问题
I am writing a kind of a cash machine program that will output the data into a file (Yes, I know its not in English, but that's not the point) and I am experiencing an error.
When I try to use PrintWriter
it doesn't work, I don't know why.
public void writeFooter(List<Purchase> list) throws Exception{
int amountSold = 0;
int amountNotSold = 0;
int moneyRecieved = 0;
openStreams();
printer.println("Проданные товары: ");
for(int i = 0; i <= list.size() - 1;i++){
if(list.get(i).isSold()){
writeToFile(list.get(i), dir);
amountSold++;
moneyRecieved += list.get(i).getPrice();
}
}
printer.println();
printer.println("Не проданные товары: ");
for(int i = 0; i <= list.size() - 1; i ++){
if(!list.get(i).isSold()){
writeToFile(list.get(i), dir);
amountNotSold++;
}
}
printer.println();
printer.println("Всего: "+list.size());
printer.println("Кол-во проданно: "+ amountSold);
printer.println("Кол-во не проданно: "+ amountNotSold);
printer.println("Выручка: "+ moneyRecieved);
printer.flush();
System.out.print(printer.checkError());
closeStreams();
}
private void openStreams() throws IOException{
writer = new FileWriter(file,true);
buffer = new BufferedWriter(writer);
printer = new PrintWriter(buffer);
}
private void closeStreams() throws IOException{
printer.flush();
printer.close();
buffer.close();
writer.close();
}
public void writeToFile(Purchase purchase,String dir) throws Exception{
file = new File(dir);
if(!file.exists()){
file.createNewFile();
}
openStreams();
printer.println(purchase.getName() + " По цене: " + purchase.getPrice() + "руб");
closeStreams();
}
The for loops work, but the lines. It really confuses me!
I have tried checkError(
) and I get true
, but that still doesn't help.
Can someone please explain what am I doing wrong?
回答1:
Why are you opening and closing stream in your writeToFile call ? Shouldn't you open the streams in writeFooter() before the for loop, put a try block around the writing code, and close them in a finally section .
The way I see it, You've openedstream first in the writeFooter, the you write printer.println("Проданные товары: ");, and then your for loop's first iteration calls writeToFile, will again open the non-closed stream, that will surely overwrite the first printed line.
Opening and closing File for writing one line is way too inefficient.
You need something like
writeFooter(...) {
try {
openStreams();
writeToFile();
} finally {
closeStream();
}
}
Where writeToFile simply writes , doesn't open or close stream, and closeStream safely closes the streams, i.e. check for null etc.
回答2:
public static void studentAdd() throws IOException ,ClassNotFoundException{
DataOutputStream output = new DataOutputStream(new FileOutputStream("Student.txt"));
PrintWriter pr = new PrintWriter("Student.txt");
Student7 student[] = new Student7[total];
int STOP = 999;
int stdID;
int age;
String address;
String gender;
String name;
Scanner input = new Scanner(System.in);
System.out.println("Please type student ID or 999 to quit");
stdID = input.nextInt();
try {
while(stdID != STOP) {
input.nextLine();
output.writeInt(stdID);
pr.print(stdID + "#");
System.out.println("Please type student name");
name = input.nextLine();
output.writeUTF(name);
pr.print(name + "#");
System.out.println("Please type student age");
age = input.nextInt();
output.writeInt(age);
input.nextLine();
pr.print(age + "#");
System.out.println("Please type student gender");
gender = input.nextLine();
output.writeUTF(gender);
pr.print(gender + "#");
System.out.println("Please type student address");
address = input.nextLine();
output.writeUTF(address);
pr.print(address + "#");
pr.println();
System.out.println("Please type student ID or 999 to quit");
stdID = input.nextInt();
}
; pr.close();
output.close();
} catch (IOException e) {
System.err.println("Error is" + e.getMessage());
} catch(InputMismatchException e) {
System.err.println("Invalid Data Entry");
}finally {
studentMenu();
}
} //end of stuadd
来源:https://stackoverflow.com/questions/13745260/printwriter-not-writing-to-file-java