Java Fundamentals Enhanced IO Flow Note 55:io Flow exercise custom class simulation LineNumberReader get line number function case

1. Get line number function case for custom class simulation LineNumberReader

2. Code implementation:

(1)Mybufferedreader. Java:

1  Packagecn.itcast_08;2 3 Importjava.io.IOException;4 ImportJava.io.Reader;5 6 /*7 * Simulate BufferedReader's readline () function with reader8  * 9 * ReadLine (): reads one line at a time, determines whether to end with newline characters, returns only content, and does not return newline charactersTen  */ One  Public classMybufferedreader { A     PrivateReader R; -  -      PublicMybufferedreader (Reader r) { the          This. R =R; -     } -  -     /* + * Think: Write a method, the return value is a string.  -      */ +      PublicString ReadLine ()throwsIOException { A         /* at * I'm going to return a string, what do I do? We have to see what the R object can read. Two read methods, one character at a time, or one character array at a time - * So, we are going to return a string, which method is better? It's easy to think of a better character array, but the question is, how long is the array length ? - * There is no way to define the length of the array, you define how long is not appropriate. Therefore, you can only choose to read one character at a time.  - * But, in this way, when we read down a character again, the last character is lost so we should define a temporary storage space to store the read characters.  - * Who does this compare with? Array, collection, string buffer Three are available to choose from.  - * After a simple analysis, the final choice is to use a string buffer object. And it's StringBuilder. in          */ -StringBuilder SB =NewStringBuilder (); to  +         //The most troublesome thing to do with this reading is the end of judgment, but it should be read until the end of the 1 -          the          *         /* $ HelloPanax Notoginseng  World - Java the          + 104101108108111 A 119111114108100 the 1069711897 +          */ -          $         intCH = 0; $          while(ch = r.read ())! =-1) {//104,101,108,108,111 -             if(ch = = ' \ r ')) { -                 Continue; the             } - Wuyi             if(ch = = ' \ n ') { the                 returnSb.tostring ();//Hello -}Else { WuSb.append ((Char) ch);//Hello -             } About         } $  -         //to prevent data loss, determine the length of SB cannot be greater than 0 -         if(Sb.length () > 0) { -             returnsb.tostring (); A         } +  the         return NULL; -     } $  the     /* the * Write a closing method first the      */ the      Public voidClose ()throwsIOException { -          This. R.close (); in     } the}

(2)MyLineNumberReader2. Java:

1  Packagecn.itcast_09;2 3 Importjava.io.IOException;4 ImportJava.io.Reader;5 6 ImportCn.itcast_08.MyBufferedReader;7 8  Public classMyLineNumberReader2extendsMybufferedreader {9     PrivateReader R;Ten  One     Private intlinenumber = 0; A  -      PublicMyLineNumberReader2 (Reader r) { -         Super(r); the     } -  -      Public intGetlinenumber () { -         returnlinenumber; +     } -  +      Public voidSetlinenumber (intlinenumber) { A          This. linenumber =linenumber; at     } -  - @Override -      PublicString ReadLine ()throwsIOException { -linenumber++; -         return Super. ReadLine (); in     } -}

(3) test class Mylinenumberreadertest, as follows:

1  Packagecn.itcast_09;2 3 ImportJava.io.FileReader;4 Importjava.io.IOException;5 6  Public classMylinenumberreadertest {7      Public Static voidMain (string[] args)throwsIOException {8         //Mylinenumberreader MLNR = new Mylinenumberreader (New FileReader (9         //"My.txt"));Ten  OneMyLineNumberReader2 MLNR =NewMyLineNumberReader2 (NewFileReader ( A"My.txt")); -  -         //Mlnr.setlinenumber (ten); the  -         //System.out.println (Mlnr.getlinenumber ()); -         //System.out.println (Mlnr.getlinenumber ()); -         //System.out.println (Mlnr.getlinenumber ()); +  -String line =NULL; +          while(line = Mlnr.readline ())! =NULL) { ASystem.out.println (Mlnr.getlinenumber () + ":" +Line ); at         } -  - mlnr.close (); -     } -}

Run the effect as follows:

Java Fundamentals Enhanced IO Flow Note 55:io Flow exercise custom class simulation LineNumberReader get line number function case