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Doubt on interface

Martin Arun Paul Perumala
Greenhorn

Joined: Dec 10, 2008
Posts: 14
The following code is simple trying to take 2 variables and adding, substracting and multiplying them using interface concept.

In the demo class I want to use "function chaining" like a1.setdata().add().sub().mul(). Is it possible? I tried to do it but I guess we have to create another class. please help me

Thank you








[edit]Add code tags. CR[/edit]
[ December 13, 2008: Message edited by: Campbell Ritchie ]
Ulf Dittmer
Marshal

Joined: Mar 22, 2005
Posts: 42031
    
  64
If you want to chain methods, then they can't be "void" - in other words, return nothing. They should return the result of the previous calculation - what in the code is stored in "z".

There's no point really in using an interface here. You could use one if all the individual operations (plus, minus, multiply, ...) each had their own class; but that would be a contrived use.
[ December 13, 2008: Message edited by: Ulf Dittmer ]

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Martin Arun Paul Perumala
Greenhorn

Joined: Dec 10, 2008
Posts: 14
so can we change the return type (void) of the methods in the interface class to something else like object type.?
Rob Spoor
Sheriff

Joined: Oct 27, 2005
Posts: 19697
    
  20

Take a look at java.lang.StringBuilder. After modifying its contents, it returns "this":

Of course you can do the same if you want to keep your contents fixed. In that case, take a look at java.math.BigInteger. A few examples:

Both can now be chained:

The first line creates one single StringBuilder object that has three strings appended to it.
The second line creates 5 BigInteger objects:
- new BigInteger("5")
- new BigInteger("6")
- the result of 5 + 6
- new BigInteger("7")
- the result of (5 + 6) * 7

In the end, "big" will contain a value of 77.


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