Unreachable statement from the Decompiler output

Question

I decompiled an APK file, then tried to compile it and received an "Unreachable statement" compiler error, I want to know is it a obfuscator trick, or decompiler failure? How is it possible? Used dex2jar and Java Decompiler

And here is the decompiled method

public void onSensorChanged(SensorEvent paramSensorEvent) {
    float[] arrayOfFloat = paramSensorEvent.values;
    switch (paramSensorEvent.sensor.getType())
    {
    }
    do
    {
        return;
    } while (this.aDegree == arrayOfFloat[0]);
    this.aDegree = arrayOfFloat[0];
    invalidate();
}

Answer 1

It's possible because unreachable statement is a useful compile time error, not a runtime check/constraint.

The code that you decompiled might have had something like this originally:

boolean debug = true;
do {
    if(debug) {
        return;
    }
}while (this.aDegree == arrayOfFloat[0]);

The compiler is smart enough to know that debug is always true and doesn't bother with the check in the byte code (for efficiency).

Obviously my example is quite contrived, in reality it was probably more complex (although the end result is the same).