weired thing with string function on my edittext

I have a complicated equation, and there is several edit texts that you can enter your numbers in it , and the final result depends on which text will be filled with numbers so the texts may be filled partially or fully, assume that

text1=height,

text2=weight,

text3=width..

if i enter numbers on only width and height, the app will go with area equation

if i enter numbers on only height and weight , the app will go with size equation ... etc

so how to make like (if) condition, that make the app see if specific texts only filled go with specific equation and without crushed because no numbers with the other texts ??!!!? like if:

height:" 10"

weight: "5"

width: " "

//don't go with area equation // go with size eqation

<<<>>>>> i think about using something like this if(width!= '' or height!= ''){//do nothing} but how to make "or" on android ?!