System clear Property doesn't work. How can it be?

Question

I really don't understand!

I run unit tests which contains cod:

  String progDir = "prog.dir";
  System.clearProperty(progDir);
  System.out.println(System.getProperty(progDir));

And on console I see prog dir path. Although there must be null.

I setting this variable in setUp block. This is junit test. This variable need for all other test but not for that, so I tried to clean it in the start of this test method. If I remove setting of this var from setUp block this test will pass.

System.setProperty work fine.

How can it be? Thanx

Answer 1

If a property is not defined in a Properties object, then getProperty will look up in the parent Properties object

Properties javadoc says:

public String getProperty(String key)

Searches for the property with the specified key in this property list. If the key is not found in this property list, the default property list, and its defaults, recursively, are then checked. The method returns null if the property is not found.

clearProperty calls Hashtable.remove since remove is not overridden in Properties so does not affect the default property list.

So it is quite possible for a cleared property to still be visible via getProperty since the System javadoc does not specify whether system Properties are layered or flat.