Can we create new class in MainActivity.java?

Question

How to add another class within this class MainActivity extends AppCompatActivity. If there was this line of code,

public class MainActivity extends AppCompatActivity {
    private EditText Num1;
    private Button btnAdd;

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

        Num1 = (EditText) findViewById(R.id.firstName);
        btnAdd = (Button) findViewById(R.id.btnAdd);
        btnAdd.setOnClickListener(new View.OnClickListener(){
        @Override
            public void onClick(View v) {
                multiLine.setText(Num1.getText().toString()
       });
    }
}

can there be another class where I can call the Num1 value, if so how to pass the EditText value on this new Calculate class. I'm new to Android Studio plus the java so I would appreciate any ideas you have.

public class Calculate {
    private int num = Num1

}

I'm not sure if my question makes sense but I've been trying to pass the Num1 value to the new class I have created. I could be doing it wrong and also I tried creating new class in java but didn't know how to call the values there from MainActivity.java.

Answer 1

You can put any number of classes in a single .java file, even as peers not inner classes. That is typically not done though. It's standard to put each new class in a new .java file.

Answer 2

just put the calculate class above the lowest bottom bracket like this:

public class MainActivity extends AppCompatActivity {
    private EditText Num1;
    private Button btnAdd;

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

        Num1 = (EditText) findViewById(R.id.firstName);
        btnAdd = (Button) findViewById(R.id.btnAdd);
        btnAdd.setOnClickListener(new View.OnClickListener(){
        @Override
            public void onClick(View v) {
                multiLine.setText(Num1.getText().toString()
       });
    }
    public class Calculate {
        private int num;

        public Calculate(int number){
            num = number
        }
    }
}

You can pass the Num1-value via the constructor (or you decide to write a setter-method for it). Use it in the MainActivity like this:
Calculate calc = new Calculate(Num1);