单例设计模式,保证工厂对象唯一
内存缓存数组,保证产品对象唯一

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public class FragmentFactory {

    private static Map<Integer,Fragment> sFragmentCache = new HashMap<>();

    private FragmentFactory() {
    }

    private static FragmentFactory sFragmentFactory;

    public FragmentFactory getInstance(){
        if(sFragmentFactory == null){
            sFragmentFactory = new FragmentFactory();
        }
        return sFragmentFactory;
    }

    public static Fragment createFragment(int position){
        //优先读取历史保存的fragment
        if(sFragmentCache.containsKey(position)){
            return sFragmentCache.get(position);
        }

        Fragment fragment;
        switch (position){
            case 0:
                fragment = new HomeFragment();
                break;
            case 1:
                fragment = new AppFragment();
                break;
            case 2:
                fragment = new GameFragment();
                break;
            default:
                fragment = new OtherFragment();
                break;
        }
        sFragmentCache.put(position,fragment);
        return fragment;
    }

}