Collections doubt(Niko's blog)

[Eric Nadar]

Hello
The following code gives the output 1 on compilation.

public static void main(String[] args) {
    SortedMap<String, Integer> map = new TreeMap<String, Integer>();
    map.put("B", 1);
    System.out.print(map.put("B", 2));
}

Why is the output 1?
Also when i tweaked the code a bit,

 SortedMap<String, Integer> map = new TreeMap<String, Integer>();
    System.out.print(map.put("B", 1));
    System.out.print(map.put("B", 2));

I got null 1 as output.I'am not able to understand what's happening!

[Seetharaman Venkatasamy]

from JavaDoc of java.util.Map#put

Returns:
the previous value associated with key, or null if there was no mapping for key.
(A null return can also indicate that the map previously associated null with key, if the implementation supports null values.)

[Sumit Patil]

From Javadocs, the put method returns

the previous value associated with key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with key.)

Source

Seetharaman bet me by few seconds.

[Matthew Brown]

Have you checked the documentation for TreeMap.put? See java.util.TreeMap#put(K, V). I think that explains it fairly well:

Returns:
the previous value associated with key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with key.)

Edit: too slow - sorry for the repetition!

[Seetharaman Venkatasamy]

wow...hat-trick replies...

[Eric Nadar]

Wow! Thanks.You guys are great! Perfectly understood

[Matthew Brown]

As a general rule, if you don't understand the behaviour of a class or method in the core libraries, the first port of call should be the Javadocs. If they don't explain it, or if you don't understand them, then that's the time to ask on a forum. Otherwise you risk being told to RTFM .

[Eric Nadar]

Oh! Sorry!! Will read the Java docs first next time. Thanks!!