标准输入 - java中Scanner的hasNext()的疑问

Answer 1

第一個問題，兩段程式碼的差別在於阻塞的位置不同，加上一行輸出程式碼就可以很明顯地看到差異。

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());
        }
    }
}

另，hasNext()方法會阻塞，不代表next()方法就不會阻塞。

/**
 * 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();
    }
}

第二個問題，想要結束循環，在Windows環境下，需要輸入Ctrl+Z；而在Unix環境下，需要輸入Ctrl+D。請注意，這是輸入，而不是對控制台進行操作。這相當於向控制台輸入一個字符，這個字符代表EOF，此時hasNext()方法返回false，循環結束。

Answer 2

阻塞位置不一樣