How to replace one fragment with another with two buttons

Question

I am opening the application and it crashed

Answer 1

You can be write FragmentTransaction inside the onClick of button. Follow below code,

public class MainActivity extends AppCompatActivity {
    Button frag1, frag2;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        frag1 = (Button) findViewById(R.id.frag1btn);
        frag2 = (Button) findViewById(R.id.frag2btn);
        frag1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FragmentTransaction trans = getSupportFragmentManager().beginTransaction();
                trans.replace(R.id.fragment_container, new Fragment1());
                trans.commit();
            }
        });
        frag2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                FragmentTransaction trans = getSupportFragmentManager().beginTransaction();
                trans.replace(R.id.fragment_container, new Fragment2());
                trans.commit();
            }
        });
    }
}