IntelliJ IDEA: Boolean method XX is always inverted

try to return false if bluetoothAdapter is null otherwise return the output of isEnabled()

public static boolean isBlueToothEnabled(){
    final BluetoothAdapter bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
    if(bluetoothAdapter == null){
        return false;
    }
    return bluetoothAdapter.isEnabled();
}

Read more:

In Clean Code, Robert Martin writes, “Negatives are just a bit harder to understand than positives. So, when possible, conditionals should be expressed as positives.” (Martin, [G29]). IntelliJ IDEA has three inspections to help you stay positive.

https://blog.jetbrains.com/idea/2014/09/the-inspection-connection-issue-2/ (Entry #4 Avoiding negative Conditionals)

https://www.jetbrains.com/help/idea/2016.1/invert-boolean.html

Summary: Method always called like !method(). It's more efficient to have less number of computation. Refactor the method and return oppositely and call the method without (!)

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Why it happens

If we have a method foo()

    boolean foo()
    {
        if(condition == true)
            return true;
        else
            return false;
    }

And is only called like !foo(),

    class A
    {
        if(!foo())
            do something;
        ...
        if(!foo())
            do something else;
    }

Because we only call !foo() and did not call foo().

The warning asks us to use foo() in a positive way.

Remove the warning

By inverting the return value of the method foo(),

    boolean foo()
    {
        if(condition == true)
            return **false**;
        else
            return **true**;
    }

Now call the method

    class A
    {
        if(foo())
            do the same thing;
    }