代码：
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class EquationFrame extends JFrame implements ActionListener {
SquareEquation equation;
JTextField textA, textB, textC;
JTextArea showRoots;
JButton controlButton;
public EquationFrame() {
equation = new SquareEquation();
textA = new JTextField(8);
textB = new JTextField(8);
textC = new JTextField(8);
controlButton = new JButton("确定");
JPanel pNorth = new JPanel();
pNorth.add(new JLabel("二次项系数:"));
pNorth.add(textA);
pNorth.add(new JLabel("一次项系数:"));
pNorth.add(textB);
pNorth.add(new JLabel("常数项系数:"));
pNorth.add(textC);
pNorth.add(controlButton);
controlButton.addActionListener(this);
getContentPane().add(pNorth, BorderLayout.NORTH);
showRoots=new JTextArea();
JScrollPane scrollPane =new JScrollPane(showRoots);
getContentPane().add(scrollPane,BorderLayout.CENTER);
setSize(630, 160);
Dimension scnSize = Toolkit.getDefaultToolkit().getScreenSize();
Dimension fromSize = this.getSize();
this.setLocation((scnSize.width - fromSize.width) / 2,
(scnSize.height - fromSize.height) / 2);
validate();
setVisible(true);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public void actionPerformed(ActionEvent e) {
try {
double a = Double.parseDouble(textA.getText());
double b = Double.parseDouble(textB.getText());
double c = Double.parseDouble(textC.getText());
equation.setA(a);
equation.setB(b);
equation.setC(c);
showRoots.append("根：" + equation.getRootOne());
showRoots.append("根：" + equation.getRootTwo() + "\n");
} catch (Exception ex) {
showRoots.append(ex.getMessage() + "\n");
}
}
public static void main(String args[]) {
new EquationFrame();
}
}
public class SquareEquation {
double a, b, c;
public void setA(double a) {
this.a = a;
}
public void setB(double b) {
this.b = b;
}
public void setC(double c) {
this.c = c;
}
public double getRootOne() {
double disk = calculateValidDisk();
return (-b + Math.sqrt(disk)) / (2 * a);
}
public double getRootTwo() {
double disk = calculateValidDisk();
return (-b + Math.sqrt(disk)) / (2 * a);
}
private double calculateValidDisk() {
if (a == 0) {
throw new EquationException("不是二次方程",
EquationException.NONE_EQUATION);
}
double disk = b * b - 4 * a * c;
if (disk < 0) {
throw new EquationException("没有实根", EquationException.NO_REAL_ROOT);
}
return disk;
}
}
class EquationException extends RuntimeException {
public static final int NONE_EQUATION = 1;
public static final int NO_REAL_ROOT = 2;
private int errorCode;
public EquationException(String msg, int errorCode) {
super(msg);
this.errorCode = errorCode;
}
public int getErrorCode() {
return errorCode;
}
}运算结果：
java一元二次方程程序设计实验报告_Java 组件及事件处理实训 实训2：编写一个窗体程序 用于计算一元二次方程...
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