(toc)

Java keywords are reserved words that have predefined meanings in the Java programming language. These cannot be used as identifiers (variable names, method names, class names, etc.) because they serve specific purposes in the language’s syntax and structure.

List of Java Keywords

Here is a complete list of Java’s reserved keywords:

Category Keywords
Control Flow if, else, switch, case, default, do, while, for, break, continue, return, goto
Access Modifiers private, protected, public
Class Modifiers class, abstract, final, interface, enum
Object Handling new, this, super, instanceof
Exception Handling try, catch, finally, throw, throws
Data Types byte, short, int, long, float, double, char, boolean
Others static, void, volatile, synchronized, native, transient, strictfp, assert, import, package
Reserved for Future const, null, true, false (Though null, true, and false are literals, they are reserved words).

Categories of Keywords

1. Control Flow Keywords

These are used to control the flow of execution in a program.

  • if, else: Used for conditional branching.


    if (x > 0) {
    System.out.println("Positive");
} else {
    System.out.println("Negative");
}

  • switch, case, default: Used for multi-way branching.


    switch (day) {
    case 1: System.out.println("Monday"); break;
    default: System.out.println("Invalid day");
}

  • break, continue: Used to exit or skip loops.

  • return: Exits a method and optionally returns a value.

2. Access Modifiers

Define the visibility of classes, methods, and variables.

  • public: Accessible from anywhere.
  • protected: Accessible within the same package or subclasses.
  • private: Accessible only within the same class.

3. Class and Object Handling

  • class, abstract, interface: Used to define classes or interfaces.
  • this: Refers to the current object.
  • super: Refers to the parent class.

4. Exception Handling

These keywords handle runtime errors in programs.

  • try, catch, finally: Used to handle exceptions. 

    try {
    int result = 10 / 0;
} catch (ArithmeticException e) {
    System.out.println("Cannot divide by zero.");
} finally {
    System.out.println("End of program.");
}

5. Primitive Data Types

Define variables with specific data types.

  • int, float, double: Numeric types.
  • char: Character type.
  • boolean: True or false values.

Special Keywords

1. static

Defines a class-level member shared across all objects.


class Example {
    static int count = 0;
}

2. final

Defines constants or prevents inheritance/overriding.


final int MAX = 100; // Value cannot change

3. volatile

Indicates that a variable’s value can be changed by multiple threads.

Reserved Keywords

Java reserves certain keywords for future use:

  • goto: Reserved but not implemented.
  • const: Use final instead.

Key Points

  1. Keywords cannot be used as identifiers.
  2. Java is case-sensitive: int is a keyword, but Int is not.
  3. Reserved keywords like goto and const are not currently in use but cannot be used as identifiers.

Leave a Reply