Perceptron Class

import java.text.DecimalFormat;
import java.util.LinkedList;
import javax.swing.*;
public class Perceptron{
    private int x1=1,x2=1;
    private double w1,w2;
    private int []desired={0,0,0,1};
    private double y=0;
    private double c=0.2,alpha=0.1;
    private double error;
    private StringBuffer st;
    public Perceptron(){

    }

    public void start(){
        st=new StringBuffer();
        boolean exe=true;
        int count=0;

        st.append(" x1  x2| desired |  w1\t  w2\t|actual | error\t|  w1\tw2 \n");
        st.append(" ============================================================ \n");
        while(exe&&count<50){
            exe=false;
            for(int i=0;i<4;i++){
                x2=Math.abs(x2-1); //to generate input,x2 0,1
                if(x2==0){
                    x1=Math.abs(x1-1);//to generate input,x1 0,1
                }
                st.append("  "+x1+"  "+x2+" |     "+desired[i]
                    +"\t | "+String.format("%.1f",w1)+"\t "+String.format("%.1f",w2)+"\t|    " );

                activation();//activation process : y = summation of input(i) x weight(i), minus threshold

                int actual;
                if(y<0){// y is negative
                    actual = 0;
                }
                else{// y is positive
                    actual = 1;
                }
                error=desired[i]-actual;
                if(error!=0){//error occur : error = -1,1
                    exe=true;

                    weightTraining();// weight training : produce new weight
                }
                st.append(actual+"\t| "+error+"\t| "+w1+"  "+w2);
                st.append("\n");
            }
            count++;
            st.append(" ============================================================ \n");
        }
        if(count>=50){
            JOptionPane.showMessageDialog(null,"Program Terminate.\nbecause system can't learn.\n(Infinite Loop)'","Message",JOptionPane.ERROR_MESSAGE);
        }
    }

    public void initialize(double tres,double alpha,double w1, double w2){
        this.w1=Double.parseDouble(String.format("%.1f",w1));
        this.w2=Double.parseDouble(String.format("%.1f",w2));
        this.c=Double.parseDouble(String.format("%.1f",tres));
        this.alpha=Double.parseDouble(String.format("%.1f",alpha));

    }

    public void activation(){
        y=(x1*w1+x2*w2)-c;
    }

    public void weightTraining(){
        DecimalFormat df = new DecimalFormat("#.#");
        Double.parseDouble(df.format(w1));
        w1=Double.parseDouble(df.format(w1+(alpha*error*x1)));
        w2=Double.parseDouble(df.format(w2+(alpha*error*x2)));

    }

    public void reset(){
    }

    public String toString(){
        String str=st.toString();
        return str;
    }

}