伊谢尔伦2017-04-17 14:48:30
The first question is that the difference between the two pieces of code lies in the different blocking positions. You can clearly see the difference by adding a line of output code.
Test.java
import java.util.Scanner;
public class Test {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
while(s.hasNext())
{
System.out.print("You inputted: ");
System.out.println(s.next());
}
}
}In addition, the hasNext() method will block, but it does not mean that the next() method will not block.
/**
* Returns true if this scanner has another token in its input.
* This method may block while waiting for input to scan.
* The scanner does not advance past any input.
*
* @return true if and only if this scanner has another token
* @throws IllegalStateException if this scanner is closed
* @see java.util.Iterator
*/
public boolean hasNext() {
ensureOpen();
saveState();
while (!sourceClosed) {
if (hasTokenInBuffer())
return revertState(true);
readInput();
}
boolean result = hasTokenInBuffer();
return revertState(result);
}/**
* Finds and returns the next complete token from this scanner.
* A complete token is preceded and followed by input that matches
* the delimiter pattern. This method may block while waiting for input
* to scan, even if a previous invocation of {@link #hasNext} returned
* <code>true</code>.
*
* @return the next token
* @throws NoSuchElementException if no more tokens are available
* @throws IllegalStateException if this scanner is closed
* @see java.util.Iterator
*/
public String next() {
ensureOpen();
clearCache
while (true) {
String token = getCompleteTokenInBuffer(null);
if (token != null) {
matchValid = true;
skipped = false;
return token;
}
if (needInput)
readInput();
else
throwFor();
}
}Second question, if you want to end the loop, you need to enter Ctrl+Z in the Windows environment; and in the Unix environment, you need to enter Ctrl+D. Note that this is input, not manipulation of the console. This is equivalent to entering a character into the console, which represents EOF. At this time, the hasNext() method returns false and the loop ends.
