Java 如何访问 try-catch 块之外的变量

Question

我是 java 的初学者，正在玩 try-catch block.However，我无法获取 try-catch 块之外的变量。

以下代码有效。

class factorial{
public static void main(String[] args){
    try {
         int num = Integer.parseInt(args[0]);
         System.out.println(num );
    }
    catch(Exception e){
        System.out.println(e+" Cannot convert arg to int, exiting..");
    }


}
}

但是下面的不行。

class factorial{
public static void main(String[] args){
    try {
         int num = Integer.parseInt(args[0]);
    }
    catch(Exception e){
        System.out.println(e+" Cannot convert arg to int, exiting..");
    }
     System.out.println(num );
}
}

也尝试了以下方法

class factorial{
public static void main(String[] args){
    int num;
    try {
         num = Integer.parseInt(args[0]);
    }
    catch(Exception e){
        System.out.println(e+" Cannot convert arg to int, exiting..");
    }
     System.out.println(num );

}
}

但错误显示 The local variable num may not have been initialized

我怎样才能摆脱这个错误？

Answer 1

您应该在 try 块之前声明变量（以便它在 try-catch 块之后仍然在范围内），但给它一个初始值：

class factorial{
  public static void main(String[] args){
    int num = 0;
    try {
         num = Integer.parseInt(args[0]);
    }
    catch(Exception e){
        System.out.println(e+" Cannot convert arg to int, exiting..");
    }
    System.out.println(num );

  }
}

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