public class MainActivity extends AppCompatActivity
    implements View.OnClickListener {

    TextView tv1,tv2;

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

        tv1=(TextView) findViewById(R.id.calculo);
        tv2=(TextView) findViewById(R.id.resultado);
        tv1.setText("");
        tv2.setText("");

        View bt1 = findViewById(R.id.boton1);
        bt1.setOnClickListener(this);

        View bt2 = findViewById(R.id.boton2);
        bt2.setOnClickListener(this);

        View bt3 = findViewById(R.id.boton3);
        bt3.setOnClickListener(this);

        View bt4 = findViewById(R.id.boton4);
        bt4.setOnClickListener(this);

        View bt5 = findViewById(R.id.boton5);
        bt5.setOnClickListener(this);

        View bt6 = findViewById(R.id.boton6);
        bt6.setOnClickListener(this);

        View bt7 = findViewById(R.id.boton7);
        bt7.setOnClickListener(this);

        View bt8 = findViewById(R.id.boton8);
        bt8.setOnClickListener(this);

        View bt9 = findViewById(R.id.boton9);
        bt9.setOnClickListener(this);

        View bt0 = findViewById(R.id.boton0);
        bt0.setOnClickListener(this);

        View btPunto = findViewById(R.id.botonPunto);
        btPunto.setOnClickListener(this);

        View btIgual = findViewById(R.id.botonIgual);
        btIgual.setOnClickListener(this);

        View btSuma = findViewById(R.id.botonSuma);
        btSuma.setOnClickListener(this);

        View btResta = findViewById(R.id.botonResta);
        btResta.setOnClickListener(this);

        View btMultiplica = findViewById(R.id.multiplica);
        btMultiplica.setOnClickListener(this);

        View btDivide = findViewById(R.id.botonDivide);
        btDivide.setOnClickListener(this);

        View btLimpia = findViewById(R.id.botonLimpia);
        btLimpia.setOnClickListener(this);
    }

    double resul, m1=0,m2=0;
    char op1='+';

    public void onClick(View tv){
        if(tv.getId()== R.id.boton1)
            tv1.append("1");
        else if (tv.getId()==R.id.boton2)
            tv1.append("2");
        else if (tv.getId()==R.id.boton3)
            tv1.append("3");
        else if (tv.getId()==R.id.boton4)
            tv1.append("4");
        else if (tv.getId()==R.id.boton5)
            tv1.append("5");
        else if (tv.getId()==R.id.boton6)
            tv1.append("6");
        else if (tv.getId()==R.id.boton7)
            tv1.append("7");
        else if (tv.getId()==R.id.boton8)
            tv1.append("8");
        else if (tv.getId()==R.id.boton9)
            tv1.append("9");
        else if (tv.getId()==R.id.boton0)
            tv1.append("0");
        else if (tv.getId()==R.id.botonPunto)
            tv1.append(".");
        else if (tv.getId()==R.id.botonLimpia) {
            tv1.setText("");
            tv2.setText("0");
            m1=0;
            op1='+';
        }
        else if (tv.getId()==R.id.botonSuma) {
            calcular('+');
        }
        else if (tv.getId()==R.id.botonResta) {
           calcular('-');
        }
        else if (tv.getId()==R.id.multiplica) {

            calcular('x');
        }
        else if (tv.getId()==R.id.botonDivide){

            calcular('/');
        }
        else if (tv.getId()==R.id.botonIgual)
            calcular('=');
    }

    public void calcular (char op){
        resul=m1;
        String cadena =tv1.getText().toString();
        try {
            m2 = Double.parseDouble(cadena);
            if (op1 == '+')
                resul = m1 + m2;
            else if (op1 == '-')
                resul = m1 + m2;
            else if (op1 == 'x')
                resul = m1 * m2;
            else if (op1 == '/')
                resul = m1 / m2;
            m1 = resul;
            op1 = op;

            if (op == '=') {
                tv1.setText("" + m1);
                tv2.setText("" + m1 + op1);
            }
            else {
                tv1.setText("");
                tv2.setText(""+m1+op1);
            }
        }
        catch(NumberFormatException nfe)
        {
            Toast.makeText(this,"Numero Incorrecto",Toast.LENGTH_LONG).show();
        }

    }
}