问几个java问题What will be the output on compiling/running the following code?

public class MyThread implements Runnable
{
String myString = "Yes ";

public void run()
{
this.myString = "No ";
}

public static void main(String[] args)
{
MyThread t = new MyThread();
new Thread(t).start();

for (int i=0; i < 10; i++)
System.out.print(t.myString);
}
}

问题是，myString 不是public的，为什么main()最后一行不会报错呢？ 我把main()移到另一个class中，也能run，都有点学糊涂了我 :P


第二个问题

public class Static
{
static
{
int x = 5;
}

static int x,y;
public static void main(String args[])
{
x--;
myMethod();
System.out.println(x + y + ++x);
}

public static void myMethod()
{
y = x++ + ++x;
}
}

这里有两个static, 一个是static{ int x = 5;} 另一个是static int x;
如何拿到在那个static{}中的x？ 还想知道前者有什么用吗？


多谢!![bigfox (6-29 17:04, Long long ago)] [ 传统版 | sForum ][登录后回复]1楼

Answers:1) Of course no error, since you are accessing t.myString inside t itself! Note that your main method is part of the MyThread class. Furthermore, Java's default access specification for member variables and methods is NOT private! The default specification allows access from any class in the same package. As your MyThread class is not in any package (effectively in the so-called "global" package), and I suppose so is your other test classes, myString is accessible.

2) The x in the first static scope cannot be accessed, because it is destroyed straightaway after it is declared! Note that static {...} structure is usually useful only in the global scope, i.e., outside any class. Basically, it provides static initialization routines to be executed before everything else (of course, there are still necessary initializations like class loading before this). Don't confuse the static code fragment with static member variable of a class.[Flying (6-29 18:03, Long long ago)] [ 传统版 | sForum ][登录后回复]2楼

java tutorial from Sun is always a good resource to consultFirst q: t is an local variable, t.MyString is accessing a member variable of t via t. Thus it is nothing related to public/protected/private limitation.


Second q: static initialization blocks are used for initilize a class member.

Note declaration also do the initialization for class member/instance member:
byte,short,int,long -> 0
float, double, -> 0.0
bool -> false
char -> empty character
object -> null


If you really want to access the thing in static{}, put static statements before define class member.

Seems you are doing SCJP, if yest, better read Java tutorial carefully. [香陵居士 (6-29 21:46, Long long ago)] [ 传统版 | sForum ][登录后回复]3楼

(引用 香陵居士:java tutorial from Sun is always a good resource to consultFirst q: t is an local variable, t.MyString is accessing a member var...)What's SCJP?Sun Certified Java Programmer?

Is it an interesting cert?[Flying (6-30 11:30, Long long ago)] [ 传统版 | sForum ][登录后回复]4楼

ur mails...got a lot...how?[小蹦 (6-30 13:00, Long long ago)] [ 传统版 | sForum ][登录后回复]5楼

(引用 小蹦:ur mails...got a lot...how?)really? help me pass them to 阿修罗 bah 3x 3x[bigfox (6-30 15:36, Long long ago)] [ 传统版 | sForum ][登录后回复]6楼

(引用 Flying:Answers:1) Of course no error, since you are accessing t.myString inside t itself! Note that your main method is part of the MyT...)are u saying thatany var(s) declared within static{} will not be reachable any more after the control flow gets out of that block?

pls correct me if i am wrong. 3x :D[bigfox (6-30 16:01, Long long ago)] [ 传统版 | sForum ][登录后回复]7楼

(引用 Flying:What's SCJP?Sun Certified Java Programmer? Is it an interesting cert?)not suit for u at all.it is only for junior programmers, but it is the prerequisite cert for SCJD SCBCD etc.[bigfox (6-30 16:01, Long long ago)] [ 传统版 | sForum ][登录后回复]8楼

(引用 bigfox:really? help me pass them to 阿修罗 bah 3x 3x)只要不是来自PR/UOB, 就不是很急.如果他没空，那我就找个时间过去一趟 huhu :)

你加我msn吧, smallfox33@ [bigfox (6-30 16:56, Long long ago)] [ 传统版 | sForum ][登录后回复]9楼

(引用 bigfox:not suit for u at all.it is only for junior programmers, but it is the prerequisite cert for SCJD SCBCD etc.)That's it lo... there are always long staircases to climb...[Flying (6-30 22:10, Long long ago)] [ 传统版 | sForum ][登录后回复]10楼

(引用 Flying:That's it lo... there are always long staircases to climb...)Hoho, if you are good enough to get SCEA, can got for it directly. ;)[香陵居士 (7-1 0:39, Long long ago)] [ 传统版 | sForum ][登录后回复]11楼

(引用 bigfox:are u saying thatany var(s) declared within static{} will not be reachable any more after the control flow gets out of that bloc...)Yes.Static initializer blocks behave like static methods in the class, with all method names, argument lists, and return types stripped.

All static initializers declared in a class are executed exactly once, in the order of their declarations, when the class is first loaded. Therefore, static initializer are popular when you need to initialize static class member variables with logic that exceeds what a single-line expression initializer can do.

Therefore, with the basic scoping rule, I suppose local variables should not be accessible from outside of a static initializer block.[Flying (7-1 8:22, Long long ago)] [ 传统版 | sForum ][登录后回复]12楼