所以我正在编写一个程序来求解一个二次方程，除了让 2 个 JLabels（以前是空的）显示答案之外，一切都有效，（当用户单击 JButton 时会发生这种情况）
这是整个程序，因为我不知道错误在哪里。
import java.awt.event.*;
import javax.swing.*;
public class Third implements ActionListener {
//--------------
//Data Members
//--------------
/**
* Top level window
*/
JFrame top;
/**
* Changed into a string by ConvertToDouble(string str);
*/
double a, b, c;
double answer1,answer2;
JTextField inputA, inputB, inputC;
JLabel describeA, describeB, describeC, print1, print2;
JButton submit;
String aa, bb, cc;
String result1, result2;
String strA, strB, strC;
public Third(){
top = new JFrame("Ned's quadratic equation solver");
top.setVisible(true);
top.setLayout(null);
top.setBounds(50,50,250,250);
inputA = new JTextField(12);
inputA.setBounds(100,30,200,25);
inputB = new JTextField(12);
inputB.setBounds(100,105,200,25);
inputC = new JTextField(12);
inputC.setBounds(100,185,200,25);
describeA = new JLabel("Enter A here:");
describeA.setBounds(10,30,200,25);
describeB = new JLabel("Enter B here:");
describeB.setBounds(10,105,200,25);
describeC = new JLabel("Enter C here:");
describeC.setBounds(10,185,200,25);
print1 = new JLabel();
print1.setBounds(15,290,1000,10);
print2 = new JLabel();
print2.setBounds(15,310,1000,10);
submit = new JButton ("WHAT DOES X = ???");
submit.setBounds(50,230,150,25);
submit.addActionListener(this);
top.add(inputA);
top.add(inputB);
top.add(inputC);
top.add(describeA);
top.add(describeB);
top.add(describeC);
top.add(submit);
top.doLayout();
}
public void actionPerformed(ActionEvent event) {
aa = inputA.getText();
bb = inputB.getText();
cc = inputC.getText();
a = convertToDouble(aa);
b = convertToDouble(bb);
c = convertToDouble(cc);
makeAns(a,b,c);
/*
* DEBUG CODE
*
* System.out.println(a);
* System.out.println(b);
* System.out.println(c);
* System.out.println(answer1);
* System.out.println(answer2);
*/
result1 = "x = " + answer1;
result2 = "x = " + answer2;
print1.setText(result1);
print2.setText(result2);
//System.out.println(result1);
top.doLayout();
}
private void makeAns(double x,double y,double z){
answer1 =(-y + Math.sqrt (y*y-4*x*z))/(2*x);
answer2 =(-y - Math.sqrt (y*y-4*x*z))/(2*x);
}
private double convertToDouble (String str) {
Double dubb = new Double(str);
return dubb.doubleValue();
}
}