“如果（int == 1）”不起作用

Question

So I am trying to learn Java, and have been writing a basic program based off of the 21 matches game; in which each player takes turns taking 1,2 or 3 matches. The player to take the last match loses.

It was going well until I found that when the user was about to win, the program wouldn't enter the final else if statement; it would skip over it and come back to the user, without the computer having taken any matches. Attached is the method I have written for the computers turn.

public static int ComputerPlays(int matches){ //Method for the computers turn
    int matchesTaken = 0;

    if (matches > 7){ matchesTaken = new Random().nextInt(3)+1; }
    else if (matches > 4 && matches < 8){ matchesTaken = matches - 4; }
    else if (matches < 5){ matchesTaken = matches - 1; }
    else if (matches == 1){ matchesTaken = 1; }

    System.out.println("Computer takes " + matchesTaken + " matches");
    return(matches - matchesTaken);
}

The line else if (matches == 1){ matchesTaken = 1; } else if (matches == 1){ matchesTaken = 1; } is where I'm having a problem. Any help would be appreciated.

PS I realize that I could turn the else if into an else statement, but the main thing is I want to learn what the problem is, not just get around it.

Answer 1

You should move the (matches == 1) before (matches < 5) condition. The code is not reachable till (matches == 1) as this condition is satisfied by (matches < 5) also.

Updated code:

public static int ComputerPlays(int matches){ //Method for the computers turn
    int matchesTaken = 0;

    if (matches > 7){ matchesTaken = new Random().nextInt(3)+1; }
    else if (matches > 4 && matches < 8){ matchesTaken = matches - 4; }
    else if (matches == 1){ matchesTaken = 1; }
    else if (matches < 5){ matchesTaken = matches - 1; }

    System.out.println("Computer takes " + matchesTaken + " matches");
    return(matches - matchesTaken);
}

Answer 2

the matches < 5 will Always be reached Before the matches == 1 meaning it will never trigger the second if. so either you change order of the if's or add a Another argument to your less than 5 ie (matches < 5 && matches > 1).

Answer 3

The condition (matches == 1) will be unreachable since your previous condtion is always makes your later condition true ie., if (matches < 5) which actually considers matches == 1 . You can make the last two condition as:

else if (matches < 5 && matches != 1){ matchesTaken = matches - 1; }
    else if (matches == 1){ matchesTaken = 1; }

or like

else if (matches < 5 && matches > 1){ matchesTaken = matches - 1; }
    else if (matches == 1){ matchesTaken = 1; }

Answer 4

Your problem is that the statement

else if (matches < 5){ matchesTaken = matches - 1; }

will be true when the matches is 1. Thus the else if will never be entered. You can change it to

else if (matches < 5 && matches != 1){ matchesTaken = matches - 1; }

That way, it will not trigger when the number of matches is 1 and the following block can execute successfully.

Answer 5

Put

else if (matches == 1){ matchesTaken = 1; }

before

else if (matches < 5){ matchesTaken = matches - 1; }

The order is important. In IF_ELSE, once a match is occurs it doesn't check the next condition. In your case as matches<5 is true it won't check matches==1 .

Answer 6

You've already checked else if (matches < 5) then it's useless checking
else if (matches == 1) , because above condition will end the if chain. So you can change else if (matches < 5) to else if (matches < 5 && matches !=1) to make the last statement also reachable.

Answer 7

When ever you use else if, use equal conditions (==) first then go for greater than or equal (X>=Y) or less than or equal(X<=Y) conditions.

The statement which satisfies the condition first will execute and rest of else if statements will ignore.

Happy Coding!

Answer 8

if (matches > 7){ matchesTaken = new Random().nextInt(3)+1; }
else if (matches > 4 && matches < 8){ matchesTaken = matches - 4; }
else if (matches < 5){ matchesTaken = matches - 1; }
else if (matches == 1){ matchesTaken = 1; }

In your code first execute else if (matches < 5){ matchesTaken = matches - 1; } else if (matches < 5){ matchesTaken = matches - 1; }

This line execute first and this line also satisfy if matches == 1 , thats why it will never goes to the next line ( else if (matches == 1){ matchesTaken = 1; } ) when matches == 1

Answer 9

1 is less than 5. This means that when matches is equal to one, it will always be captured in the statement "else if (matches < 5){ matchesTaken = matches - 1; }".

This is the reason why (matches == 1) is never executed.