import java.util.HashMap;
import java.util.Map;

/**
 * @descrition 枚舉
 * @since 2020-05-21 18:00
 */
public class EnumInterface {
    String TYPE_FACE = "face";
    String TYPE_HUMAN_BODY = "humanBody";
    String TYPE_MOTOR_VEHICLE = "motorVehicle";
    String TYPE_NON_MOTOR_VEHICLE = "nonMotorVehicle";

    // 人臉特征
    String[] faceCharacteristics = new String[]
            {"Gender", "Hat", "Glass", "Mask"};

    // 人體特征
    String[] humanBodyCharacteristics = new String[]
            {"SleeveStyle", "UpperColor", "UpperTexture", "LowerType", "LowerColor", "ShoesStyle", "ShoesColor",
                    "HairStyle", "Bag", "Appendix", "AgeRange", "HumanBodyGender"};

    // 機動車特征
    String[] motorVehicleCharacteristics = new String[]
            {"PlateText", "VehicleClass", "VehicleColor", "VehicleHead", "PlateClass",
                    "PlateColor", "PlateState", "VehicleRoofItem", "VehicleFrontItem", "FaceCoveredItem", "SpecialVehicle"};

    // 非機動車特征
    String[] nonMotorVehicleCharacteristics = new String[]
            {"VehicleType", "VehicleColor", "VehicleHead", "IllegalPassenger", "Gender", "UpperStyle", "UpperColor", "Headwear", "PackStyle"};

    Map<String, String[]> search = new HashMap<String, String[]>() {
        {
            put(TYPE_FACE, faceCharacteristics);
            put(TYPE_HUMAN_BODY, humanBodyCharacteristics);
            put(TYPE_MOTOR_VEHICLE, motorVehicleCharacteristics);
            put(TYPE_NON_MOTOR_VEHICLE, nonMotorVehicleCharacteristics);
        }
    };

}

這里的雙括號”{{}}”用來初始化，使代碼簡潔易讀。
第一層括弧實際是定義了一個匿名內(nèi)部類 (Anonymous Inner Class)，第二層括弧實際上是一個實例初始化塊 (instance initializer block)，這個塊在內(nèi)部匿名類構(gòu)造時被執(zhí)行。
同理，list也可這樣賦值：

private List<String> list = new ArrayList<String>() {
        {
            add("tom");
            add("jerry");
            add("hkj");
        }
    };