JTextField的内容为字符串型想要转换成double型只能在actionPerformed（）中转换，只有这样才不会出错
package Work;
import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
public class exe21 {
public static void main(String args[]) {
MyFrame mf=new MyFrame("计算三角形面积",100,100,1000,750);
JPanel jp=new JPanel();
jp.setLayout(new FlowLayout());
JLabel []jl= {new JLabel("边A:"),new JLabel("边B:"),new JLabel("边C:")};
JTextField jtf1= new JTextField(15);
JTextField jtf2= new JTextField(15);
JTextField jtf3= new JTextField(15);
JButton jb=new JButton("计算面积");
jp.add(jl[0]);
jp.add(jtf1);
jp.add(jl[1]);
jp.add(jtf2);
jp.add(jl[2]);
jp.add(jtf3);
jp.add(jb);
mf.add(jp,BorderLayout.NORTH);
JTextArea jta=new JTextArea();
mf.add(jta,BorderLayout.CENTER);
TriAngle tri=new TriAngle();
tri.setJButton(jb);
tri.setJTextArea(jta);
tri.setValue(jtf1,jtf2,jtf3);
jb.addActionListener(tri);
mf.setVisible(true);
}
}
class MyFrame extends JFrame{
MyFrame(String s,int x,int y,int z,int h){
setTitle(s);
setLayout(new BorderLayout());
setBounds(x,y,z,h);
setDefaultCloseOperation(EXIT_ON_CLOSE);
}
}
class TriAngle implements ActionListener{
double a;
double b;
double c;
double p;
JButton jbu;
JTextArea jea;
JTextField jtd1;
JTextField jtd2;
JTextField jtd3;
void setValue(JTextField a,JTextField b,JTextField c) {
jtd1=a;
jtd2=b;
jtd3=c;//如果是以数组的形式传参会报错
}
double setArea() {
return Math.sqrt(p*(p-a)*(p-b)*(p-c));
}
void setJButton(JButton j) {
jbu=j;
}
void setJTextArea(JTextArea j) {
jea=j;
}
public void actionPerformed(ActionEvent e) {
this.a=Double.parseDouble(jtd1.getText());
this.b=Double.parseDouble(jtd2.getText());
this.c=Double.parseDouble(jtd3.getText());//JTextField的内容为字符串型想要转换成double型只能在actionPerformed中转换，只有这样才不会出错
p=(a+b+c)/2;
if(a+b>c&&a+c>b&&b+c>a) {
jea.append("三角形"+a+" "+b+" "+c+"的面积:"+setArea()+"\n");
}
else jea.append("三角形"+a+" "+b+" "+c+"的面积:无法计算面积"+"\n");
}
}