PrintWriter的print和write方法
? public void print(String s) {
if (s == null) {
s = "null";
}
write(s);
? }
? print只是先对s==null转换为"null"
? public void println(String x) {
synchronized (lock) {
print(x);
println();
}
? }
?public void print(Object obj) { write(String.valueOf(obj));}