IntDef 注释

此注释确保仅使用你期望的有效整数常量。
以下示例说明了创建注释的步骤：

import android.support.annotation.IntDef;

public abstract class Car {

    //Define the list of accepted constants
    @IntDef({MICROCAR, CONVERTIBLE, SUPERCAR, MINIVAN, SUV})

    //Tell the compiler not to store annotation data in the .class file
    @Retention(RetentionPolicy.SOURCE)
    //Declare the CarType annotation
    public @interface CarType {}

    //Declare the constants
    public static final int MICROCAR = 0;
    public static final int CONVERTIBLE = 1;
    public static final int SUPERCAR = 2;
    public static final int MINIVAN = 3;
    public static final int SUV = 4;

    @CarType
    private int mType;

    @CarType
    public int getCarType(){
        return mType;
    };

    public void setCarType(@CarType int type){
        mType = type;
    }
}

它们还使代码完成能够自动提供允许的常量。
构建此代码时，如果 type 参数未引用其中一个已定义的常量，则会生成警告。