为什么以下代码会给我一个运行时错误?第二次调用该方法时,它给了我一个NoSuchElementException
。如果删除对stdin.close()
的调用,效果很好,但是Eclipse发出警告,指出资源未关闭。
码:
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
输出:
>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)
>
版:
>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)
>
谢谢
布赖恩
最佳答案
就像@MikePrecup所说的那样,当您关闭第一个扫描仪(stdin
)时,您也正在关闭System.in
,因此第二个扫描仪无法再读取它,并且会抛出NoSuchElementException
。
但是,我建议另一个选择:使用单个扫描程序将其声明为类变量。
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