Keywords On this page Java has 50+ reserved keywords (as of Java 17). These are reserved by the language and cannot be used as identifiers (variable names, class names, etc.).
We’ll break them into logical groups and explain purpose, usage, and nuances of each with code examples.
📦 1. Data Types & Literals # These define the type of data.
Keyword Meaning int32-bit integer long64-bit integer short16-bit integer byte8-bit integer float32-bit floating point double64-bit floating point char16-bit Unicode character booleantrue or false true, false, nullliterals
🔸 null is not a keyword but a reserved literal in Java.
🧱 2. Access Modifiers # These control visibility.
Keyword Purpose publicVisible everywhere privateVisible only in the same class protectedVisible in the same package + subclasses default(No keyword) Package-private
Keyword Purpose classDefines a class interfaceDeclares an interface enumDeclares an enumeration extendsInherits from a class implementsImplements an interface newCreates an object thisRefers to current object superRefers to parent class
🔁 4. Control Flow # Keyword Purpose if / elseBranching switch, case, defaultMulti-way branching while, do, forLoops break, continueControl loop execution returnExit method yieldReturn value from a switch expression (Java 14+)
⚙️ 5. Exception Handling # Keyword Purpose tryStart of exception block catchHandle the exception finallyAlways executes throwUsed to throw exception throwsDeclares possible exceptions
🔐 6. Object Behavior Modifiers # Keyword Purpose staticBelongs to the class, not instance finalCannot be changed/overridden abstractDeclares incomplete method/class synchronizedUsed in multithreading to control access volatilePrevents thread caching for variables transientSkips variable during serialization nativeCalls code written in another language (C/C++) strictfpEnsures consistent floating-point calculations across platforms
🧬 7. Inheritance and Polymorphism # Keyword Purpose extendsSubclassing (class inheritance) implementsInterface implementation instanceofChecks runtime type superAccess parent class methods/constructors
👨👩👧 8. Concurrency (Threads) # Keyword Purpose synchronizedEnsures atomic access to code block volatileGuarantees visibility of changes across threads
📦 9. Package and Import # Keyword Purpose packageDeclares package name importImports other packages/classes
📐 10. Miscellaneous # Keyword Purpose assertDebugging tool for assumptions instanceofCheck if object is of a specific type gotoReserved but not used in Java constReserved but not used (use final instead)
🆕 Bonus: New Keywords in Recent Java Versions # Keyword Purpose varLocal variable type inference (Java 10+) recordImmutable data class (Java 14+) sealed, permits, non-sealedRestricted class hierarchy (Java 15+)