import java.util.scanner,从方法内部使用java.util.Scanner会导致运行时错误

Why would the following code give me a runtime error? It gives me a NoSuchElementException when the method is called the second time. It works fine if I delete the call to stdin.close(), but then Eclipse gives a warning that the resource is not closed.

Code:

import java.util.Scanner;

public class st {

public static void main(String[] args) {

System.out.println("First call");

getInt("Enter first int (1-10): ");

System.out.println("Second call");

getInt("Enter second int (1-10): ");

}

/**

* Reads an integer number from the keyboard.

*

* @param prompt the string to display as a prompt.

* @return the integer number entered at the keyboard.

*/

public static int getInt(String prompt) {

Scanner stdin = new Scanner(System.in);

System.out.print(prompt);

int val = stdin.nextInt();

stdin.close();

return(val);

}

}

// END

Output:

>java st

First call

Enter first int (1-10): 5

Second call

Enter second int (1-10): Exception in thread "main" java.util.NoSuchElementException

at java.util.Scanner.throwFor(Unknown Source)

at java.util.Scanner.next(Unknown Source)

at java.util.Scanner.nextInt(Unknown Source)

at java.util.Scanner.nextInt(Unknown Source)

at st.getInt(st.java:24)

at st.main(st.java:9)

>

Version:

>java -version

java version "1.7.0_21"

Java(TM) SE Runtime Environment (build 1.7.0_21-b11)

Java HotSpot(TM) 64-Bit Server VM (build 23.21-b01, mixed mode)

>

Thanks

Brian

解决方案

AS @MikePrecup says, when you close the first Scanner (stdin), you are also closing System.in, therefore the second Scanner can no longer read from it and a NoSuchElementException is thrown.

However, I would suggest another option: use a single scanner declaring it as a class variable.

public class st {

private static Scanner stdin = new Scanner(System.in);

public static void main(String[] args) {

System.out.println("First call");

getInt("Enter first int (1-10): ");

System.out.println("Second call");

getInt("Enter second int (1-10): ");

}

/**

* Reads an integer number from the keyboard.

*

* @param prompt the string to display as a prompt.

* @return the integer number entered at the keyboard.

*/

public static int getInt(String prompt) {

System.out.print(prompt);

int val = stdin.nextInt();

stdin.close();

return(val);

}

}

// END