代码以及解释：

package java2;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

public class Test02 {
    public static void main(String[] args) throws IOException {
        String str = "flag{hello_ctf}";
        //1.封装
        File f=new File("D:\\....test\\资料\\demo.txt");
        //2.输出流,(插入管子),并起一个名字
        FileWriter fw =new FileWriter(f);
        //3.输出
        fw.write(str);
        //4.流关闭
        fw.close();

    }
}