文件的输入输出的应用

1．使用字符输出流将一段文字存入文件，然后使用输入流读取文件中的内容。

public class main {
	public static void main(String[] args) {
		File file = new File("hello.txt");
		String s;
		Scanner r = new Scanner(System.in);
		s = r.nextLine();
		char b[] = s.toCharArray();
		try {
			FileWriter out = new FileWriter(file, true);
			out.write(b);
			out.close();
			FileReader in = new FileReader(file);
			int n = 0;
			while ((n = in.read(b, 0, 2)) != -1) {
				String str = new String(b, 0, n);
				System.out.print(str);
			}
		} catch (IOException e) {
			System.out.println(e);
		}
	}
}

2．将字符串加密后写入文件，然后读取该文件，并解密。

public class Main {
	public static void main(String[] args) {
		File file = new File("hello.txt");
		String s;
		Scanner r = new Scanner(System.in);
		s = r.nextLine();
		char b[] = s.toCharArray();
		for (int i = 0; i < b.length; i++) {
			if (b[i] >= 'x')
				b[i] -= 23;
			else
				b[i] += 3;
		}
		try {
			FileWriter out = new FileWriter(file, true);
			out.write(b);
			out.close();
			FileReader in = new FileReader(file);
			int n = 0;
			while ((n = in.read(b, 0, 1)) != -1) {
				String str = new String(b, 0, n);
				char x[] = str.toCharArray();
				if (x[0] <= 'c')
					System.out.print((char)(x[0] + 23));
				else
					System.out.print((char)(x[0] - 3));
			}
		} catch (IOException e) {
			System.out.println(e);
		}
	}
}