關鍵字 (keyword) 為具有語法功能的保留字 (reserved word) ，Java 的關鍵字共有 50 個，如以下列表
| abstract | continue | for | new | switch |
| assert*** | default | goto* | package | synchronized |
| boolean | do | if | private | this |
| break | double | implements | protected | throw |
| byte | else | import | public | throws |
| case | enum**** | instanceof | return | transient |
| catch | extends | int | short | try |
| char | final | interface | static | void |
| class | finally | long | strictfp** | volatile |
| const* | float | native | super | while |