Dagger Android basic classes sample code in Java

ActivityModule.java

import dagger.Module;
import dagger.android.ContributesAndroidInjector;

@Module
public abstract class ActivityModule {
    @ContributesAndroidInjector(modules = {FragmentBuildersModule.class})
    abstract MainActivity contributeMainActivity();
}

AppComponent.java

import android.app.Application;
import javax.inject.Singleton;

import dagger.BindsInstance;
import dagger.Component;
import dagger.android.AndroidInjectionModule;
import dagger.android.support.AndroidSupportInjectionModule;

@Singleton
@Component(modules = {
        AndroidInjectionModule.class,
        AndroidSupportInjectionModule.class,
        AppModule.class,
        ActivityModule.class
})

public interface AppComponent {
    @Component.Builder
    interface Builder {
        @BindsInstance
        AppComponent.Builder application(Application application);

        AppComponent build();
    }

    void inject(MyApplication application);
}

AppInjector.java

import android.app.Activity;
import android.app.Application;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;

import dagger.android.AndroidInjection;
import dagger.android.support.AndroidSupportInjection;
import dagger.android.support.HasSupportFragmentInjector;

public class AppInjector {

    public static void init(MyApplication application) {
        DaggerAppComponent.builder()
                .application(application)
                .build()
                .inject(application);

        application.registerActivityLifecycleCallbacks(new Application.ActivityLifecycleCallbacks() {
            @Override
            public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
                handleActivity(activity); // calledn after Activity's super.onCreate() invoked, so anything in onCreate() is injected.
            }

            @Override
            public void onActivityStarted(Activity activity) {

            }

            @Override
            public void onActivityResumed(Activity activity) {

            }

            @Override
            public void onActivityPaused(Activity activity) {

            }

            @Override
            public void onActivityStopped(Activity activity) {

            }

            @Override
            public void onActivitySaveInstanceState(Activity activity, Bundle outState) {

            }

            @Override
            public void onActivityDestroyed(Activity activity) {

            }
        });


    }

    private static void handleActivity(Activity activity) {
        if (activity instanceof HasSupportFragmentInjector) {
            AndroidInjection.inject(activity);
        }
        if (activity instanceof FragmentActivity) {
            ((FragmentActivity) activity).getSupportFragmentManager()
                    .registerFragmentLifecycleCallbacks(new FragmentManager.FragmentLifecycleCallbacks() {
                        @Override
                        public void onFragmentCreated(FragmentManager fm, Fragment f, Bundle savedInstanceState) {
                            super.onFragmentCreated(fm, f, savedInstanceState);
                            // called after Fragment's onCreate(), so the dependencies are still null in onCreate()
                            // If you need some work in onCreate(), just add an inject() method in component and call it Fragment's onCreate()
                            if (f instanceof Injectable) {
                                AndroidSupportInjection.inject(f);
                            }
                        }
                    }, true);
        }
    }
}

FragmentBuildersModule.java

import dagger.Module;
import dagger.android.ContributesAndroidInjector;

@Module
public abstract class FragmentBuildersModule {
    @ContributesAndroidInjector
    abstract HomeFragment contributeHomeFragment();
}