FindAngleActivity.java

public class MainActivity extends AppCompatActivity {

    @BindView(R.id.editTextHour)
    EditText editTextHour;

    @BindView(R.id.editTextMinute)
    EditText editTextMinute;

    @BindView(R.id.textViewOutput)
    TextView textViewOutput;

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

        ButterKnife.bind(this);



    }
    @OnClick(R.id.buttonFindAngle)
    public void findAngle(View view){
        String strHour=editTextHour.getText().toString().trim();
        String strMinute=editTextMinute.getText().toString().trim();

        double hour;
        double min;

        if(TextUtils.isEmpty(strHour)){
            editTextHour.setError("Please enter hour");
            return;
        }else{
            hour=Double.parseDouble(editTextHour.getText().toString().trim());
            if(hour <0 || hour >12 ){
                editTextHour.setError("Hour must be between 1 to 12");
                return;
            }
        }

        if(TextUtils.isEmpty(strMinute)){
            editTextMinute.setError("Please enter Minutes");
            return;
        }else{
             min=Double.parseDouble(editTextMinute.getText().toString().trim());
            if(min <0 || min >60 ){
                editTextMinute.setError("Minute must be between 1 to 60");
                return;
            }
        }


        int angle=calculateAngle(hour, min);
        textViewOutput.setText("Angle between hour and minute: "+String.valueOf(angle));
    }

    // method for calculating the angle between hour and minute
    private int calculateAngle(double hour, double minute) {
        //base condition
        if(hour==12) hour=0;
        if(minute==60) minute=0;

        //Based on 12 hour refrence, then calculate the angle

        double hourAngle=0.5*(60*hour+minute);
        double minuteAngle=6*minute;

        //find the angle between two angle
        int diffAngle=(int)(Math.abs(hourAngle-minuteAngle));

        // return the smallest angle between two possible angles
        return minimumPossibleAngle(360-diffAngle, diffAngle);

    }

    // find the minimum angle 
    private int minimumPossibleAngle(int maxAngle, int minAngle) {
        return (maxAngle<minAngle) ? maxAngle:minAngle;
    }
}