For 循环逻辑运行但没有意义

Question

VisitProcedure.length equals 7

So for some reason this method works how I want it to. But the logic makes no sense to me. I have an array of 7 and i want the user to type in some part of the index 0-6 and it will display the value at that index. If they type in a number thats out of bounds then it throws an exception. But this is how i read the if statement logic

if index is less then 0 or index is greater then 6 do this (p = VisitProcedure[index].getProcedure(); //displays the index

But instead it does the opposite. When i pick 0-6 It displays the value of the array at that index. And when i do anything else its out of index. Also when i try a different logic

if index is greater then equal to 0 and less then 7 do this

I still run into error. But basically everything works fine it just doesnt make sense to me why.

public Procedure GetByIndex(int index)throws ArrayIndexOutOfBoundsException {
            Procedure p;
            if (index < 0 || index > 1 - VisitProcedure.length) { //switching 1 - to - 1 still doesnt work
                p = VisitProcedure[index].getProcedure();
                return p;   
            }
            else{
                ArrayIndexOutOfBoundsException ar;
                ar = new ArrayIndexOutOfBoundsException(); 
                throw ar;
                //throw new ArrayIndexOutOfBoundsException();

            }
        }

Answer 1

Your current code is wrong, but it works anyway for the following reasons:

• if you pass a valid index (between 0 and 6), index > 1 - VisitProcedure.length is true (since 1 - VisitProcedure.length is negative), so the if condition is true and you return VisitProcedure[index].getProcedure() .

• If you pass an invalid index > 6 or index < 0 , the condition is still true , and accessing an invalid index of the array throws ArrayIndexOutOfBoundsException (ie it is still thrown, but not by the else clause).

In other words, your condition is always true , so your code is equivalent to:

public Procedure GetByIndex(int index)throws ArrayIndexOutOfBoundsException {
    return VisitProcedure[index].getProcedure();
}

Answer 2

If(index>0 && index<=VisitProcedure.length-1){
    //if index is greater than 0 and less than or equal to index 6

    p = VisitProcedure[index].getProcedure();
            return p; 

}else{
 ArrayIndexOutOfBoundsException ar;
            ar = new ArrayIndexOutOfBoundsException(); 
            throw ar;
            //throw new ArrayIndexOutOfBoundsException();

}