String s="ada";
char[] a=s.toCharArray(); 将字符串转换成字符数组

public class test{
    public static void main(String[]args)
    {
        File f =new File("D:d/write.txt");
        Writer writer=null;
        try {
            writer=new FileWriter(f);

        //写法一
        /*String s="adad  afaff哈哈哈";
        char[] ch=s.toCharArray(); //从字符串到字符数组
        writer.write(ch,0,ch.length);
        **write.flush();***/
        //写法二
        /*String s="adad  afaff哈哈哈2";
        writer.write(s,0,s.length()); //因为字符串就是字符数组，所以可以直接使用
        writer.write("addd");   //可实现多次写入
        writer.write("fff");
        **writer.flush();**
        */

        //写法三
        /*writer.append("adad").append("aaa\n"); 
        **writer.flush();***/

    }catch(FileNotFoundException e)
    {
        e.printStackTrace();
    }catch(IOException e)
    {
        e.printStackTrace();
    }finally {
        try {
            if(null!=writer)
            {
                **writer.close();**
            }
        }catch(IOException e)
        {
            e.printStackTrace();
        }
    }
}

}