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W1ll
Asked: 2020-04-16 09:53:39 +0800 CST 2020-04-16 09:53:39 +0800 CST

Doubt with code evaluation in Android

  • 772

I have this code in my app, but I don't understand how it is evaluated: return chatBubble.myMessage() ? 1 : 0;,

Could someone tell me how is this?

    public int getItemViewType(int position) {
    ChatBubble chatBubble = messages.get(position);
    return chatBubble.myMessage() ? 1 : 0;
}
android

1 Answers

  1. Best Answer

    This is called in Java ternary operator , represented by the symbol ?.

    According to the Java documentation :

    It can be thought of as a shorthand for a statement if-then-else. This operator is also known as the ternary operator because it uses three operands.

    It works like this in this case:

    • If the result of chatBubble.myMessage()is true, it returns1
    • If the result of chatBubble.myMessage()is false, return0

    The ternary operator then has three parts:

    chatBubble.myMessage()      ?             1           :           0;
        ^                   ^             ^                       ^
   Operando 1                         Operando 2              Operando 3
Expresión a evaluar      Operador    Si Expr es TRUE        Si Expr es FALSE

    Expressions for this operator are written like this:

    To the left of ?is the expression or value to be evaluated ( Expr ), to the left of :is the resulting value if the evaluation of Expr is true, to the right of :is the resulting value if the evaluation of Expr to be false.

    And since you use it with return, it will return the result 1or 0that it has exited the evaluation.

    NOTE:

    This is the simplest form of ternary operator. There are more complex evaluations, nested operators etc. The truth is that they greatly simplify the code.

    On that one line, you evaluate something that would otherwise have to be written like this:

    if ( chatBubble.myMessage() ) {
    return 1;
} else { 
    return 0;
}

    We are talking about changing 5 lines of code for a single one, thanks to the ternary operator.

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