object is not closed properly. Whats is meant by it in scanner?

Question

I used scanner for the first time. I got an error @ finish, saying that finish is not closed properly. What is meant by that. Thanks!

import java.util.Scanner;

public class inputvalue {
    public static void main(String[] args) {
        int i = 0;
        Scanner finish = new Scanner(System.in);
        int j = finish.nextInt();
        while (i < j) {
            System.out.print("hai");
            i = i + 1;
        }

    }
}

Answer 1

The compilator warns you about a potential leak of memory. You have two solutions when encountering this problem.

java-7 and latter

Use a try-with-resources block that will automatically close your stream. That'll prevent your program from having a leak in its resources.

int i = 0, j;
try(Scanner finish = new Scanner(System.in)){
    j = finish.nextInt();
}
while (i < j) {
    System.out.print("hai");
    i = i + 1;
}

---

java-6 and earlier

Use a try-finally and within the latter check if your object is null. If it's not, close it manually.

int i = 0, j;
Scanner finish = new Scanner(System.in);
try {
    j = finish.nextInt();
} finally {
    if (finish != null) {
        finish.close();
    }
}
while (i < j) {
    System.out.print("hai");
    i = i + 1;
}

Answer 2

Scanner implements Closeable interface which has a close method. All the classes implementing this interface represent that they are using resources that needs to be closed. You should therefore clsoe Scanner. One way of doing this is in the predestroy method as:

@PreDestroy
public void preDestroy {
    scanner.close();
}

The other way would be to close scanner at the end of your code as:

public static void main(String[] args) {
    int i = 0;
    Scanner finish = new Scanner(System.in);
    int j = finish.nextInt();
    finish.close();
    while (i < j) {
        System.out.print("hai");
        i = i + 1;
    }
}

Read more about Closeable here and here