我看了jdk6中System.java的源码，这么定义我们经常用的out:
public final static PrintStream out = nullPrintStream();
然后nullPrintStream()方法如下
private static PrintStream nullPrintStream() throws NullPointerException {
if (currentTimeMillis() > 0) {
return null;
}
throw new NullPointerException();
}
整个方法跑完不是回复null就是抛Exception，那我们平时还怎么用的System.out.println(..)之类的方法？
------解决方案--------------------
不要100％相信你看到的
------解决方案--------------------
其实是一样的。。。你不要相信。
------解决方案--------------------
看源码总得先看注释吧，你有没有看注释？
/**
* The following two methods exist because in, out, and err must be
* initialized to null. The compiler, however, cannot be permitted to
* inline access to them, since they are later set to more sensible values
* by initializeSystemClass().
*/