Temperature.java

package com.example.dave.temperatureconverter;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    Spinner spinnerInputUnit;
    EditText txtInput;
    TextView resultCelcius;
    TextView resultFaren;
    TextView resultKelvin;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        spinnerInputUnit = (Spinner) findViewById(R.id.spinnerInputUnit);
        ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this,
                R.array.units_array, android.R.layout.simple_spinner_item);
        adapter.setDropDownViewResource(R.layout.support_simple_spinner_dropdown_item);
        spinnerInputUnit.setAdapter(adapter);

        txtInput = (EditText) findViewById(R.id.txtInput);
        resultCelcius = (TextView) findViewById(R.id.resultCelcius);
        resultFaren = (TextView) findViewById(R.id.resultFaren);
        resultKelvin = (TextView) findViewById(R.id.resultKelvin);
    }

    public void convert(View v) {
        double inputValue = Double.valueOf(txtInput.getText().toString());
        String inputUnit = spinnerInputUnit.getSelectedItem().toString();

        switch(inputUnit) {
            case "Celcius":
                resultCelcius.setText(Double.toString(inputValue));
                resultFaren.setText(Double.toString(inputValue * 1.8 + 32));
                resultKelvin.setText(Double.toString(inputValue + 273.15));
                break;
            case "Farenheit":
                resultCelcius.setText(Double.toString((inputValue -32) * 5 / 9));
                resultFaren.setText(Double.toString(inputValue));
                resultKelvin.setText(Double.toString((inputValue + 459.67) * 5 / 9));
                break;
            case "Kelvin":
                resultCelcius.setText(Double.toString(inputValue - 273.15));
                resultFaren.setText(Double.toString(inputValue * 9 / 5 - 459.67));
                resultKelvin.setText(Double.toString(inputValue));
                break;
        }
    }
}