javac数据流分析的奇怪的假阳性 [英] Weird false-positive of javac data flow analysis

问题描述

我有以下形式的代码：

  class Test {
 private final A t; 
 
 public Test（）{
 
 for（...：...）{
 final A u = null; 
} 
 
 t = new A（）; 
} 
 
私人类A {} 
} 
  

编译器说：

 变量t可能已分配
   
 
 
 
 
 
 
 
 
将循环内容更改为 A u = null  
 
 
删除循环（但保留 final A u = null; ）
 
 
经典计数循环
 
 
 
 
 
这是怎么回事？
 
 
 
 注意：我无法得到最小的例子，导致错误，所以有可能是环境（约1400 loc）有问题。我不能看到什么可以打扰 t 的初始化，虽然，因为 t 写到其他地方。 p> 
 
 
有趣的事实：IntelliJ IDEA说如果我删除它，变量'u'可以有'final'修饰符...。
 
 
 
我使用javac 1.6.0_26。
 
 
 
 更新：最小：
  import java.util.List; 
 
 class A {
 private final boolean a; 
 
 public A（）{
 for（final Object o：new Object [] {}）{
 final Object sh = null; 
} 
 
 a = true; 
} 
 
 class B {
 private final Object b1; 
 private final Object b2; 
 
 B（）{
 b1 = null; 
 b2 = null; 
} 
} 
} 
  
 c $ c> javac 1.6.0_26 但编译在 javac 1.7.0_02 。 
 
 
 
请注意，你可以做任何
 
 
 
 
 
删除任何一个成员 
 
删除中的 （） 
 
 
用替换循环，例如  for（int i = 0; i <100; i ++）{...}  
 
 
 
 $ b b 
它会编译。
解决方案
由于问题在Java 7中已修复， Java 6编译器。
 
I have code of the following form:
class Test {
  private final A t;

  public Test() {

    for ( ... : ... ) {
      final A u = null;
    }

    t = new A();
  }

  private class A {}
}
Compiler says:
variable t might already have been assigned
Interestingly, if I perform any of the following changes to the loop it works out! 


Change the loop's content to A u = null
Remove the loop (but keep final A u = null;)
Replace the foreach-style loop with a classic counting loop


What is going on here?

Note: I could not get the minimal example to cause the error so there is probably something wrong with the "environment" (about 1400 loc). I can not see what could disturb the initialisation of t, though, as t is written to nowhere else.

Fun fact: IntelliJ IDEA says "Variable 'u' can have 'final' modifier..." if I remove it.

I use javac 1.6.0_26.

Update: There you go, this example so so minimal:
import java.util.List;

class A {
  private final boolean a;

  public A() {
    for ( final Object o : new Object[] {} ) {
      final Object sh = null;
    }

    a = true;
  }

  class B {
    private final Object b1;
    private final Object b2;

    B() {
      b1 = null;
      b2 = null;
    }
  }
}
Fails to compile on javac 1.6.0_26 but compiles on javac 1.7.0_02. So I guess I hit some wicked corner case of ... something?

Note that you can do any of


Remove any one member
Remove final inside the loop in A()
Replace the loop with a normal for loop, e.g. for ( int i=0; i<100; i++ ) { ... }


and it will compile.
解决方案
As the problem is fixed in Java 7, it is probably a bug in the Java 6 compiler.

                        
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