List of all Java Keywords

Keywords or Reserved words are the words in a language that are used for some internal process or represent some predefined actions. These words are therefore not allowed to use as variable names or objects. If we do we will get a compile-time error as shown below as follows:

Illustration:

Java

// Java Program to Illustrate What If We use the keywords as the variable name
// Code Contributed by @Shubham Jain

class HelloWorld {
    public static void main(String[] args)
    {

        String this = "Hello World!"; // Note "this" is a reserved word in java
        System.out.println(this);
    }
 }

Output:

./HelloWorld.java:6: error: not a statement
        String this = "Hello World!";         System.out.println(this);
        ^
./HelloWorld.java:6: error: ';' expected
        String this = "Hello World!";         System.out.println(this);
              ^
2 errors

Java contains a list of keywords or reserved words which are also highlighted with different colors be it an IDE or editor in order to segregate the differences between flexible words and reserved words. They are listed below in the table with the primary action associated with them.

S.No	Keyword	Usage
1.	abstract	Specifies that a class or method will be implemented later, in a subclass
2.	assert	Assert describes a predicate placed in a java program to indicate that the developer thinks that the predicate is always true at that place.
3.	boolean	A data type that can hold True and False values only
4.	break	A control statement for breaking out of loops.
5.	byte	A data type that can hold 8-bit data values
6.	case	Used in switch statements to mark blocks of text
7.	catch	Catches exceptions generated by try statements
8.	char	A data type that can hold unsigned 16-bit Unicode characters
9.	class	Declares a new class
10.	continue	Sends control back outside a loop
11.	default	Specifies the default block of code in a switch statement
12.	do	Starts a do-while loop
13.	double	A data type that can hold 64-bit floating-point numbers
14.	else	Indicates alternative branches in an if statement
15.	enum	A Java keyword is used to declare an enumerated type. Enumerations extend the base class.
16.	extends	Indicates that a class is derived from another class or interface
17.	final	Indicates that a variable holds a constant value or that a method will not be overridden
18.	finally	Indicates a block of code in a try-catch structure that will always be executed
19.	float	A data type that holds a 32-bit floating-point number
20.	for	Used to start a for loop
21.	if	Tests a true/false expression and branches accordingly
22.	implements	Specifies that a class implements an interface
23.	import	References other classes
24.	instanceof	Indicates whether an object is an instance of a specific class or implements an interface
25.	int	A data type that can hold a 32-bit signed integer
26.	interface	Declares an interface
27.	long	A data type that holds a 64-bit integer
28.	native	Specifies that a method is implemented with native (platform-specific) code
29.	new	Creates new objects
30.	null	This indicates that a reference does not refer to anything
31.	package	Declares a Java package
32.	private	An access specifier indicating that a method or variable may be accessed only in the class it’s declared in
33.	protected	An access specifier indicating that a method or variable may only be accessed in the class it’s declared in (or a subclass of the class it’s declared in or other classes in the same package)
34.	public	An access specifier used for classes, interfaces, methods, and variables indicating that an item is accessible throughout the application (or where the class that defines it is accessible)
35.	return	Sends control and possibly a return value back from a called method
36.	short	A data type that can hold a 16-bit integer
37	static	Indicates that a variable or method is a class method (rather than being limited to one particular object)
38.	strictfp	A Java keyword is used to restrict the precision and rounding of floating-point calculations to ensure portability.
39.	super	Refers to a class’s base class (used in a method or class constructor)
40.	switch	A statement that executes code based on a test value
41.	synchronized	Specifies critical sections or methods in multithreaded code
42.	this	Refers to the current object in a method or constructor
43.	throw	Creates an exception
44.	throws	Indicates what exceptions may be thrown by a method
45.	transient	Specifies that a variable is not part of an object’s persistent state
46.	try	Starts a block of code that will be tested for exceptions
47.	void	Specifies that a method does not have a return value
48.	volatile	This indicates that a variable may change asynchronously
49.	while	Starts a while loop

Note:

• The keywords const and goto are reserved, even they are not currently in use.
• Currently they are no longer supported in Java.

const	Reserved for future use
goto	Reserved for future use

• true, false and null look like keywords, but in actual they are literals. However they still can’t be used as identifiers in a program.
• These keywords cannot be used as a variable. Check out this article for more on the rules of variable declarations.