我想追加第一行，但它追加多個數據的最後一行

Question

public class AddMoney { 

    RegisterAndLogin rl = new RegisterAndLogin(); 
    private String UserName; 
    File file; 
    int balance; 
    String sourceamt; 
    Scanner scanner = new Scanner(System.in); 
    String path = "D:\\PesonalAccoutant\\account\\"; 
    String readData; 
    FileWriter fw; 
    BufferedWriter bw; 
    StringBuilder sb; 
    BufferedReader br; 

    public AddMoney(String UserName) { 
     this.UserName = UserName; 
    } 

    public void acceptmoneyvalus() throws IOException { 
     System.out.println("<1> add money to account"); 
     System.out.println("<2> remove money from account"); 
     addmoneytoaccount(); 

    } 

    public void addmoneytoaccount() throws IOException { 
     try { 
      file = new File(path + UserName + ".txt"); 
      fw = new FileWriter(file, true); 
      bw = new BufferedWriter(fw); 
      file.createNewFile(); 
      System.out.println("file create"); 

      if (file.exists()) { 
       br = new BufferedReader(new FileReader(file)); 
       if (file.length() == 0) { 
        System.out.println("reading null data"); 
        bw.write("Balance=" + 0); 
        bw.newLine(); 
        System.out.println("Please enter the amount."); 
        balance = scanner.nextInt(); 
        System.out.println("Please enter source of the ammount"); 
        sourceamt = scanner.next(); 
        addBalance(balance); 
        bw.append("Amount="); 
        bw.append("" + balance); 
        bw.newLine(); 
        bw.append("Source of the amount=" + sourceamt); 
        bw.newLine(); 
        bw.newLine(); 

       } else { 
        System.out.println("else blco"); 
        System.out.println("Please enter the amount."); 
        balance = scanner.nextInt(); 
        System.out.println("Please enter source of the ammount"); 
        sourceamt = scanner.next(); 
        addBalance(balance); 
        bw.append("Amount="); 
        bw.append("" + balance); 
        bw.newLine(); 
        bw.append("Source of the amount=" + sourceamt); 
        bw.newLine(); 
        bw.newLine(); 
       } 
      } else { 
       System.out.println("try to register again..."); 
      } 

     } catch (Exception e) { 
      System.out.println("Error" + e); 
     } finally { 
      bw.close(); 

     } 
    } 

    private void addBalance(int balance) throws IOException { 
     try { 
      int count = 0; 
      br = new BufferedReader(new FileReader(file)); 
      while ((readData = br.readLine()) != null) { 
       count++; 
       sb = new StringBuilder(); 
       if (count == 1) { 

        sb.append(readData); 
        sb.delete(0, 8); 
        System.out.println("full datd is"+readData); 
        // int i=(Integer)sb; 
        int i = Integer.valueOf(sb.toString()); 
        int totalbalance = balance + i; 
        System.out.println("balance is " + sb.toString()); 
        System.out.println("total balnce" + totalbalance); 
        bw.append("Balance=" + totalbalance); 
        bw.newLine(); 
       } 

      } 
     } catch (Exception e) { 

      System.out.println("Error " + e); 
     } finally { 
      br.close(); 
     } 

    } 

} 

我想在第一行添加餘額，但是當我添加更多數據時，它會追加最後兩行而不是文件的開頭。 我希望每一個我加錢時，必須反映在加入量進入

Answer 1

while ((readData = br.readLine()) != null) { 
      count++; 
      sb = new StringBuilder(); 

的while loop在addbalance()方法內部平衡你是instantiating新StringBuilder各一次。

if you wanto append data to the StringBuilder sb;你可以把這個聲明爲 一個實例變量或聲明的變量while循環外這樣

sb = new StringBuilder(); 
while ((readData = br.readLine()) != null) { 
       ++count; 

，並確保更改count++到++count。 因爲你只需要讀你不必去與while loop第一線，你可以只使用readLine();方法

StringBuilder sb = new StringBuilder(); 
private void addBalance(int balance) throws IOException{ 
    readData = br.readLine(); //first line 
    sb.append(readData); 
}