Keywords in Java

Last Updated: 05 July, 2023

In this tutorial, we will discuss Java keywords. Java has a rich set of keywords, and each keyword has its own individual function and performs a specific task assigned to it.

In Java, Keywords are also known as Reserved Words. As these words are reserved and perform predefined tasks, Java does not allow the use of these reserved words (keywords) as identifier names (variables, methods, classes, interfaces, etc.).

We will get a compile-time error if we use these reserved words (keywords) as identifier names, as given in the below example.

Example: Don't use keywords as an identifier

  
  package com.javabytechie.keyword;
  public class Example {
    public static void main(String[] args) {
        String while = "some text value";	// Compile time error...
        int catch = 100;                    // Compile time error...
     }
  }

Exception in thread "main" java.lang.Error: Unresolved compilation problems: String cannot be resolved to a variable Syntax error on token "while", delete this token Syntax error on token "catch", invalid VariableDeclaratorId at com.javabytechie.keyword.Example.main(Example.java:4)

Let's have a look at the list of Java keywords or reserved words given in the below table:

S.No.	Keyword	Purpose of Use
1.	abstract	Used for classes and methods: If we declare a class with the abstract keyword, then that class is known as an abstract class, and we cannot create objects of that class. If we declare a method with the abstract keyword, then that method is known as an abstract method. An abstract method does not have a body; its body will be written in the 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	It is a data type that can hold either a True or False value.
4.	break	It is used to break a loop or switch statement. It breaks the current flow of the program at specified conditions.
5.	byte	It is 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. It must be used after the try block.
8.	char	A data type that can hold unsigned 16-bit Unicode characters.
9.	class	Used to declare a Java class.
10.	continue	Sends control back outside a loop. It continues the current flow of the program and skips the remaining line of code at the specified condition.
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 or 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	It is an access modifier used to restrict methods and variables of a class access outside.
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 is used for classes, interfaces, methods, and variables to indicate 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.

S.No.

Keyword

Purpose of Use

abstract

Used for classes and methods: If we declare a class with the abstract keyword, then that class is known as an abstract class, and we cannot create objects of that class.

If we declare a method with the abstract keyword, then that method is known as an abstract method. An abstract method does not have a body; its body will be written in the subclass.

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.

boolean

It is a data type that can hold either a True or False value.

break

It is used to break a loop or switch statement. It breaks the current flow of the program at specified conditions.

byte

It is a data type that can hold 8-bit data values.

case

Used in switch statements to mark blocks of text.

catch

Catches exceptions generated by try statements. It must be used after the try block.

char

A data type that can hold unsigned 16-bit Unicode characters.

class

Used to declare a Java class.

10.

continue

Sends control back outside a loop. It continues the current flow of the program and skips the remaining line of code at the specified condition.

11.

default

Specifies the default block of code in a switch statement.

12.

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.

Tests a true or 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

It is an access modifier used to restrict methods and variables of a class access outside.

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 is used for classes, interfaces, methods, and variables to indicate 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.

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.