完整代码如下;

package com.example.fragmenttest;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentTransaction;

import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    private static final String TAG = "MainActivity";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        Button button = findViewById(R.id.btn);
        button.setOnClickListener(v->{

            replaceFragment(new AnotherRightFragment());
        });


        replaceFragment(new RightFragment());

        Fragment fragmentById = getSupportFragmentManager().findFragmentById(R.id.right_fragment);
        Log.d(TAG, "onCreate: ");
    }

    private void replaceFragment(Fragment fragment) {


        FragmentManager supportFragmentManager = getSupportFragmentManager();

        FragmentTransaction fragmentTransaction = supportFragmentManager.beginTransaction();

        fragmentTransaction.addToBackStack(null);//添加到后退栈
        fragmentTransaction.replace(R.id.right_layout,fragment);
        fragmentTransaction.commit();


    }
}

RightLayout:

package com.example.fragmenttest;

import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

public class RightFragment extends Fragment {

    private static final String TAG = "RightFragment";

    @Nullable

    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {


        View view = inflater.inflate(R.layout.right_fragment, container, false);
        return view;


    }


    public void test(){
        Log.d(TAG, "test: ");
    }
}

你在哪里创建的fragment呀？