Github user jacek-lewandowski commented on the pull request:
https://github.com/apache/spark/pull/4220#issuecomment-72272628
Look at this simple example:
```scala
val parent = new Properties()
parent.setProperty("test1", "A")
val child = new Properties(parent)
child.put("test2", "B")
val copy = new Properties()
copy.putAll(child)
child.getProperty("test1")
child.getProperty("test2")
copy.getProperty("test1")
copy.getProperty("test2")
```
which will result in:
```
scala> res3: String = A
scala> res4: String = B
scala> res5: String = null
scala> res6: String = B
```
In other words: `new Properties(oldProperties)` initialises a new
properties by setting oldProperties as a parent (defaults). On the other hand
`new Properties().putAll(oldProperties)` copies only those properties which
were explicitly set and cuts the whole hierarchy with defaults. Only cloning
gives you the same object.
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