Java Keywords
Last Updated :
09 Dec, 2024
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In Java, Keywords are the Reserved words in a programming 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.
Example :
// Java Program to demonstrate Keywords
class GFG
{
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("Succesful Demonstration"
+" of keywords");
}
}
}
Output
Succesful Demonstration of keywords
Java Keywords List
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.
| Keyword | Usage |
|---|---|
| abstract | Specifies that a class or method will be implemented later, in a 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 | A data type that can hold True and False values only |
| break | A control statement for breaking out of loops. |
| byte | 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 |
| char | A data type that can hold unsigned 16-bit Unicode characters |
| class | Declares a new class |
| continue | Sends control back outside a loop |
| default | Specifies the default block of code in a switch statement |
| do | Starts a do-while loop |
| double | A data type that can hold 64-bit floating-point numbers |
| else | Indicates alternative branches in an if statement |
| enum | A Java keyword is used to declare an enumerated type. Enumerations extend the base class. |
| extends | Indicates that a class is derived from another class or interface |
| final | Indicates that a variable holds a constant value or that a method will not be overridden |
| finally | Indicates a block of code in a try-catch structure that will always be executed |
| float | A data type that holds a 32-bit floating-point number |
| for | Used to start a for loop |
| if | Tests a true/false expression and branches accordingly |
| implements | Specifies that a class implements an interface |
| import | References other classes |
| instanceof | Indicates whether an object is an instance of a specific class or implements an interface |
| int | A data type that can hold a 32-bit signed integer |
| interface | Declares an interface |
| long | A data type that holds a 64-bit integer |
| native | Specifies that a method is implemented with native (platform-specific) code |
| new | Creates new objects |
| null | This indicates that a reference does not refer to anything |
| package | Declares a Java package |
| private | An access specifier indicating that a method or variable may be accessed only in the class it’s declared in |
| 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) |
| 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) |
| return | Sends control and possibly a return value back from a called method |
| 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) |
| strictfp | A Java keyword is used to restrict the precision and rounding of floating-point calculations to ensure portability. |
| super | Refers to a class’s base class (used in a method or class constructor) |
| switch | A statement that executes code based on a test value |
| synchronized | Specifies critical sections or methods in multithreaded code |
| this | Refers to the current object in a method or constructor |
| throw | Creates an exception |
| throws | Indicates what exceptions may be thrown by a method |
| transient | Specifies that a variable is not part of an object’s persistent state |
| try | Starts a block of code that will be tested for exceptions |
| void | Specifies that a method does not have a return value |
| volatile | This indicates that a variable may change asynchronously |
| while | Starts a while loop |
sealed | The sealed keyword is used to declare a class as “sealed,” meaning it restricts which classes can extend it. |
permits | The permits keyword is used within a sealed class declaration to specify the subclasses that are permitted to extend it. |
Example: Using the keywords as variables name. It will give an error as shown.
// Java Program to illustrate what if
// we use the keywords as the variable name
class GFG
{
public static void main(String[] args)
{
// Note "this" is a reserved
// word in java
String this = "Hello World!";
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
Important Points:
- The keywords const and goto are reserved, even though they are not currently in use.
- Currently, they are no longer supported 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.
FAQs – Java Keyowrds
What are the keywords of Java?
Keywords are the reserved words in Java having certain meanings. These words are not allowed to use as variable names or object names.
How many keywords are in Java?
There are 67 Keywords in Java.
