枚举

枚举用法：
1.okhttp

package okhttp3;

import java.io.IOException;

public enum Protocol
{
  HTTP_1_0, HTTP_1_1, SPDY_3, HTTP_2;

  private final String protocol;

  public static Protocol get(String protocol)
    throws IOException
  {
    if (protocol.equals(HTTP_1_0.protocol)) return HTTP_1_0;
    if (protocol.equals(HTTP_1_1.protocol)) return HTTP_1_1;
    if (protocol.equals(HTTP_2.protocol)) return HTTP_2;
    if (protocol.equals(SPDY_3.protocol)) return SPDY_3;
    throw new IOException("Unexpected protocol: " + protocol);
  }

  public String toString()
  {
    return this.protocol;
  }
}

2.oschina

package net.oschina.app.ui;

import net.oschina.app.R;
import net.oschina.app.fragment.ExploreFragment;
import net.oschina.app.fragment.MyInformationFragment;
import net.oschina.app.viewpagerfragment.NewsViewPagerFragment;
import net.oschina.app.viewpagerfragment.TweetsViewPagerFragment;

public enum MainTab {

    NEWS(0, R.string.main_tab_name_news, R.drawable.tab_icon_new,
            NewsViewPagerFragment.class),

    TWEET(1, R.string.main_tab_name_tweet, R.drawable.tab_icon_tweet,
            TweetsViewPagerFragment.class),

    QUICK(2, R.string.main_tab_name_quick, R.drawable.tab_icon_new,
            null),

    EXPLORE(3, R.string.main_tab_name_explore, R.drawable.tab_icon_explore,
            ExploreFragment.class),

    ME(4, R.string.main_tab_name_my, R.drawable.tab_icon_me,
            MyInformationFragment.class);

    private int idx;
    private int resName;
    private int resIcon;
    private Class<?> clz;

    private MainTab(int idx, int resName, int resIcon, Class<?> clz) {
        this.idx = idx;
        this.resName = resName;
        this.resIcon = resIcon;
        this.clz = clz;
    }

    public int getIdx() {
        return idx;
    }

    public void setIdx(int idx) {
        this.idx = idx;
    }

    public int getResName() {
        return resName;
    }

    public void setResName(int resName) {
        this.resName = resName;
    }

    public int getResIcon() {
        return resIcon;
    }

    public void setResIcon(int resIcon) {
        this.resIcon = resIcon;
    }

    public Class<?> getClz() {
        return clz;
    }

    public void setClz(Class<?> clz) {
        this.clz = clz;
    }
}

private void initTabs() {
        MainTab[] tabs = MainTab.values();
        final int size = tabs.length;
        for (int i = 0; i < size; i++) {
            MainTab mainTab = tabs[i];
            TabSpec tab = mTabHost.newTabSpec(getString(mainTab.getResName()));
            View indicator = LayoutInflater.from(getApplicationContext())
                    .inflate(R.layout.tab_indicator, null);
            TextView title = (TextView) indicator.findViewById(R.id.tab_title);
            Drawable drawable = this.getResources().getDrawable(
                    mainTab.getResIcon());
            title.setCompoundDrawablesWithIntrinsicBounds(null, drawable, null,
                    null);
            if (i == 2) {
                indicator.setVisibility(View.INVISIBLE);
                mTabHost.setNoTabChangedTag(getString(mainTab.getResName()));
            }
            title.setText(getString(mainTab.getResName()));
            tab.setIndicator(indicator);
            tab.setContent(new TabContentFactory() {

                @Override
                public View createTabContent(String tag) {
                    return new View(MainActivity.this);
                }
            });
            mTabHost.addTab(tab, mainTab.getClz(), null);

            if (mainTab.equals(MainTab.ME)) {
                View cn = indicator.findViewById(R.id.tab_mes);
                mBvNotice = new BadgeView(MainActivity.this, cn);
                mBvNotice.setBadgePosition(BadgeView.POSITION_TOP_RIGHT);
                mBvNotice.setTextSize(TypedValue.COMPLEX_UNIT_SP, 10);
                mBvNotice.setBackgroundResource(R.drawable.notification_bg);
                mBvNotice.setGravity(Gravity.CENTER);
            }
            mTabHost.getTabWidget().getChildAt(i).setOnTouchListener(this);
        }
    }

枚举很像c里面的结构体，小巧。可以保存信息。保存tabhost的模板信息。
枚举可以替代以前在接口里面定义的常量字符串。不用public static final了。
枚举可以switch。