流的append

StringBuffer的引用
 1 public static void main(String[] args) throws IOException {

        File file = new File("a.txt");

        Reader reader = new FileReader(file);

        System.out.println((char) reader.read());

        char[] cbuf = new char[5];
        reader.read(cbuf);
        System.out.println(new String(cbuf));

        char[] chars = new char[1024];
        int len = -1;
        StringBuffer stringBuffer = new StringBuffer();
        while ((len = reader.read(chars)) != -1) {
            stringBuffer.append(chars, 0, len);

        }

        System.out.println(stringBuffer.toString());

        reader.close();

    }

调用方法的参数追加

public class CopeText {
    public static void main(String[] args) throws IOException {
        cope();
    }
    
    private static void cope() throws IOException {
        FileReader fr=new FileReader("a.txt");
        FileWriter fw=new FileWriter("b.txt",true);
        char[] buff=new char[1024];
        int len=-1;
        if((len=fr.read(buff))!=-1){
            
            fw.write(buff,0,len);
        }
        fw.close();
        fr.close();
    }
}