- Simple Android clone of the native iOS Calculator built with Kotlin, using modern architecture and tools:
Custom XML UI mimicking iOS calculator design
Math expression parsing with exp4j
Input handling with Kotlin Regex
LiveData for reactive state updates
🧩 Libraries & Utilities
🔢 exp4j by André Rouél – Lightweight Java library for evaluating mathematical expressions. Used for parsing calculator input.
🧠 LiveData – For reactive UI updates 🔍 Kotlin Regex – For input filtering & validation
📦 Dependency (for gradle)
implementation("net.objecthunter:exp4j:0.4.8")🧮 Example to use
import net.objecthunter.exp4j.ExpressionBuilder
val expression = ExpressionBuilder("2 + 3 * (7 - 1)").build()
val result = expression.evaluate()
println("Result: $result") // Output: Result: 20.0✅ My Usage
fun calculate(expression: String): String {
var calcResult: String = ""
try {
var expr = ExpressionBuilder(expression).build().evaluate()
calcResult = when {
expr.isNaN() || expr.isInfinite() -> "Undefined"
expr % 1 == 0.0 -> expr.toInt().toString()
expr % 1 > 0.0 -> String.format("%.3f", expr)
else -> expr.toString()
}
} catch (e: ArithmeticException) {
calcResult = "Undefined"
} catch (e: Exception) {
calcResult = "Invalid"
}
return calcResult
}