java小白——try-catch语句中的while循环问题

今天药忘吃喽~ 2023-06-19 09:57 145阅读 0赞

## 无限循环问题 ##

**在今天的课堂练习中，我想实现在try-catch语句中实现循环输入，  
即为当输入错误时，捕获异常输出，且可以重新输入。**

**第一次编写的代码：**（此代码存在bug）

package 异常;
    
    import java.io.Console;
    import java.util.Scanner;
    
    import javax.management.RuntimeErrorException;
    
    public class Test4 {
        
    	public static double avg(double x,int y){
        
    		double avg = 0;
    		if (y==0) {
        
    			throw new RuntimeException("除数不能为0！");
    			}
    		else{
        
    		      avg = x/y;
    		}
    		     return avg;	
    	}
    
    	public static void main(String[] args) {
        
    		
    		Scanner scanner = new Scanner(System.in);
    		while(true){
        
    
    		try {
        		
    			System.out.println("请输入总成绩：");
    			double x = scanner.nextDouble();
    			System.out.println("请输入总人数：");
    			int y = scanner.nextInt();
    			double avg = avg(x, y);
    			System.out.println("平均成绩为："+avg);		
    		} 
    		catch (RuntimeException e) {
        
    			System.out.println(e.getMessage());
    			continue;
    		}
    		catch (Exception e) {
        
    			System.out.println("请输入数字！");
    			continue;
    		}
    		finally {
        
    			scanner.close();			
    		}	
    		break;
    		
    		}
    	}
    
    }

**运行结果：**  
出现了无限循环  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTE3NDIwOA_size_16_color_FFFFFF_t_70]

## 解决方法 ##

**bug原因**

*  当输入异常时，捕捉到异常Exception，开始下一次的循环，但是此时数据缓冲区依旧留有我上次输入的异常数据，并没有清除这些数据，这时就又开始捕捉异常Exception，还是错误，于是这个异常一直被捕捉一直被输出。出现了无限循环的bug。  
    那么解决的方法就是将捕捉到的异常Exception数据去清除。

**方案一：在catch()语句之中加上scanner.next();**  
**代码如下：**

package 异常;
    
    import java.io.Console;
    import java.util.Scanner;
    
    import javax.management.RuntimeErrorException;
    
    public class Test4 {
        
    	public static double avg(double x,int y){
        
    		double avg = 0;
    		if (y==0) {
        
    			throw new RuntimeException("除数不能为0！");
    			}
    		else{
        
    		      avg = x/y;
    		}
    		     return avg;	
    	}
    
    	public static void main(String[] args) {
        
    		
    		Scanner scanner = new Scanner(System.in);
    		while(true){
        
    		try {
        		
    			System.out.println("请输入总成绩：");
    			double x = scanner.nextDouble();
    			System.out.println("请输入总人数：");
    			int y = scanner.nextInt();
    			double avg = avg(x, y);
    			System.out.println("平均成绩为："+avg);		
    		} 
    		catch (RuntimeException e) {
        
    			System.out.println(e.getMessage());
    			scanner.next();
    		}
    		catch (Exception e) {
        
    			System.out.println("请输入数字！");
    			scanner.next();
    		}			
    		}
    	}
    
    }

**![运行结果][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTE3NDIwOA_size_16_color_FFFFFF_t_70 1]**  
**成功结束循环**

**方案二：将Scanner的对象scanner写在try语句之中**  
**代码如下：**

package 异常;
    
    import java.io.Console;
    import java.util.Scanner;
    
    import javax.management.RuntimeErrorException;
    
    public class Test4 {
        
    	public static double avg(double x,int y){
        
    		double avg = 0;
    		if (y==0) {
        
    			throw new RuntimeException("除数不能为0！");
    			}
    		else{
        
    		      avg = x/y;
    		}
    		     return avg;	
    	}
    
    	public static void main(String[] args) {
        
    		
    		
    		while(true){
        
    		try {
        	
    			Scanner scanner = new Scanner(System.in);
    			System.out.println("请输入总成绩：");
    			double x = scanner.nextDouble();
    			System.out.println("请输入总人数：");
    			int y = scanner.nextInt();
    			double avg = avg(x, y);
    			System.out.println("平均成绩为："+avg);		
    		} 
    		catch (RuntimeException e) {
        
    			System.out.println(e.getMessage());
    		}
    		catch (Exception e) {
        
    			System.out.println("请输入数字！");
    		}			
    		}
    	}
    
    }

**运行结果：**  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80NTE3NDIwOA_size_16_color_FFFFFF_t_70 2]  
**成功结束循环！**

## ps： ##

**try-catch语句一次只能捕获一个异常**

\*\***捕获或异常为null(Caught Throwable or Exception is null)  
此bug请详情看此文章（http://www.it1352.com/619288.html）在此不进行解释**  
此文章可能有诸多纰漏，如有问题欢迎提出，并在此感谢网上诸位大神的解决方案,本人只是进行一个个人的汇总。

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