(double)(fx);
 
		}
}
 
}

---

here is my code for you.. I reduce some errors ?
but Still It has an error..
hope it little bit help you..^^,

first let me know what you are trying to do

i think you just copied some where and posted it here, first you need to know the basics.