check decimal or point Java - arrays

Question

i am working on a calculator project.
i am using a method to separate the char and numeric values.
but i am getting problem on when i have a decimal value, because result shown 0 when decimal value runs.
here is the code.
List<Double> numbers = new ArrayList<>();
List<Character> operators = new ArrayList<>();
..................
void testing() {
String userInput = "234+234+234";
/* ignore the line above its just for understanding */
/*the above works fine but if we change it to below its dont work.*/
String userInput = "234+2.3+4.2";
/* The both lines above are just for understanding actually i am getting text from edittext*/
String userInput = currentcalc.getText().toString();
for (char c : userInput.toCharArray()) {
if (!Character.isDigit(c)) {
s1 = Double.parseDouble(s2);
numbers.add(s1);
operators.add(c);
handler++;
s2 = "";
s1 = 0;
} else {
s = Character.toString(c);
s2 += s;
}
}
result();
}
result = 0.0
s and s2 are strings and s1 is double. and in my code if c is not a digit it is saving value of operator like +,- etc and else it is saving value of digits and other things. i want to know that why "." is not being save via this code and why result is showing 0.0
the result(); code is here below
void result() {
double total4 = 0;
s1 = Double.parseDouble(s2);
numbers.add(s1);
if (handler < 1) {
total4 = Double.parseDouble(currentcalc.getText().toString());
} else {
int i = 0;
for (i = 0; i < handler; i++) {
switch (operators.get(i)) {
case '/':
total3 = numbers.get(i) / numbers.get(i + 1);
total4 = total3;
numbers.remove(i + 1);
numbers.set(i, total4);
operators.remove(i);
handler--;
i--;
break;
}
}
for (i = 0; i < handler; i++) {
switch (operators.get(i)) {
case '*':
total3 = numbers.get(i) * numbers.get(i + 1);
total4 = total3;
numbers.remove(i + 1);
numbers.set(i, total4);
operators.remove(i);
handler--;
i--;
break;
}
}
for (i = 0; i < handler; i++) {
switch (operators.get(i)) {
case '+':
total3 = numbers.get(i) + numbers.get(i + 1);
total4 = total3;
numbers.remove(i + 1);
numbers.set(i, total4);
operators.remove(i);
break;
case '-':
total3 = numbers.get(i) - numbers.get(i + 1);
total4 = total3;
numbers.remove(i + 1);
numbers.set(i, total4);
operators.remove(i);
break;
}
handler--;
i--;
}
}
et1.setText(Double.toString(total4));
resettext = 1;
}

Answer 1

Following your result() method, total4 is set to 0.0 at the beginning, and no code ever changes it when the "." operator is encountered.
The bug is that you are treating "." as an operator. Have special code in your parsing loop to treat it as part of the number. You need to change the line if (!Character.isDigit(c)) {, and handle the maths logic.

Answer 2

If you are not required to implement any specific algorithm then you can use:
ScriptEngineManager manager = new ScriptEngineManager();
ScriptEngine engine = manager.getEngineByName("js");
Object result = engine.eval("3+4");
Otherwise you may want to look at the following:
Shunting Yard Algorithm