public class X implements Runnable { private int x； p

单项选择题

public class X implements Runnable {
private int x；
private int y；
public static void main（String [] args） {
X that = new X（）；
（new Thread（ that ））.start（）；
（new Thread（ that ））.start（）；
}
public void run（） {
for （；；） {
synchronized （this） {
x++；
y++；
}
System.out.println（Thread.currentThread（）.getName（） +
“x = “ + x + “， y = “ + y）；
}
}
}
What is the result？（）

A. Compilation fails.
B. The program prints pairs of values for x and y that might not always be the same on the same line （for example， “x = 2， y = 1”）.
C. The program prints pairs of values for x and y that are always the same on the same line （for example， “x = 1， y = 1”）. In addition， each value appears only once （for example， “x = 1， y = 1” followed by “x = 2， y = 2”）. The thread name at the start of the line shows that both threads are executing concurrently.
D. The program prints pairs of values for x and y that are always the same on the same line （for example， “x = 1， y = 1”）. In addition， each value appears only once （for example， “x = 1， y = 1” followed by “x = 2， y = 2”）. The thread name at the start of the line shows that only a single thread is actually executing.

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