無法將arraylist保存到文件中

Question

我有以下代碼，我從main調用。 代碼有問題，它將產品保存如下：1，ipad，499.0，ELECTRONICS

1，ipad，499.0，ELECTRONICS 2，Java Ebook，19.99，BOOK

我不明白第一個來自哪里。 能否請你提供一些指示。

非常感謝...

public void saveProductsToDisk() {

    String filename = "/Users/paddy/UCSC/Workspace/productDB/src/productdb/savedProducts.csv";
    BufferedWriter output = null;
    try 
    {
        output =  new BufferedWriter(new FileWriter(filename));
        StringBuffer line = new StringBuffer();
        for (Product p: getAllProducts())
        {
            line.append(p.getId() <=0 ? "" : p.getId());
            line.append(CSV_SEPARATOR);
            line.append(p.getName().trim().length() == 0? "" : p.getName());
            line.append(CSV_SEPARATOR);
            line.append(p.getPrice() < 0 ? "" : p.getPrice());
            line.append(CSV_SEPARATOR);
            line.append(p.getDept().toString());
            line.append("\n");
            output.write(line.toString());
        }
        output.flush();
        output.close();
    }
    catch (IOException ex)
    {
        System.out.println("IO error for " + filename +
                ": " + ex.getMessage());
    }
}

Answer 1

您在for循環的每次迭代中重復使用相同的line變量。

嘗試重新初始化for循環頂部的line ，如下所示：

...
StringBuilder line;
for (Product p: getAllProducts()) {
  line = new StringBuilder();
  line.append(p.getId() <=0 ? "" : p.getId());
  ...

Answer 2

用這個：

public void saveProductsToDisk() {

    String filename = 

"/Users/paddy/UCSC/Workspace/productDB/src/productdb/savedProducts.csv";
    BufferedWriter output = null;
    try 
    {
        output =  new BufferedWriter(new FileWriter(filename));
        StringBuilder line = null;
        for (Product p: getAllProducts())
        {
            line = new StringBuilder();
            line.append(p.getId() <=0 ? "" : p.getId());
            line.append(CSV_SEPARATOR);
            line.append(p.getName().trim().length() == 0? "" : p.getName());
            line.append(CSV_SEPARATOR);
            line.append(p.getPrice() < 0 ? "" : p.getPrice());
            line.append(CSV_SEPARATOR);
            line.append(p.getDept().toString());
            line.append("\n");
            output.write(line.toString());
        }
        output.flush();
        output.close();
    }
    catch (IOException ex)
    {
        System.out.println("IO error for " + filename +
                ": " + ex.getMessage());
    }
}