Calculator App

Main Activity

public class MainActivity extends AppCompatActivity {

    public static final String EXTRA_MESSAGE1="extra_key1";
    public static final String EXTRA_MESSAGE2="extra_key2";

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

    public void oKButton(View view){
        Intent intent=new Intent(this,SecondActivity.class);
        EditText editText1=(EditText)findViewById(R.id.editText);
        EditText editText2=(EditText)findViewById(R.id.editText2);
        String message1=editText1.getText().toString();
        String message2=editText2.getText().toString();
        intent.putExtra(EXTRA_MESSAGE1,message1);
        intent.putExtra(EXTRA_MESSAGE2,message2);
        startActivity(intent);
    }
}

Second Activity

public class SecondActivity extends AppCompatActivity {

    @Override    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);
        Intent intent=getIntent();
        String message1=intent.getStringExtra(MainActivity.EXTRA_MESSAGE1);
        String message2=intent.getStringExtra(MainActivity.EXTRA_MESSAGE2);
        EditText editText3=findViewById(R.id.editText3);
        editText3.setText(message1);
        EditText editText4=findViewById(R.id.editText4);
        editText4.setText(message2);
    }

    public void addition(View view){
        EditText editText3=findViewById(R.id.editText3);
        EditText editText4=findViewById(R.id.editText4);
        String num1=editText3.getText().toString();
        int no1=Integer.parseInt(num1);
        String num2=editText4.getText().toString();
        int no2=Integer.parseInt(num2);
        int result=no1+no2;
        TextView textView=findViewById(R.id.textView5);
        textView.setText(num1+"+"+num2+"="+result);
    }

    public void Substraction(View view){
        EditText editText3=findViewById(R.id.editText3);
        EditText editText4=findViewById(R.id.editText4);
        String num1=editText3.getText().toString();
        int no1=Integer.parseInt(num1);
        String num2=editText4.getText().toString();
        int no2=Integer.parseInt(num2);
        int result=no1-no2;
        TextView textView=findViewById(R.id.textView5);
        textView.setText(num1+"-"+num2+"="+result);
    }

    public void Multiply(View view){
        EditText editText3=findViewById(R.id.editText3);
        EditText editText4=findViewById(R.id.editText4);
        String num1=editText3.getText().toString();
        int no1=Integer.parseInt(num1);
        String num2=editText4.getText().toString();
        int no2=Integer.parseInt(num2);
        int result=no1*no2;
        TextView textView=findViewById(R.id.textView5);
        textView.setText(num1+"*"+num2+"="+result);
    }

    public void division(View view){
        EditText editText3=findViewById(R.id.editText3);
        EditText editText4=findViewById(R.id.editText4);
        String num1=editText3.getText().toString();
        int no1=Integer.parseInt(num1);
        String num2=editText4.getText().toString();
        double no2=Double.parseDouble(num2);
        double result=no1/no2;
        TextView textView=findViewById(R.id.textView5);
        textView.setText(num1+"/"+num2+"="+result);
    }
}