How do I call one method of an activity from another class

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Java

Android

this is my activity class,

public class StatusActivity extends AppCompatActivity {


    private boolean cFlag = false;

    public boolean getFlag() { return cFlag;  }

    public void setFlag(boolean cFlag) {
        this.cFlag = cFlag;
    }

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.list);
        adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, 
                                      android.R.id.text1, messages);
        ListView listView = findViewById(android.R.id.list);
        listView.setAdapter(adapter);
        adapters.add(adapter);


        Button btn = findViewById(R.id.btnCustomerCheckIn);
        btn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                setFlag(true);
                cFlag = getFlag();


                Intent intent = new Intent(StatusActivity.this, MainActivity.class);
                Toast.makeText(StatusActivity.this, "customer checked in", 
                                Toast.LENGTH_LONG).show();
                startActivity(intent);
            }
        });


    }

this is a part of another class named as position

public class Position {
    StatusActivity statusactivity = new StatusActivity();
    public  boolean ccflag = statusactivity.getFlag();
    statusactivity.setFlag(false);

    }

What I have tried:

when i am calling

statusactivity.setFlag(false);

it is showing an error. couldn't recognize that what is the error that i am getting. but

statusactivity.getFlag(); 

is working properly. any help is appreciated