java - 命令行参数

Question

 public static void main(String[] args) {

    if (args.length == 0) { //If nothing is typed into the command line, the message below is printed
        System.out.println("(!)You have not entered anything in the commandline.");
    }else if (args.length > 0){
        try {
            Integer x = new Integer(0);
            if (x<=0){
                System.out.println("(!)You may not have a negative number in the command line.");
            }
            x = Integer.parseInt(args[0]);
        } catch (NumberFormatException y) {
            System.out.println("(!)Your entry in the commandline must be an integer.");
            System.exit(1);
        }
    }
}

在上面的代码中，我尝试在命令行中输入一个正数，但它一直在运行我的 println: "(!)You may not have a negative number"即使 x(我在命令行中输入的内容)不是<= 0。我感觉我忘了添加一些东西。

Answer 1

 Integer x = new Integer(0);
            if (x<=0){
                System.out.println("(!)You may not have a negative number in the command line.");
            }
            x = Integer.parseInt(args[0]);

在这里您还可以期待什么，您正在用零初始化并立即检查 if 条件。

您必须首先将 arg[0] 解析为整数，然后再进行逻辑处理

你必须写

 Integer  x = Integer.parseInt(args[0]);
            if (x<=0){
                System.out.println("(!)You may not have a negative number in the command line.");
            }