Android Fragment Manager - SDK 16+

FragmentManagerActivity.java

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;

public class MyActivity extends AppCompactActivity {

    private static final String FRAGMENT_ONE = "FRAGMENT_ONE";
    private static final String FRAGMENT_TWO = "FRAGMENT_TWO";
    private String currentFragmentTag;

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

    /* ... */
    
        if (caseOne) {
            swapFragment(MyFragmentOne.class, FRAGMENT_ONE);
        } else if (caseTwo) {
            swapFragment(MyFragmentTwo.class, FRAGMENT_TWO);
        }
    
    /*...*/

    public void swapFragment(Class<? extends Fragment> fragmentClass, String fragmentTag) {
        try {
            FragmentManager fragmentManager = getSupportFragmentManager();
            Fragment fragment = fragmentManager.findFragmentByTag(fragmentTag);
            if (fragment == null) {
                fragmentManager.beginTransaction().add(R.id.fragment_container, fragmentClass.newInstance(), fragmentTag).commit();
            } else {
                fragmentManager.beginTransaction().show(fragment).commit();
            }
            if (currentFragmentTag != null) {
                Fragment currentFragment = fragmentManager.findFragmentByTag(currentFragmentTag);
                if (currentFragment != null) {
                    fragmentManager.beginTransaction().hide(currentFragment).commit();
                }
            }
            currentFragmentTag = fragmentTag;
        } catch (Exception e) {
            Log.e(getClass().getSimpleName(), e.getMessage(), e);
        }
    }
}

layout_myactivity.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/fragment_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />