Java Keywords

In Java, keywords are the reserved words that have some predefined meanings and are used by the Java compiler for some internal process or represent some predefined actions. These words cannot be used as identifiers such as variable names, method names, class names, or object names. 

Now, let us go through a simple example before a deep dive into the article.

class Geeks {
    
    public static void main(String[] args)
    {
      	// Using final and int keyword
        final int x = 10;
      
      	// Using if and else keywords
      	if(x > 10){
           System.out.println("Failed");
        }
      	else {
           System.out.println("Successful demonstration"
                              +" of keywords.");
        }
    }
}

Successful demonstration of keywords.

What Happens if we use a Variable Name same as keyword?

Using a keyword as a variable name would give error as shown below.

class Geeks 
{
    public static void main(String[] args)
    {
        String this = "Hello World!";
        System.out.println(this);
    }
}

Output:

./Geeks.java:5: error: not a statement

String this = "Hello World!";

^

./Geeks.java:5: error: ';' expected

String this = "Hello World!";

2 errors

Important Points:

• The keywords const and goto are reserved, even though they are not currently used in Java.
• true, false, and null look like keywords, but in actuality they are literals. However, they still can't be used as identifiers in a program.
• In Java, keywords are case-sensitive, and writing Java keywords in upper case (like IF instead of if) will throw an error.

Java Keywords List (As of Java 21)

Java keywords are reserved words that have predefined meanings in the language. They cannot be used as identifiers (like variable or method names).

As of Java 21, there are 53 keywords, categorized below by their usage and purpose.

1. Data Type Keywords

Used to define variable types and specify the kind of data they can hold.

2. Control Flow Keywords

Used to control the execution flow of a program, including loops, branching, and jumps.

3. Exception Handling Keywords

Used for handling and managing runtime errors in programs.

4. Object-Oriented Keywords

Used to define classes, interfaces, and objects, as well as inheritance and encapsulation properties.

5. Access Control Keywords

Define the visibility or accessibility of classes, methods, and variables.

6. Package and Import Keywords

Used to organize classes and access external code.

7. Multithreading and Synchronization Keywords

Used to handle concurrent execution of code and ensure thread safety.

8. Memory Management and Object Serialization Keywords

Handle object persistence, garbage collection, and native method calls.

9. Modifier and Utility Keywords

Define additional behaviors and precision control.

10. Reserved (Unused) Keywords

These keywords are reserved but not currently used by Java.

11. Special Literals

Suggested Quiz

Edit Quiz

5 Questions

Which of the following is NOT a Java keyword?

• A

  volatile

• B

  goto

• C

  const

• D

  true

Explanation:

true, false, and null look like keywords but are actually boolean and null literals, not Java keywords. They cannot be used as identifiers but are not part of Java's keyword list.

What will happen if you use a Java keyword as a variable name?

• A

  The program runs normally

• B

  The compiler automatically renames it

• C

  Compilation error occurs

• D

  It becomes a string value

Explanation:

Java keywords are reserved words and cannot be used as variable names or identifiers. The compiler throws an error like: error: not a statement or ';' expected.

Which keyword is used to manually throw an exception?

• A

  throws

• B

  catch

• C

  throw

• D

  finally

Explanation:

throw is used inside methods to manually create and throw an exception object, e.g.,

throw new RuntimeException("Error");

Which keyword ensures only one thread accesses a block at a time?

• A

  synchronized

• B

  volatile

• C

  transient

• D

  static

Explanation:

synchronized is used in multithreading to lock a method/block so only one thread can execute it at a time, preventing thread interference.

Which category does the keyword extends belong to?

• A

  Control Flow

• B

  Exception Handling

• C

  Object-Oriented

• D

  Access Control

Explanation:

Quiz Completed Successfully

Your Score :   2/5

Accuracy :  0%

Login to View Explanation

1/5 1/5 < Previous Next >