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Thread: Im not sure what this is?

  1. #1
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    Default Im not sure what this is?

    Hi,

    ATM I'm just learning about making a simple window. And ive come across this:

    frame.getContentPane().add(yellowLabel, BorderLayout.CENTER);

    I understand what this code code, but I dont understand its structure, to me it looks like im calling the add() method within the getContentPane() method, is that right, can we have methods within methods?

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    Super Moderator Norm's Avatar
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    Default Re: Im not sure what this is?

    Each method in that chain of method calls starting at the left end returns an object of some type. The next method called is for that object.

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    Default Re: Im not sure what this is?

    Thank you. The getContentPane() method returns a Container object, so the add() method is for the Container object.

    Is it a general rule of Java Programming, when we have a method followed by a dot with another method, it means that the first method returns an object and the following method call is for the returned object?

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    Super Moderator Norm's Avatar
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    Default Re: Im not sure what this is?

    Sort of. It's a requirement of the compiler that all method calls be with a valid class object.
    Personally I don't care to chain a bunch of methods together like your example.

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    Default Re: Im not sure what this is?

    what other way could i do it without using a chain of methods?

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    Default Re: Im not sure what this is?

    Break it up to single statements:

    Container contr = frame.getContentPane();
    contr.add(yellowLabel, BorderLayout.CENTER);

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    Default Re: Im not sure what this is?

    Thank you.