Fragment

package com.example.fragment;

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

import android.os.Bundle;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity {

    Button fb1,fb2;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        fb1=findViewById(R.id.fbt);
        fb2=findViewById(R.id.fbt2);
        final Fragment first= new AboutFragment();
        final Fragment second= new MessageFragment();
        fb1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                FragmentManager fm=getSupportFragmentManager();
                FragmentTransaction fragmentTransaction=fm.beginTransaction();
                fragmentTransaction.replace(R.id.layout,first);
                fragmentTransaction.commit();
            }
        });
        fb2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

                FragmentManager fm=getSupportFragmentManager();
                FragmentTransaction fragmentTransaction=fm.beginTransaction();
                fragmentTransaction.replace(R.id.layout,second);
                fragmentTransaction.commit();
            }
        });

    }
}