file的知识

String str = null;
String s1 = "";
try {
File f = new File("D:\xxx.txt");
if (f.exists()) {
System.out.print("文件存在");
} else {
System.out.print("文件不存在");
f.createNewFile();// 不存在则创建
}
BufferedReader input = new BufferedReader(System.in);

while ((str = input.readLine()) != null) {
s1 += str + "\n";
}
System.out.println(s1);
input.close();
s1 += content;

BufferedWriter output = new BufferedWriter(new FileWriter(f));
output.write(s1);
output.close();
} catch (Exception e) {
e.printStackTrace();

}