7.2文件输入输出 File对象封装了文件或路径的属性，但是它既 不创建文件，也不读写文件数据。 ■为了完成VO操作，需要使用恰当的Java I/O类 创建对象。 "本节介绍Scanner和PrintWriter类读写文件
7.2 文件输入输出 ◼ File对象封装了文件或路径的属性，但是它既 不创建文件，也不读写文件数据。 ◼ 为了完成I/O操作，需要使用恰当的Java I/O类 创建对象。 ◼ 本节介绍Scanner和PrintWriter类读写文件。 13
PrintWriter类 iava.io.PrintWritera类可用来创建一个文件并向文 本文件写入数据。 File file=new File("c:\la.txt"); PrintWriter output new PrintWriter(file); 如果文件不存在，则创建一个新文件
14 PrintWriter类 java.io.PrintWriter类可用来创建一个文件并向文 本文件写入数据。 如果文件不存在，则创建一个新文件。 File file = new File(“c:\\a.txt"); PrintWriter output = new PrintWriter(file);
使用PrintWriter类写数据 java.io.PrintWriter +PrintWriter(filename:String) 为特定的文件对象创建一个PrintWriter>对象 +print(s:String):void Writes a string. +print(c:char):void Writes a character. +print(cArray:char[]):void Writes an array of character. +print(i:int):void 输出一个整数。 +print(1:long):void Writes a long value. +print(f:float):void Writes a float value. +print(d:double):void Writes a double value. +print(b:boolean):void Writes a boolean value. Also contains the overloaded A println method acts like a print method;additionally it println methods. prints a line separator.The line separator string is defined Also contains the overloaded by the system.It is Ir'n on Windows and \n on Unix. printf methods. The printf method was introduced in§3.6，“Formatting Console Output and Strings
15 使用 PrintWriter 类写数据 java.io.PrintWriter +PrintWriter(filename: String) +print(s: String): void +print(c: char): void +print(cArray: char[]): void +print(i: int): void +print(l: long): void +print(f: float): void +print(d: double): void +print(b: boolean): void Also contains the overloaded println methods. Also contains the overloaded printf methods. . Creates a PrintWriter for the specified file. Writes a string. Writes a character. Writes an array of character. Writes an int value. Writes a long value. Writes a float value. Writes a double value. Writes a boolean value. A println method acts like a print method; additionally it prints a line separator. The line separator string is defined by the system. It is \r\n on Windows and \n on Unix. The printf method was introduced in §3.6, “Formatting Console Output and Strings.” 为特定的文件对象创建一个PrintWriter对象 输出一个整数
PrintWriter类的方法 void vrite(char[]buf) 写入字符数组。 void rite(char[]buf,int off,int len) 写入字符数组的某一部分。 void 夏rite(int c) 写入单个字符。 void write(String s) 写入字符串。 void ■rite(String s, int off,int len) 写入字符串的某一部分
PrintWriter 类的方法
public PrintWriter(File file) throws FileNotFoundException ■抛出： ▣FileNotFoundException-如果在打开或创建文件时 发生其他一些错误
public PrintWriter(File file) throws FileNotFoundException ◼ 抛出： ❑ FileNotFoundException - 如果在打开或创建文件时 发生其他一些错误