Replace Magic Number with Symbolic Constants - 매직넘버 심볼릭 상수 치환

문제점

매직넘버를 사용합니다.

매직넘버란 무엇인가 살펴보자면 아래와 같은 코드를 사용하고 있습니다.

if (100 < input.length())

이렇게 되었을 경우 문제점은

1. 의미를 이해하기 어렵습니다.

2. 복수의 장소에서 사용된다면 변경하기 힘듭니다.

해결책

상수를 사용하면 됩니다.

public static final int MAX_INPUT_LENGTH = 100;

연습문제 

문제

public class Robot {
    private final String name;

    public Robot(String name) {
        this.name = name;
    }

    public void order(int command) {
        if (command == 0) {
            System.out.println(name + " walks.");
        } else if (command == 1) {
            System.out.println(name + " stops.");
        } else if (command == 2) {
            System.out.println(name + " jumps.");
        } else {
            throw new IllegalArgumentException("Command error. command = " + command);
        }
    }

    public static void main(String[] args) {
        Robot robot = new Robot("Andrew");
        robot.order(0);
        robot.order(1);
        robot.order(2);
    }
}

상수로 해결해보자.

public class Robot {
    private static final int COMMAND_WALK = 0;
    private static final int COMMAND_STOP = 1;
    private static final int COMMAND_JUMP = 2;
    
    private final String name;

    public Robot(String name) {
        this.name = name;
    }

    public void order(int command) {
        if (command == COMMAND_WALK) {
            System.out.println(name + " walks.");
        } else if (command == COMMAND_STOP) {
            System.out.println(name + " stops.");
        } else if (command == COMMAND_JUMP) {
            System.out.println(name + " jumps.");
        } else {
            throw new IllegalArgumentException("Command error. command = " + command);
        }
    }

    public static void main(String[] args) {
        Robot robot = new Robot("Andrew");
        robot.order(COMMAND_WALK);
        robot.order(COMMAND_STOP);
        robot.order(COMMAND_JUMP);
    }
}

Enum으로 해결해보자.

public class Robot {
    private enum Command {
        WALK, STOP, JUMP
    }
    private final String name;

    public Robot(String name) {
        this.name = name;
    }

    public void order(Command command) {
        if (command == Command.WALK) {
            System.out.println(name + " walks.");
        } else if (command == Command.STOP) {
            System.out.println(name + " stops.");
        } else if (command == Command.JUMP) {
            System.out.println(name + " jumps.");
        } else {
            throw new IllegalArgumentException("Command error. command = " + command);
        }
    }

    public static void main(String[] args) {
        Robot robot = new Robot("Andrew");
        robot.order(Command.WALK);
        robot.order(Command.STOP);
        robot.order(Command.JUMP);
    }
}