ActivityMain

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

import java.text.DecimalFormat;



public class MainActivity extends AppCompatActivity {



    private static final char ADDITION = '+';
    private static final char SUBTRACTION = '-';
    private static final char MULTIPLICATION = '*';
    private static final char DIVISION = '/';

    private char CURRENT_ACTION;

    private double valueOne = Double.NaN;
    private double valueTwo;

    private DecimalFormat decimalFormat;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        decimalFormat = new DecimalFormat("#.##########");

        Button buttonDot = (Button) findViewById(R.id.buttonDot);
        Button buttonZero = (Button) findViewById(R.id.buttonZero);
        Button buttonOne = (Button) findViewById(R.id.buttonOne);
        Button buttonTwo = (Button) findViewById(R.id.buttonTwo);
        Button buttonThree = (Button) findViewById(R.id.buttonThree);
        Button buttonFour = (Button) findViewById(R.id.buttonFour);
        Button buttonFive = (Button) findViewById(R.id.buttonFive);
        Button buttonSix = (Button) findViewById(R.id.buttonSix);
        Button buttonSeven = (Button) findViewById(R.id.buttonSeven);
        Button buttonEight = (Button) findViewById(R.id.buttonEight);
        Button buttonNine = (Button) findViewById(R.id.buttonNine);
        Button buttonAdd = (Button) findViewById(R.id.buttonAdd);
        Button buttonSubtract = (Button) findViewById(R.id.buttonSubtract);
        Button buttonMultiply = (Button) findViewById(R.id.buttonMultiply);
        Button buttonDivide = (Button) findViewById(R.id.buttonDivide);
        Button buttonClear = (Button) findViewById(R.id.buttonClear);
        Button buttonEqual = (Button) findViewById(R.id.buttonEqual);

        final EditText editText = (EditText) findViewById(R.id.editText);
        final TextView infoTextView = (TextView) findViewById(R.id.infoTextView);

        buttonDot.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                editText.setText(editText.getText() + ".");
            }
        });

        buttonZero.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                editText.setText(editText.getText() + "0");
            }
        });

        buttonOne.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
               editText.setText(editText.getText() + "1");
            }
        });

        buttonTwo.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                editText.setText(editText.getText() + "2");
            }
        });

        buttonThree.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                editText.setText(editText.getText() + "3");
            }
        });

        buttonFour.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                editText.setText(editText.getText() + "4");
            }
        });

        buttonFive.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                editText.setText(editText.getText() + "5");
            }
        });

        buttonSix.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                editText.setText(editText.getText() + "6");
            }
        });

        buttonSeven.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                editText.setText(editText.getText() + "7");
            }
        });

        buttonEight.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                editText.setText(editText.getText() + "8");
            }
        });

        buttonNine.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                editText.setText(editText.getText() + "9");
            }
        });

        buttonAdd.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                computeCalculation();
                CURRENT_ACTION = ADDITION;
                infoTextView.setText(decimalFormat.format(valueOne) + "+");
                editText.setText(null);
            }
        });

       buttonSubtract.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                computeCalculation();
                CURRENT_ACTION = SUBTRACTION;
               infoTextView.setText(decimalFormat.format(valueOne) + "-");
                editText.setText(null);
            }
        });

       buttonMultiply.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                computeCalculation();
                CURRENT_ACTION = MULTIPLICATION;
                infoTextView.setText(decimalFormat.format(valueOne) + "*");
                editText.setText(null);
            }
        });

        buttonDivide.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                computeCalculation();
                CURRENT_ACTION = DIVISION;
                infoTextView.setText(decimalFormat.format(valueOne) + "/");
                editText.setText(null);
            }
        });

        buttonEqual.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                computeCalculation();
               infoTextView.setText(infoTextView.getText().toString() +
                        decimalFormat.format(valueTwo) + " = " + decimalFormat.format(valueOne));
                valueOne = Double.NaN;
                CURRENT_ACTION = '0';
            }
        });

        buttonClear.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                if(editText.getText().length() > 0) {
                    CharSequence currentText = editText.getText();
                   editText.setText(currentText.subSequence(0, currentText.length()-1));
                }
                else {
                    valueOne = Double.NaN;
                    valueTwo = Double.NaN;
                    editText.setText("");
                    infoTextView.setText("");
                }
            }
        });
    }

    private void computeCalculation() {
        if(!Double.isNaN(valueOne)) {
            EditText editText = (EditText) findViewById(R.id.editText);
            valueTwo = Double.parseDouble(editText.getText().toString());
            editText.setText(null);

            if(CURRENT_ACTION == ADDITION)
                valueOne = this.valueOne + valueTwo;
            else if(CURRENT_ACTION == SUBTRACTION)
                valueOne = this.valueOne - valueTwo;
            else if(CURRENT_ACTION == MULTIPLICATION)
                valueOne = this.valueOne * valueTwo;
            else if(CURRENT_ACTION == DIVISION)
                valueOne = this.valueOne / valueTwo;
        }
        else {
            try {
                EditText editText = (EditText) findViewById(R.id.editText);//potential
                valueOne = Double.parseDouble(editText.getText().toString());
            }
            catch (Exception e){}
        }


    }
    private void showIn2(){
        EditText editText = (EditText) findViewById(R.id.editText);
        valueTwo = Double.parseDouble(editText.getText().toString());

        editText.setText(null);



        editText.setText(Integer.toString((int) valueTwo,2));



    }
}