public void back() throws JSONException {
        if (this.usePrevious || this.index <= 0) {
            throw new JSONException("Stepping back two steps is not supported");
        }
        this.index -= 1;
        this.character -= 1;
        this.usePrevious = true;
        this.eof = false;
    }
@author Robert HG (254963746@qq.com) on 12/28/15.
lts-core/src/main/java/com/github/ltsopensource/json/JSONTokenizer.java