Single-dose and Multiple-dose X842 Phase 1 Study

Inclusion Criteria: 1. Those aged 18-45 years old (inclusive the upper and lower limits). 2. Body weight of ≥ 50kg for male and ≥ 45kg for female , with a body mass index (BMI) of 19.0-26.0 kg/m2 (inclusive the upper and lower limits, BMI = weight (kg) / height (m) 2). 3. Understand and able to give written informed consent form for participation in this study voluntarily. Those who fail to meet any of the above conditions shall not be enrolled. Exclusion Criteria: Those who meet any of the following conditions shall not be enrolled: 1. History of any clinically significant disease or disorder in cardiovascular system, respiratory system, digestive system, endocrine system, nervous/mental system, blood and lymphatic system, and musculoskeletal system according to the investigator. 2. Comprehensive physical examination, vital signs, laboratory test, 12-lead ECG, or chest X-ray examination (anteroposterior and lateral view) suggests that there are abnormalities that are determined by the investigator to be clinically significant. 3. Those who received helicobacter pylori eradication therapy within 6 months prior to the study drug administration; 4. The results of helicobacter pylori screening (C-14 urea breath test) is positive; 5. Any positive result for hepatitis B surface antigen (HBsAg), hepatitis B e antigen (HBeAg), hepatitis C virus (HCV) antibody, human immunodeficiency virus (HIV), or Treponema pallidum antibody (TP-Ab). 6. History of any food or drug allergy, or any other history of allergic disease (such as asthma, urticaria, and eczematous dermatitis, etc.) considered as clinical significant by the investigator. 7. Subjects who had taken any drug within 2 weeks prior to screening, which may affect the results of the study according to the investigator. 8. History of drug abuse within 12 months prior to screening or positive urine drug result at screening. 9. Those who regularly drink alcohol within 6 months prior to screening, that is, more than 14 units of alcohol weekly (1 unit = 360 mL of beer or 45 mL of spirit with 40% alcohol or 150 mL of wine), or those who could not guarantee the abandonment of drinking during the study, or subjects with positive result of alcohol breath test. 10. Subjects who smoke more than 5 cigarettes daily within 3 months prior to screening or those could not guarantee the abandonment of smoking during the study. 11. Those who have participated in any other drug clinical trial within 3 months prior to screening (with the last visit date of the trial considered as the starting time for time counting). 12. Those who donated blood or blood products of ≥400ml or 2 units within 3 months or had lost of ≥400 mL blood within 6 months prior to screening. 13. Those who do not agree to stop alcohol drinking or caffeinated beverages within 48 hours before the study drug administration and throughout the whole trial, or do not agree to stop strenuous exercise or to avoid other factors that may affect the drug absorption, distribution, metabolism, or excretion. 14. Women who are pregnant or lactating, or who have a positive pregnancy test before the study drug administration; or those who could not or do not take the requested effective contraceptive measures accepted by the investigator during the trial. 15. Subjects with difficulties in venous blood collection, fear of needles or hemophobia. 16. Other conditions that may not be suitable for participating in the study judged by the investigator.