程式碼中的魔術數字

原本以為很多文章都會提到，沒想到稍微google一下中文資訊居然這麼少，既然自己的文章提到了，那就自己說明一下吧。





通常在程式碼中為了保持彈性，某些狀態會設定為數字當作彼此溝通的介面，這邊就舉例最常遇到的http狀態碼來說明，200表示成功，這個很常遇到，所以可能不用查也知道意思，但其他的數字呢?如果用變數的方式來取代是否可以立馬增加可讀性呢?

以下邊的變數名稱為例，如果今天要判斷連線是否成功 response.code == 200還是response.code == HttpStatus.SC_OK可讀性比較高呢？數字對於人類來說沒有可讀性，文字才有，如果只是用數字代表某個意思，就非得看更多的程式，理解上下文做了什麼之後，我們才能知道某個數字到底代表著什麼意思，但今天如果是清楚的模組與命名，我們就能夠一看就懂，這就是增加程式可讀性的小細節。

	package org.apache.http;
	public interface HttpStatus {
	int SC_ACCEPTED = 202;
	int SC_BAD_GATEWAY = 502;
	int SC_BAD_REQUEST = 400;
	int SC_CONFLICT = 409;
	int SC_CONTINUE = 100;
	int SC_CREATED = 201;
	int SC_EXPECTATION_FAILED = 417;
	int SC_FAILED_DEPENDENCY = 424;
	int SC_FORBIDDEN = 403;
	int SC_GATEWAY_TIMEOUT = 504;
	int SC_GONE = 410;
	int SC_HTTP_VERSION_NOT_SUPPORTED = 505;
	int SC_INSUFFICIENT_SPACE_ON_RESOURCE = 419;
	int SC_INSUFFICIENT_STORAGE = 507;
	int SC_INTERNAL_SERVER_ERROR = 500;
	int SC_LENGTH_REQUIRED = 411;
	int SC_LOCKED = 423;
	int SC_METHOD_FAILURE = 420;
	int SC_METHOD_NOT_ALLOWED = 405;
	int SC_MOVED_PERMANENTLY = 301;
	int SC_MOVED_TEMPORARILY = 302;
	int SC_MULTIPLE_CHOICES = 300;
	int SC_MULTI_STATUS = 207;
	int SC_NON_AUTHORITATIVE_INFORMATION = 203;
	int SC_NOT_ACCEPTABLE = 406;
	int SC_NOT_FOUND = 404;
	int SC_NOT_IMPLEMENTED = 501;
	int SC_NOT_MODIFIED = 304;
	int SC_NO_CONTENT = 204;
	int SC_OK = 200;
	int SC_PARTIAL_CONTENT = 206;
	int SC_PAYMENT_REQUIRED = 402;
	int SC_PRECONDITION_FAILED = 412;
	int SC_PROCESSING = 102;
	int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
	int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
	int SC_REQUEST_TIMEOUT = 408;
	int SC_REQUEST_TOO_LONG = 413;
	int SC_REQUEST_URI_TOO_LONG = 414;
	int SC_RESET_CONTENT = 205;
	int SC_SEE_OTHER = 303;
	int SC_SERVICE_UNAVAILABLE = 503;
	int SC_SWITCHING_PROTOCOLS = 101;
	int SC_TEMPORARY_REDIRECT = 307;
	int SC_UNAUTHORIZED = 401;
	int SC_UNPROCESSABLE_ENTITY = 422;
	int SC_UNSUPPORTED_MEDIA_TYPE = 415;
	int SC_USE_PROXY = 305;
	}

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