[J2SE] 新手想發問問題>"<

[kagerougogo (源氣)]

各位大神好，我想利用JTextFeild來輸入數字，再用JButton來進行程式運算，
再將計算結果顯示在另外一個JTextFeild上，但一直無法如我想像的寫出，
compiler有過，但一直無法順利進行，我的程式碼如下，可以幫我看看嗎  ˊ ˋ
感謝大神們！

import java.awt.*;
import java.awt.event.*;
import java.text.DecimalFormat;
import javax.swing.*;

public class App7202 extends JApplet implements ActionListener  {
    JTextField number1,formula,number2,total;
    JButton b1;
    int n1=0;
        int n2=0;
        double answer=0;
    String x;
    DecimalFormat F = new DecimalFormat( "0.00" );

    public void init(){
        number1 = new JTextField(6);
        formula = new JTextField(2);
        number2 = new JTextField(6);
        total = new JTextField(6);
        total.setEditable( false );
        b1 = new JButton("=(按我)");
        b1.addActionListener(this);
        Container c =getContentPane();
        FlowLayout fl = new FlowLayout();
        c.setLayout(fl);
        c.add(number1);c.add(formula);c.add(number2);c.add(b1);c.add(total);

    }
    public void actionPerformed( ActionEvent e )
    {
       Fromula();
    }
    public void Fromula(){
        x = formula.getText();
        n1 = Integer.parseInt(number1.getText());
        n2 = Integer.parseInt(number2.getText());
        if (x=="+"){
                answer=n1+n2;
                total.setText(  String.valueOf ((answer)) );
        }
        else if (x=="-"){
                answer=n1-n2;
                total.setText(  String.valueOf ((answer)) );
                }
                else if (x=="*"){
                        answer=n1*n2;
                        total.setText(  String.valueOf ((answer)) );
                }
                else if (x=="/"){
                answer=(double)n1/n2;
                total.setText(  String.valueOf (F.format(answer)) );
                }
                else if (x=="^"){
                        answer=Math.pow(n1, n2);
                        total.setText(  String.valueOf (F.format(answer)) );
                }
    }
}

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