编辑文字未返回负值

Question

I'm calling this method in my android app:

public void Subtraction() {
    text.setText("");
    long total = num1 - num2;
    text.setText(Long.toString(total));
}

Now, when I calculate say 15-20, i don't get -5, but rather I get 0.

num1 and num2 are declared as longs.

Does anyone know why?

Thanks for your time!

EDIT: I'm getting num1 and num2 from user input in the text field :

// Subtraction case
        case R.id.buttonsubtract:
            division = false;
            addition = false;
            multiply = false;

            num1 = Long.parseLong(text.getText().toString());
            num2 = Long.parseLong(text.getText().toString());
            text.setText(text.getText() + "-");
            subtraction = true;
            break;

Answer 1

The reason your value is 0 is because both num1 & num2 are being fetched from the same text field ' text ' Hence they have the same value.

So say if user entered a value 4 in EditText field text then num1 & num2 will have the same value.

If you have separate text fields for user to enter num1 & num2 , then you should read values from those separate EditText fields.

If you want to use only one text field, there are multiple ways to handle it, one simple way is as follows (I am assuming you are working on long values only) :

1) Initialize a class variable long leftOperand = 0; 2) When user click on + , _ , * , / then put the value of the variable in text field in the variable leftOperand .

 leftOperand  = Long.parseLong(text.getText().toString());

Also store the operation that user wants to perform (say in the form of an enum).

3) Now when user presses '=' then just compute the value long newValue = Long.parseLong(text.getText().toString());

long output = leftOperand   (operation) newValue ;