Build.VERSION.SDK_INT ＜ Build.VERSION_CODES.O的含义

1、VERSION和VERSION_CODES的理解

VERSION是当前系统版本
VERSION_CODES是现有系统版本
根据下述代码，标题中Build.VERSION.SDK_INT ＜ Build.VERSION_CODES.O的含义即为，当前安卓系统版本小于安卓8.0的情况。

    public static class VERSION_CODES {
        public static final int BASE = 1;
        public static final int BASE_1_1 = 2;
        public static final int CUPCAKE = 3;
        public static final int CUR_DEVELOPMENT = 10000;
        public static final int DONUT = 4;
        public static final int ECLAIR = 5;
        public static final int ECLAIR_0_1 = 6;
        public static final int ECLAIR_MR1 = 7;
        public static final int FROYO = 8;
        public static final int GINGERBREAD = 9;
        public static final int GINGERBREAD_MR1 = 10;
        public static final int HONEYCOMB = 11;
        public static final int HONEYCOMB_MR1 = 12;
        public static final int HONEYCOMB_MR2 = 13;
        public static final int ICE_CREAM_SANDWICH = 14;
        public static final int ICE_CREAM_SANDWICH_MR1 = 15;
        public static final int JELLY_BEAN = 16;
        public static final int JELLY_BEAN_MR1 = 17;
        public static final int JELLY_BEAN_MR2 = 18;
        public static final int KITKAT = 19;
        public static final int KITKAT_WATCH = 20;
        public static final int LOLLIPOP = 21;
        public static final int LOLLIPOP_MR1 = 22;
        public static final int M = 23;
        public static final int N = 24;
        public static final int N_MR1 = 25;
        public static final int O = 26;
        public static final int O_MR1 = 27;
        public static final int P = 28;
        public static final int Q = 29;

        public VERSION_CODES() {
            throw new RuntimeException("Stub!");
        }
    }

    public static class VERSION {
        public static final String BASE_OS = null;
        public static final String CODENAME = null;
        public static final String INCREMENTAL = null;
        public static final int PREVIEW_SDK_INT = 0;
        public static final String RELEASE = null;
        /** @deprecated */
        @Deprecated
        public static final String SDK = null;
        public static final int SDK_INT = 0;
        public static final String SECURITY_PATCH = null;

        public VERSION() {
            throw new RuntimeException("Stub!");
        }
    }

2、安卓系统版本和安卓api版本关系列表

Android版本	Android API	代号	发布年份
Android12	31	无	还没正式发布
Android11	30	无	2020
Android10	29	Q	2019
Android9	28	Pie	2018
Android8.1	27	Oreo	2017
Android8.0	26	Oreo	2017
Android7.1/Android7.1.1/Android7.1.2	25	Nougat	2016
Android7.0	24	Nougat	2016
Android6.0/Android6.0.1	23	Marshmallow	2015
Android5.1/Android5.1.1	22	Lollipop	2015
Android5.0	21	Lollipop	2014
Android4.4W	20	KitKat	2014
Android4.4	19	KitKat	2013
Android4.3	18	Jelly Bean	2013
Android4.2	17	Jelly Bean	2012
Android4.1	16	Jelly Bean	2012

依据：https://en.wikipedia.org/wiki/Android_version_history