在JShell上执行时，同一语句的不同行为

问题描述

我正在研究一个将两个类的引用相互存储的问题

I was working on a problem to store reference of two classes within each other

例如:

class A {
B b;
A(B b){
this.b = b;}
}

class B {
A a;
B(A a){
this.a = a;}
}

public static void main(String...s){
A a = new A(new B(null));
a.b.a = a;
}

现在，如果我使用下面的语句，而不是上面的初始化:

Now if instead of above initialisation, if I use below statement:

A a = new A(new B(a));

我遇到了一个很明显的错误:

I got below error which is quite obvious:

Main.java:19: error: variable a might not have been initialised
        A a = new A(new B(a));

但是如果我在JShell上尝试同样的方法，它就可以正常工作(只是要确保variable a从未被初始化，所以我在执行该语句之前先检查了variable a，该语句确认它没有被初始化:

But if I try the same on JShell, it works just fine (Just to be extra sure that variable a has never been initialized, I checked for variable a just before executing the statement which confirms that it was not initialized before:

可能是我在这里遗漏了一些东西，但是请问有人可以帮助我了解为什么在JAVA中执行同一条语句会有两种不同的行为.

May be I am missing something here, but can some one please help me to understand why there are two different behaviours of the same statement being executed in JAVA.

了解此问题的一种简单方法是，在Jshell中允许使用以下语句，但在常规程序中不允许:

A simple way to understand this problem is that below statement is allowed in Jshell but not in normal program:

var somevar = somevar;

推荐答案

尽管我完全同意@Andreas的回答，这是JShell当前正在使用的初始化方式所期望的，但我与@Dawood的观点相同. JShell应该尽可能接近普通编译器，否则有时可能会不确定，因此使用起来不安全.

Though I totally agree with @Andreas answer above that this is expected with the way initialisation is currently working in JShell, I also have the same view as @Dawood that JShell should work to normal compiler as close as possible, otherwise it can sometime be uncertain and hence unsafe to use.

对于这种特殊情况，我向Oracle提出了一个问题，现在它已被接受为正式bug.您可以在此处跟踪有关此错误的更多信息:

For this particular scenario, I raised an issue with Oracle and it has now been accepted as an official bug. You can track more about this bug here:

https://bugs.java.com/bugdatabase/view_bug .do?bug_id = JDK-8200567

希望此问题将在即将发布的JShell版本中很快得到解决.

Hope that this will be resolved soon in the upcoming releases of JShell.

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