我这个计算器的变量赋值有问题，获取的值是0.0该怎么写呢？

Question

import java.awt.EventQueue;

import javax.swing.JFrame;

import javax.swing.JPanel;

import javax.swing.border.EmptyBorder;

import java.awt.TextField;

import java.awt.Color;

import javax.swing.JTextField;

import java.awt.TextArea;

import javax.swing.JButton;

import java.awt.event.ActionListener;

import java.awt.event.ActionEvent;

import java.awt.Button;

import javax.swing.JTree;

import javax.swing.JLabel;

public class Demo extends JFrame {

private JTextField txt=new JTextField();

private JPanel contentPane;

double text1=0;

     double text2=0;

final TextField textField,textField_1;

/**

* Launch the application.

*/

public static void main(String[] args) {

EventQueue.invokeLater(new Runnable() {

public void run() {

try {

Demo frame = new Demo();

frame.setVisible(true);

} catch (Exception e) {

e.printStackTrace();

}

}

});

}

/**

* Create the frame.

*/

public Demo() {

  /*  final double text1;

    final double text2;

final TextField textField,textField_1;*/

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

setBounds(100, 100, 450, 300);

contentPane = new JPanel();

contentPane.setToolTipText("");

contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));

setContentPane(contentPane);

contentPane.setLayout(null);

textField = new TextField();

textField.setBounds(68, 61, 99, 23);

contentPane.add(textField);

if(textField.getText()!=null&&textField.getText().length()>0){

text1=Double.parseDouble(textField.getText().trim());  

}

textField_1 = new TextField();

textField_1.setBounds(247, 61, 99, 23);

contentPane.add(textField_1);

if(textField_1.getText()!=null&&textField_1.getText().length()>0){

text2=Double.parseDouble(textField_1.getText().trim());

}

Button add = new Button("+");

add.setBounds(68, 115, 33, 23);

contentPane.add(add);

add.addActionListener(new ActionListener(){

@Override

public void actionPerformed(ActionEvent e) {

// TODO Auto-generated method stub

txt.setText(text1+text2+"");

}

});

Button button_1 = new Button("-");

button_1.addActionListener(new ActionListener() {

public void actionPerformed(ActionEvent e) {

txt.setText((text1-text2)+"");

}

});

button_1.setBounds(139, 115, 33, 23);

contentPane.add(button_1);

Button button_3 = new Button("/");

button_3.setBounds(313, 115, 33, 23);

contentPane.add(button_3);

Button button_4 = new Button("*");

button_4.setBounds(247, 115, 33, 23);

contentPane.add(button_4);

txt.setBounds(68, 166, 278, 23);

contentPane.add(txt);

JButton btnNewButton = new JButton("清零");

btnNewButton.setBounds(68, 209, 73, 23);

contentPane.add(btnNewButton);

JButton btnNewButton_1 = new JButton("退出");

btnNewButton_1.addActionListener(new ActionListener() {

public void actionPerformed(ActionEvent e) {

}

});

btnNewButton_1.setBounds(273, 209, 73, 23);

contentPane.add(btnNewButton_1);

JLabel label = new JLabel("请输入两个运算数据");

label.setBounds(68, 10, 130, 45);

contentPane.add(label);

}

}