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块.但是,我无法在try-catch块之外获取变量.

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..");
    }


}
}

但以下不起作用.

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 );
}
}

尝试了以下内容

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 );

}
}

但错误说 The local variable num may not have been initialized

我怎样才能摆脱这个错误？

Answer 1

你应该在try块之前声明变量(为了使它在try-catch块之后仍然在范围内),但是给它一个初始值:

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 );

  }
}