How to have the java applet run a different calculation depending on which JTextfields are filled?

Question

I am fairly new to java (and stack overflow) so please bear with me. I am trying to create a physics projectile motion calculator which also outputs a graph of the motion. I want to have JTextfields in which the user can enter some or all of the following conditions: initial angle, initial speed, mass, range, maximum height. If the user does not enter all of the values, I want the program to fill in the remaining fields. So for example, if the user enters initial angle, initial speed and mass then I want it to calculate the range and max height. I know how to do everything described except one thing: I don't know how to have the program confirm which fields are filled and then, based on that, run the necessary calculation/method to find the missing values . I know how to use .trim().isEmpty() and I thought maybe I could use that along with some kind of boolean array or something? I searched around and couldn't find any answers. Anybody have any ideas?

Any help appreciated! Let me know if I need to provide a SSCCE (I didn't think it would be especially helpful for this question)

Edit: It seems my wording was unclear, I apologize for that. I know how to determine if a field is empty, what I need to know is how to have the program decide what calculation method to run depending on the combination of filled/unfilled fields. This is because the equations are such that I need at least 3 out of the 5 variables to calculate the others.

So for example, if the user enters the mass, angle and range then I need to call a specific method to calculate the height and initial speed. However if the user enters mass, angle and speed then I need to call a different method to calculate the height and range. Note that although height is missing in both of the above cases, I need to call different methods in each case because the combination of filled/unfilled fields is different.

JTextfield inputMass, inputAngle, inputSpeed, inputRange, inputHeight:

JButton goButton;

public void init(){
      //setup GUI
      goButton.addActionListener(this);
}

public void actionPerformed(ActionEvent click){
        Object src = click.getSource();
        if(src == goButton){
        boolean isMass = inputMass.trim().isEmpty;
//repeat for all fields
//some code to call a certain method based on which fields are filled
  }
}

I am thinking about making a boolean array and calling a method if the array matches so and so (note that there are ten possible combinations of three filled fields).

Answer 1

Using .trim().isEmpty() would work. Try implementing something as follows:

if (massTextField.getText().trim().isEmpty()) {
    //Call method to determine mass.
}
else if (rangeTextField.getText().trim().isEmpty()) {
    //Call method to determine range.
}

...and so on, for each TextField you want to test.

Hope this helps.

EDIT:

The boolean array idea would work. I cannot think of a very nice, flexible way to implement this solution, as it requires that you know exactly which variables are missing, and must calculate the answer differently depending on that case.