public class MainActivity extends AppCompatActivity implements View.OnClickListener {
    private Button plus;
    private Button minus;
    private Button umnogenie;
    private Button delenie;
    private TextView text1;
    private EditText vvod1;
    private EditText vvod2;
    private  double a,b;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        this.setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
        plus = (Button) findViewById(R.id.button9);
        minus= (Button) findViewById(R.id.button10);
        delenie= (Button) findViewById(R.id.button11);
        umnogenie= (Button) findViewById(R.id.button12);
        text1= (TextView) findViewById(R.id.textView);
        vvod1= (EditText) findViewById(R.id.editText);
        vvod2= (EditText) findViewById(R.id.editText2);

        plus.setOnClickListener(this);
        minus.setOnClickListener(this);
        delenie.setOnClickListener(this);
        umnogenie.setOnClickListener(this);

        vvod1.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }



            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                if (s == null)
                    a= 0;
                else
                    a = Integer.parseInt(s.toString());
            }


            @Override
            public void afterTextChanged(Editable s) {

            }
        });
        vvod2.addTextChangedListener(new TextWatcher() {
            @Override
            public void beforeTextChanged(CharSequence s, int start, int count, int after) {

            }

            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                if (s == null)
                    b= 0;
                else
                    b = Integer.parseInt(s.toString());
                }

            @Override
            public void afterTextChanged(Editable s) {

            }
        });

    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){

            case R.id.button9: text1.setText(String.valueOf(a+b));
                break;
            case R.id.button10: text1.setText(String.valueOf(a-b));
                break;
            case R.id.button11: text1.setText(String.valueOf(a/b));
                break;
            case R.id.button12: text1.setText(String.valueOf(a*b));
                break;
        }
    }
}