Custom Exception类每次显示Unreachable catch块 [英] Custom Exception class shows Unreachable catch block everytime

问题描述

  public class MyException extends Exception { 
 private static final long serialVersionUID = -2151515147355511072L; 
 private String message = null; 
 
 public MyException（）{
 super（）; 
} 
 
 public MyException（String message）{
 super（message）; 
 this.message = message; 
} 
 
 public MyException（Throwable cause）{
 super（cause）; 
} 
 
 @Override 
 public String toString（）{
 return message; 
} 
 
 @Override 
 public String getMessage（）{
 return message; 
} 
} 
  

但是当我尝试使用这个类时，如下所示，它给出编译时错误。

  try {
 System.out.println（this）; 
} catch（MyException e）{
 // TODO：handle exception 
} 
  

编译时间错误：

  MyException无法访问的catch块。我的问题是如果我正在扩展Exception class& amp; ;在所有构造函数中调用super，那么为什么会发生这个错误？
解决方案
显然，你没有做任何会生成一个 MyException 。首先写一个带有签名的方法抛出MyException ，调用它，然后你的问题解决了。这是一个例子：
  public void someMethod（）throws MyException 
 {
 // some condition here 。 
 // if met .. 
 throw new MyException（cause）; 
} 
  
，并将您的主要代码修改为：
  try {
 someMethod（）; 
 System.out.println（this）; 
} catch（MyException e）{
 // TODO：handle exception 
} 
  
 
I've created a custom Exception class that I want to use in my application:
public class MyException extends Exception {
    private static final long serialVersionUID = -2151515147355511072L;
    private String message = null;

    public MyException() {
        super();
    }

    public MyException(String message) {
        super(message);
        this.message = message;
    }

    public MyException(Throwable cause) {
        super(cause);
    }

    @Override
    public String toString() {
        return message;
    }

    @Override
    public String getMessage() {
        return message;
    }
}
But when I try to use this class, like below, it gives a compile time error.
try {
    System.out.println("this");
} catch (MyException  e) {
    // TODO: handle exception
}
Compile time error:
Unreachable catch block for MyException . This exception is never thrown from the try statement body
My question is if I'm extending Exception class & calling super in all constructors, then why this error is occurring?
解决方案
Obviously, you are not doing anything that'd generate a MyException. First write a method with the signature throws MyException, call it and then your problem is solved. Here is an example:
public void someMethod()throws MyException
{
    //some condition here.
    //if met..
    throw new MyException("cause");
}
and modify your main code as:
try {
    someMethod();
    System.out.println("this");
} catch (MyException  e) {
    // TODO: handle exception
}


                        
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