# Java Programs
➤ Introduction to Java
➤ Java Editions & Concepts
➤ JDK JRE JVM JIT in Java
➤ How to Run Java program
➤ Java Hello World program
➤ How to set the Java path
➤ Classpath Environment
➤ Tokens in Java Language
➤ List of Java Keywords
➤ Identifiers in Java
➤ Data types in Java
➤ Float & double in Java
➤ Literals in Java
➤ Escape Sequence In Java
➤ Unicode character set
➤ String data type in Java
➤ Arithmetic operators in Java
➤ Increment and Decrement
➤ Comments in Java
➤ Java Naming Conventions
➤ Static Import in Java
A predefined identifier that has special meaning in a Java program outside comment and string is called a Keyword. Or, A keyword is a reserved word in Java language inside the compiler and JVM that perform a unique and special operation. A word that is created as part of the compiler and JVM software to represent a value is called Reserved words. We will see the complete list of Java keywords in detail.
In Java, there are 64 reserved words, among them 51 are keywords, 3 are literals and 10 restricted words are there.
Reserved words (64)
- Keywords (51)
- Literals (3)
- Restricted words (10)
Keywords are used to communicate with compiler and JVM to perform one special operation on our program.
Java keywords list
We can categories Java keywords list based on their uses.
1) Java Keywords list used for data types or return types (9)
byte short int long
Floating point values
char boolean void
Among these 9 Java keywords list, the first 8 are used for both data type and return values. But “void” is used only for the return type. If the method doesn’t return any value then the return type of the method is void.
2) List of Java keywords used in control statements (11)
Used in conditional statements
if else switch case default
Keywords used in loop
do while for
Keywords used in control transfer
break continue return
3) Keywords used for modifiers (11)
static final abstract native transient volatile synchronized strictfp
private protected public
The “default” is not a keyword. When we don’t use any accessibility modifiier while declaring class/methods then by default its accessibility within the package.
4) Keywords used while defining a Java class (7)
Class related keywords
class interface enum
Inheritance relationship related keywords
Package related keywords
5) Object related keywords list (4)
this super instanceof new
6) Java keywords list used in Exception Handling (6)
try catch finally throw throws assert
7) Unused keywords (2)
8) Other keyword (1)
There are some important points related to Java keywords,
- In Java, every keyword is a reserved word but every reserved word is not a keyword.
- We can’t use a keyword for a user-defined identifier name. It can’t be used for variables, methods, class names.
- Except for underscore (
_), all remaining keywords are the combination of lowercase letters and doesn’t contain any digit and special characters.
Among these keywords, most of them are given in the Java1.0 version onwards but some of them were introduced later. Those keywords list with java version is given below.
Unused Keywords in Java
Among 51 keywords, 49 keywords are used keywords and 2 are unused keywords. The unused kwywords are:- goto and const.
In Java, goto doesn’t have any special meaning, so it might be used as an identifier. If we use the goto keyword as an identifier, then the programmers coming from C, C++, and Python will get confusion. It had already created a lot of problems in many languages. Therefore, it is not allowed to use the goto keyword in Java.
In C/C++ the const keyword is used to define the variables as constant. In Java final keyword is already there to define constant, which is applicable on variables/methods. So, the const keyword is also not allowed in Java.
From the Java9 version onwards we can’t use a single underscore(
_) as an identifier either for naming a class/variable/method or any other programming element. But identifiers like hello_world are valid because it is using underscore. Underscore(
_) is added as a keyword for not getting conflicts with other languages like Python. We can use Java9 JVM either for running Python or Java-based programs. To run Python programs in JVM software a new rule is created that is:- underscore(_) is not allowed as an identifier as per Python rule. So, the same rule is implemented in Java compiler software.
Java doesn’t require “goto”, “const” and ‘_’ keywords hence they aren’t implemented. Even though they aren’t required, Java designers created them as keywords for stopping Java programmers to use them as user-defined identifiers in their programs. If we use them in our Java program then we will get a compile-time error.
Table with all Java keywords
Reserved literals in Java
These three are reserved words and literals(value), not keywords. Even though these words are not keywords we can’t use them as user-defined identifiers. Boolean literals are used for boolean data types. The null is the default value for an object reference.
Restricted Words in Java
To support the Java9 module system and to create and use the module in Java we got 10 restricted keywords. Restricted keywords mean these keywords are meant for use only in module programming. These keywords don’t have any meaning in regular programming inside a class/interface program. So, inside class/interface we can use them as a user-defined identifier. This facility added to support backward compatibility. It means for not getting errors on the project those are developed using Java8 or earlier version.
All the above 10 keywords can’t be used individually. Some keywords must use in combination with other keywords. We must use the
transitive keyword in combination with
requires keyword. We must use the keyword
to in combination with either
export or with
with must be used with
See:- Quiz on Java keywords
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