如何在Java中使整数值自动递增？

Question

I have a text file which has records like this:

1 Hamada PEPSI
2 Johny PEPSI

the format of these records is like this:

int id, String name, String drink

I wrote a small method to add records to this text file but id must be unique for every record

for example: these records are not acceptable:

1 Hamada PEPSI
2 Johny PEPSI
1 Terry Milk

here is my code:

public void addProduct(int id, String name, String drink)
{
Formatter x = null;
try{
FileWriter f = new FileWriter("C:\\Users\\فاطمة\\Downloads\\products.txt", true);
x = new Formatter(f);
x.format("%d %s %s %s%n",id,name,drink);
x.close();
}
catch(Exception e)
{
System.out.println("NO Database");
}
}

How to make id be auto-increment when entering new record?

for example:

1 Ahmed PEPSI
2 Hamada PEPSI
3 Johny Milk
4 Terry Milk
5 Jack Miranda
6 Sarah Juice

Answer 1

Ugly code. You're a beginner, so you need to know that readability matters. Pay attention to format.

Don't print message to System.out. Always print a stack trace at minimum in a catch block.

private static int AUTO_INCREMENT_ID = 1;

public void addProduct(String name, String drink) {
    Formatter x = null;
    try {
        FileWriter f = new FileWriter("C:\\Users\\فاطمة\\Downloads\\products.txt", true);
        x = new Formatter(f);
        x.format("%d %s %s %s%n",AUTO_INCREMENT_ID++,name,drink);
        x.close();
    } catch(Exception e) {
        e.printStackTrace();
    }
}

More bad code: Can't change file; don't close resources.

Answer 2

Finally i found an answer for my question, hope this be useful for other programmers.

this is the code:

public void addProduct(String name, String drink)
{ 
int max = 0;
Scanner y = null;
try{
y = new Scanner(new File("C:\\Users\\فاطمة\\Downloads\\products.txt"));
while(y.hasNext())
{
int a = y.nextInt(); // id
String b = y.next(); // name
String c = y.next(); // drink
max = a;
}
y.close();
}
catch(Exception e)
{
e.printStackTrace();
}
Formatter x = null;
try{
FileWriter f = new FileWriter("C:\\Users\\فاطمة\\Downloads\\products.txt", true);
x = new Formatter(f);
x.format("%d %s %s%n",++max,name,drink);
x.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}

Explanation: we create a variable called max and initialize it to zero .. well ... now if it was the first time to create file and adding records to it, first id will be 1 for the first record...

if text file is already exists... then the program will search for max id and increment it .... for example:

  1 Hamada PEPSI
  2 Johny MILK

then when adding new record it will have the id = 3

if there is any errors, please tell me guys :)

thanks to all of you :)