问题描述:
import java.awt.*
import java.awt.event.*
import javax.swing.*
自定义异常类
class NumException extends Exception{
public String toString(){
return "输入的值太小"
}
public String shuru(){
return "请输入数字"
}
}
class jisuanqi extends JFrame implements ActionListener,ItemListener{
JRadioButton rz
JRadioButton rm
ButtonGroup bg
JTextField txt
JButton btnj
String msg
jisuanqi(){
super("计算器")
rz=new JRadioButton("周长")
rm=new JRadioButton("面积")
bg=new ButtonGroup()
txt=new JTextField()
btnj=new JButton("计算")
msg=""
this.getContentPane().setLayout(new GridLayout(2,2))
bg.add(rz)
bg.add(rm)
this.getContentPane().add(rz)
this.getContentPane().add(rm)
this.getContentPane().add(txt)
this.getContentPane().add(btnj)
this.setSize(200,200)
rz.addItemListener(this)
rm.addItemListener(this)
btnj.addActionListener(this)
}
实现接口
public void actionPerformed(ActionEvent e) throws NumException{声明异常
if (Double.parseDouble(txt.getText())<=0){
throw new NumException()抛出异常
}
if (msg.equals("周长")){
txt.setText(""+(3.14*2*Double.parseDouble(txt.getText())))
}
if (msg.equals("面积")){
txt.setText(""+3.14*(Double.parseDouble(txt.getText())*Double.parseDouble(txt.getText())))
}
}
实现接口
public void itemStateChanged(ItemEvent e){
if (e.getSource()==rz){
msg="周长"
}
if (e.getSource()==rm){
msg="面积"
}
}
public static void main(String args[]){
try{
jisuanqi js=new jisuanqi()
js.setVisible(true)
}
catch(NumException ex){
System.out.println(ex)
}
}
}
编译时出现：
C:\Documents and Settings\Administrator\桌面\新建文件夹\jisaunqi.java:45: jisuanqi 中的 actionPerformed(java.awt.event.ActionEvent) 无法实现 java.awt.event.ActionListener 中的 actionPerformed(java.awt.event.ActionEvent)；被覆盖的方法不抛出 NumException
解析:
这段代码有问题：
实现接口
public void actionPerformed(ActionEvent e) throws NumException{声明异常
public void actionPerformed(ActionEvent e)不应该抛出异常， ActionListener接口函数没有异常抛出
一种可能的解决方法是把判断移到另外一个函数中，然后抛出异常，在actionPerformed中捕获或者在外面捕获
public class Bank {private Integer moneyTotal
//存款
public Integer saveMoney(Integer moneyConut) throws Exception {
if(moneyConut<0){
throw new Exception("存款异常")
}
return moneyConut+moneyTotal
}
//取款
public Integer getMoneyCoun(Integer moneyCount) throws Exception {
if(moneyTotal-moneyCount<0){
throw new Exception("取款异常")
}
return moneyTotal-moneyCount
}
}
