eopt.java

Java程序设计大学教程程序源代码

/*
 * EOpt.java
 *
 * Created on 2005年7月28日, 上午9:14
 */

package jbookch9;
import java.io.*;


public class EOpt {
    
    public static void main(String argv[]) throws IOException {
        
        BufferedReader input = new BufferedReader
                (new InputStreamReader(System.in));
        boolean loop=true;
        double x=0,y=0,z=0;
        char c='+';
        //循环
        do {
            try{
                System.out.println("请输入x值:");
                x = Double.parseDouble(input.readLine());
                System.out.println("请输入y值:");
                y = Double.parseDouble(input.readLine());
                System.out.println("输入四则运算符");
                c =(input.readLine()).charAt(0);
                switch (c) {
                    case  '+':z=x+y ;break;
                    case  '-':z=x-y ;break;
                    case  '*':z=x*y;break;
                    case  '/':z=x/y;break;
                    default:throw new EOperatorError("操作符不对！");//抛出操作符错误异常
                };
                System.out.println("x"+c+"y="+z);
            } catch(EOperatorError e){
                //EOperatorError是自定义的异常类
                System.out.println(e.getMessage());
            } catch(NumberFormatException  e){
                //EInOutError是Java现成的异常类
                System.out.println("输入的不是数值！");
            } finally{
                System.out.println("继续吗？(输入no退出,输入其他则继续。)");
                if (input.readLine().equals("no")) loop=false;
            }
        } while(loop);
    }
}

//自定义的操作符错误异常类
class EOperatorError extends Exception {
    public EOperatorError() {
        super("操作符错误!");
    }
    
    public EOperatorError(String message) {
        super(message);
    }
    
}