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Thread: Operate on list`s objects

  1. #1
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    Question Operate on list`s objects

    Dear Friends...Hello..!
    Look at this example..:

    PHP Code:
    import java.util.ArrayList;
    ArrayList<Object> list = new ArrayList<Object>();
    list.
    add(10);    // boxing converts to instance of Integer
    list.add("Bisons");
    list.
    add(2.3);    // boxing converts to instance of Double

    for (Object o : list)
      
    System.out.println(o); 
    We just can print a list?
    I mean can`t operate on each object(depends on their types)?


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    Default Re: Operate on list`s objects

    What is the problem you're having? I've put this into a class and it compiles and prints ok.

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    Default Re: Operate on list`s objects

    Quote Originally Posted by samfin View Post
    What is the problem you're having? I've put this into a class and it compiles and prints ok.
    yeah ..there`s no problem for printing..but..for example imagin that list[i] is belong to class Class1
    PHP Code:
    class Class1 {
    private 
    int a;

    can I use list[i].a ?
    or just can print list[i] ...?

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    Default Re: Operate on list`s objects

    I'm not following you, can you post some code with the lists, variables whatever, that shows what you're asking please

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    Default Re: Operate on list`s objects

    Quote Originally Posted by samfin View Post
    I'm not following you, can you post some code with the lists, variables whatever, that shows what you're asking please
    It`s just an example..I mean what can i do with list`s objects except printing..!?

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    Default Re: Operate on list`s objects

    The short answer is don't mix object types in a list like that. You can only store objects of different class types if you store them as an Object, which means you can only retrieve them as an Object, so you're very limited as to what you can do with them.

    It is possible to use the Reflection API to discover the real type of the object you want to use, then cast it to that type to use it. I strongly advise against this, it should be the last resort when there is no alternative.

    There are far better alternatives, but it depends on exactly what you're trying to achieve. The ideal situation is to store a class type that has the methods that you want to use. This is usually done by defining an interface with the methods you want and having various classes implement the methods in their own way. Then the list can be specified to store the interface type and all classes that implement the interface can be used with it.

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