Java程序设计进阶之路三：异常

一、读取文件的步骤：

读取文件操作的每一步都依赖上一步的实现

二、代码分析

1、传统型错误码反馈机制

class errorCodeTypeFile{
			int errorCode = 0;

			if(theFileOpened) {
				determine its size;
				if(gotTheFileLength ){
					allocate that much memory;
					if(gotEnoughMemory){
						read the file into the memory;
						if(readFailed){
							errorCode = -1;
						}
					}
					else {
						errorCode = -2;
					}
				}
				else {
					errorCode = -3;
				}

				close the file;
				if(theFileDidn‘tClose && errorCode == 0){
						errorCode = -4;
			    }
			    else {
			    	errorCode = errorCode and -4;
			    }
		     }
	         else {
		          errorCode = -5;
	         }
	return errorCode;

}

通过反馈的错误码，我们可以了解到哪一步发生错误，但是该种代码可读性差，难以修改，逻辑不清晰。

2、添加异常捕捉机制后的代码

       try {
		open the file;
		determine its size;
		allocate that much memory;
		read the file into the memory;
		close the file;
	} catch (fileOpenFailed ){
		do something;
	} catch (sizeDeterminedFaile){
		do something;
	} catch (memeoryAllocationFailed){
		do something;
	} catch (readFailed){
		do something;
	} catch (fileClosedFailed){
		do something;
	}

代码添加异常捕捉机制后，通过catch后的语句可以了解到异常种类，而且该代码具有可读性高，逻辑分明，通常把try后语句称为业务逻辑代码，catch后语句称为异常处理代码。

三、今日总结