What are enums and why are they useful?

Question

Today I was browsing through some questions on this site and I found a mention of an enum being used in singleton pattern about purported thread safety benefits

Answer 1

As for me to make the code readable in future the most useful aplyable case of enumeration is represented in next snippet:

public enum Items {
    MESSAGES, CHATS, CITY_ONLINE, FRIENDS, PROFILE, SETTINGS, PEOPLE_SEARCH, CREATE_CHAT
}

@Override
public boolean onCreateOptionsMenu(Menu menuPrm) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menuPrm);
    View itemChooserLcl;
    for (int i = 0; i < menuPrm.size(); i++) {
        MenuItem itemLcl  = menuPrm.getItem(i);
            itemChooserLcl = itemLcl.getActionView();
            if (itemChooserLcl != null) {
                 //here Im marking each View' tag by enume values:
                itemChooserLcl.setTag(Items.values()[i]);
                itemChooserLcl.setOnClickListener(drawerMenuListener);
            }
        }
    return true;
}
private View.OnClickListener drawerMenuListener=new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        Items tagLcl= (Items) v.getTag();
        switch (tagLcl){
            case MESSAGES: ;
            break;
            case CHATS : ;
            break;
            case CITY_ONLINE : ;
            break;
            case FRIENDS : ;
            break;
            case  PROFILE: ;
            break;
            case  SETTINGS: ;
            break;
            case  PEOPLE_SEARCH: ;
            break;
            case  CREATE_CHAT: ;
            break;
        }
    }
};