JsonScope

因为写JsonReader和JsonWriter的时候有依赖，为了便于说明问题。单独把JsonScope列出来，请大家理解哈。
从这些常量，我们可以简单的理解下Gson设计思想的一些方面，比如，逻辑层次、颗粒度等

随着大家编码经验越来越多，相信很多人已经认识到了颗粒度划分和层次划分的重要，这行能力对大家转型做设计（架构师）具有很大的意义。

EMPTY_DOCUMENT 和 NONEMPTY_DOCUMENT  文档
EMPTY_ARRAY   和   NONEMPTY_ARRAY    数珠
EMPTY_OBJECT  和   NONEMPTY_OBJECT。 对象（和map类似，所有的值都是key-value的形式），先输出key（name）然后才输出value，所以需要增加一个常量DANGLING_NAME
CLOSED所有操作结束后变成close状态，不能够再做任何操作
/**
 * Lexical scoping elements within a JSON reader or writer.
 *
 * @author Jesse Wilson
 * @since 1.6
 */
final class JsonScope {

    /**
     * An array with no elements requires no separators or newlines before
     * it is closed.
     */
    static final int EMPTY_ARRAY = 1;

    /**
     * A array with at least one value requires a comma and newline before
     * the next element.
     */
    static final int NONEMPTY_ARRAY = 2;

    /**
     * An object with no name/value pairs requires no separators or newlines
     * before it is closed.
     */
    static final int EMPTY_OBJECT = 3;

    /**
     * An object whose most recent element is a key. The next element must
     * be a value.
     */
    static final int DANGLING_NAME = 4;

    /**
     * An object with at least one name/value pair requires a comma and
     * newline before the next element.
     */
    static final int NONEMPTY_OBJECT = 5;

    /**
     * No object or array has been started.
     */
    static final int EMPTY_DOCUMENT = 6;

    /**
     * A document with at an array or object.
     */
    static final int NONEMPTY_DOCUMENT = 7;

    /**
     * A document that's been closed and cannot be accessed.
     */
    static final int CLOSED = 8;
}