为什么会抛出异常？

Question

I am preparing for OCA exams and read a lot, so today I saw an a question. Here is a code:

public class Fork {
  public static void main(String[] args) {
    if (args.length == 1 | args[1].equals("test")) {
        System.out.println("Test case");
    } else {
        System.out.println("production " + args[0]);
    }
  }     
}

And the command-line invocation:

java Fork live2

I thought that answer would be "production java" but the answer is "An exception is thrown at runtime" . Why is that? we are providing values for args right? Can some one please explain me what is going on? Thanks!

Answer 1

In java Fork live2 there's only 1 command line argument - live2 .

args.length == 1 | args[1].equals("test") args.length == 1 | args[1].equals("test") is an OR operator that doesn't short circuit, which means both operands are guaranteed to be evaluated ( || is the OR operator that short circuits and only evaluates the right operand if the left operand is false), so if you supply a single command line argument as you did in java Fork live2 , args[1].equals("test") would still be evaluated and throw an ArrayIndexOutOfBoundsException exception.

If you change your condition to

if (args.length == 1 || args[1].equals("test"))

you'll get Test case printed, since args.length == 1 would be true and args[1].equals("test") won't be evaluated.

Answer 2

in your if statement:

args[1].equals("test")

you have only one argument, so args[1] throw array out of bound

Answer 3

Instead of using | , use || and instead of using args[1].equals("test") use args[0].equals("test") .

In the end it should look something like this:

public class Fork {
  public static void main(String[] args) {
    if (args.length == 1 || args[0].equals("test")) {
        System.out.println("Test case");
    } else {
        System.out.println("production " + args[0]);
    }
  }     
}

Answer 4

You are giving only one command line argument. So while checking for args 1 , you are getting ArrayIndexOutOfBound Exception.. If you give two arguments, it will work perfectly..