为什么Android使用Ints而不是Enums

Question

阅读关于Android,我可以看到使用这个框架的许多部分int常量返回值,或配置值(也喜欢在这里的START_REDELIVER_INTENT),而不是一个enum,这是据我所知是可以找到的原因有很多更好的选择在网络上,像这样.

所以这让我想知道......为什么Google决定使用这么多int's而不是enum's？

Answer 1

从文档中直接拉出来

Enums often require more than twice as much memory as static constants. You should strictly avoid using enums on Android.

http://developer.android.com/training/articles/memory.html#Overhead

编辑:

也是罗曼盖伊谈话之一的幻灯片

https://speakerdeck.com/romainguy/android-memories?slide=67

Answer 2

int上的操作比枚举上的操作快许多倍.

为自己判断.每次创建枚举时,您都要创建一个至少:

1) Class-loader for it. 
2) You keep this object in memory. 
3) Since enum is static anonymous class - it will always hang in your memory (sometimes even after you close the application.) 

关于Service.在这个类中,标志主要用于比较并将结果返回给上面的类(ContextWrapper).但基本上,如果你深入研究Android SDK的内容,你会发现自己几乎所有这些标志都用于通过轮换操作.

即使在Java中也使用JDK中的二进制移位操作:

/**
 * Max capacity for a HashMap. Must be a power of two >= MINIMUM_CAPACITY.
 */
private static final int MAXIMUM_CAPACITY = 1 << 30;

您也可以在Android SDK中查看Window类

/**
 * Set the container for this window.  If not set, the DecorWindow
 * operates as a top-level window; otherwise, it negotiates with the
 * container to display itself appropriately.
 *
 * @param container The desired containing Window.
 */
public void setContainer(Window container) {
    mContainer = container;
    if (container != null) {
        // Embedded screens never have a title.
        mFeatures |= 1<<FEATURE_NO_TITLE;
        mLocalFeatures |= 1<<FEATURE_NO_TITLE;
        container.mHasChildren = true;
    }
}

/** The default features enabled */
@SuppressWarnings({"PointlessBitwiseExpression"})
protected static final int DEFAULT_FEATURES = (1 << FEATURE_OPTIONS_PANEL) |
        (1 << FEATURE_CONTEXT_MENU);

所以理由是两个(至少):

• 减少内存消耗.

• 由于按位操作,工作速度更快.