期望：用戶輸入自己的名字後進行游戲, 游戲完成後會得到一個double類型的分數, 然後把名字和分數寫入txt檔，最後讀取txt檔的資料使用arraylist對分數進行排名，然後輸出.

目前的進度是這樣的

public class abc{
	private String usersname;
	private double scores;



	public String getusername() {
		return usersname;
	}
	public void setusername(String usersname) {
		this.usersname = usersname;
	}
	public double getscore() {
		return scores;
	}
	public void setscore(double scores) {
		this.scores = scores;
	}
	public abc(){
		
	}
	
	public abc(String username,double score){
		usersname = username;
		scores = score;
	}
}

import java.io.*;


public class rw_txt {
    public static void main(String[] args) throws IOException {
    	abc s = new abc();
    	
    	
 
        File fw = new File("a.txt");
        FileOutputStream fop = new FileOutputStream(fw,true);
 
        OutputStreamWriter writer = new OutputStreamWriter(fop, "UTF-8");

        writer.append(s.getusername());
 
        writer.append("\t");
        
        writer.append(s.getscore());  <---此處報錯
        
        writer.close();
 
        fop.close();
        
        FileInputStream fip = new FileInputStream("a.txt");
        InputStreamReader reader = new InputStreamReader(fip, "UTF-8");
        

        StringBuffer sb = new StringBuffer();
        while (reader.ready()) {
        	sb.append((char)reader.read());
        }
        System.out.println(sb.toString());
        reader.close();
        fip.close();
    }

}

望大神請教TvT 小的剛學java沒多久,腦袋實在轉不過來了