问题描述
如果我关闭一个扫描仪对象并制作一个新的对象,然后尝试读取更多输入,我将得到NoSuchElementException
异常.
If I close one scanner object and make a new one and try to read some more input, I'm getting the NoSuchElementException
exception.
我的代码工作正常,但是如果我不关闭扫描仪,它会警告我.但是,如果我关闭它以消除警告,我也会关闭System.in
...如何避免这种情况?
My code works fine but it gives me a warning if I don't close the scanner. However, if I close it to get rid of the warning, I also close System.in
... How do I avoid this?
还有,不关闭扫描仪会有什么后果吗?
Also, are there any consequences of not closing the scanner?
这是我的代码:
这是NameAddressExists()方法:
This is the NameAddressExists() method:
public void NameAddressExists() {
System.out.println("Enter name");
Scanner sc = new Scanner(System.in);
String n = sc.next();
System.out.println("Enter address");
String a = sc.next();
int flag = 0;
for(int i = 0; i < count; i++) {
if(array[i].name .equals(n) && array[i].address .equals(a)) {
System.out.println("True");
flag = 1;
}
}
if(flag != 1) {
new Agency(n, a);
}
sc.close();
}
这是PanNumberExists()方法:
This is the PanNumberExists() method:
public boolean PanNumberExists() {
Scanner s = new Scanner(System.in);
String n = "";
System.out.println("Enter the 5 digits");
try {
n = s.nextLine();
}catch(Exception e) {
System.out.println(e);
}finally {
s.close();
}
if(n .equals(this.PAN.subSequence(4,9))) {
return true;
}
else {
return false;
}
}
这些方法是从以下main()方法调用的:
These methods are called from the following main() method:
public static void main(String args[]) {
Agency obj1 = new Agency("XYZ", "ABCD");
Agency obj2 = new Agency("XYZ", "ABCDEFG", "+91083226852521", "ab 1234567", "abcd12345ab");
// Agency obj3 = new Agency("XYZ", "TSRK", "36", "ab 1234567", "abcd12345ab");
obj1.NameAddressExists();
System.out.println(obj2.PanNumberExists());
}
如您所见,我首先调用NameAddressExists()方法,在其中打开,使用和关闭名为'sc'的Scanner
.这可以正常工作,并给我正确的输出.接下来,我调用PanNumberExists()方法,在其中打开另一个名为's'的Scanner
,并尝试使用它从用户那里获取一些输入.这是我收到NoSuchElementException
异常的地方.如果我在NameAddressExists()方法中将Scanner
'sc'保持打开状态,则不会收到此错误.
As you can see, I first call the NameAddressExists() method, in which I open, use and close a Scanner
named 'sc'. This works fine and gives me the correct output. Next, I call the PanNumberExists() method, in which I open another Scanner
named 's' and try to use it to get some input from the user. This is where I receive the NoSuchElementException
exception. If I leave the Scanner
'sc' open in my NameAddressExists() method, then I don't get this error.
推荐答案
Scanner scan = new Scanner(new FilterInputStream(System.in) {
@Override
public void close() throws IOException {
// do nothing here !
}
});
或者,通过实现自定义装饰器只需忽略close()
.
Or , Just ignore close()
by implementing custom decorator.
public class UnClosableDecorator extends InputStream {
private final InputStream inputStream;
public UnClosableDecorator(InputStream inputStream) {
this.inputStream = inputStream;
}
@Override
public int read() throws IOException {
return inputStream.read();
}
@Override
public int read(byte[] b) throws IOException {
return inputStream.read(b);
}
@Override
public int read(byte[] b, int off, int len) throws IOException {
return inputStream.read(b, off, len);
}
@Override
public long skip(long n) throws IOException {
return inputStream.skip(n);
}
@Override
public int available() throws IOException {
return inputStream.available();
}
@Override
public synchronized void mark(int readlimit) {
inputStream.mark(readlimit);
}
@Override
public synchronized void reset() throws IOException {
inputStream.reset();
}
@Override
public boolean markSupported() {
return inputStream.markSupported();
}
@Override
public void close() throws IOException {
//do nothing
}
}
在main()
中使用时,
public static void main(String[] args) throws Exception {
System.setIn(new UnClosableDecorator(System.in));
}
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