Description Stephan Herrmann 2011-08-11 17:03:28 EDT

Given this snippet:

Object u = new Object();
Object r = (u == null ? u : null);
System.out.println(r.toString());

the compiler reports:
----------
1. ERROR in BugXYZ.java (at line 4) 
	Object r = (u == null ? u : null);
	            ^
Null comparison always yields false: The variable u cannot be null at this location
----------
2. ERROR in BugXYZ.java (at line 5)
	System.out.println(r.toString());
	                   ^
Potential null pointer access: The variable r may be null at this location
----------

The 2nd error is misleading since there's no way how r can be non-null.

The effect is caused by incomplete analysis of the conditional expression
after finding that the condition is always false.

When constructing the same using an if statement the dead branch would
simply be skipped by null analysis. That's why the issue cannot be
reproduced using if.