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Keywords in Java
Every programming language has special reserved words, or keywords, that have specific meanings and restrictions around how they should be used. Java is no different. Java keywords are the fundamental building blocks of any Java program. Keywords are an essential part of a language definition. They implement specific features of the language. These keywords, combined with operators and separators according to syntax, form definition of the Java language.
In this chapter, you’ll find a basic introduction to all Java keywords along with other resources that will be helpful for learning more about each keyword.
Java language has reserved 50 words as keywords that cannot be used as variable names, function names, or any other identifiers. Since keywords have specific meaning in Java, we cannot use them as names for variables, classes, methods and so on. All keywords are to be written in lower-case letters. Since Java is case-sensitive, one can use these words as identifiers by changing one or more letters to upper case. However, it is a bad practice and should be avoided.
The keywords const and goto are reserved but not used. In addition to the keywords, Java reserves true, false, and null. These are values defined by Java. You may not use these words for the names of variables, classes, and so on. Below tables lists all the keywords. It is not needed to memorize all the below keywords. You will learn about different keywords in different chapters.
Keywords for Class - Building - Handling - Managing Tools
abstract | to define an abstract class and abstract method |
extends | Extending classes and interfaces (by another interface only ) |
implements | implementing interfaces |
import | import and static import |
package | package declaration |
Keywords for Exception Handling
try | Exception handling |
throw | throwing Exception |
catch | Exception handling |
assert | added by java 1.4 to Create a Mechanism for doing Pre and Post Validation methods pre validation on public methods should not be done using assert |
finally | used with Exception |
Keywords for Object Reference
super | calling super class constructor , super class methods , super class members |
this | refence to current Object , accessable only to non-static methods and initialisers , also has a special meaning in constructors, though non inconsistent . |
Reserved keywords for future
strictfp | Reserved for future |
const | Reserved for future |
goto | Reserved for future |
Modifier keywords
final | modifier to represent contants |
private | Access modifier |
protected | Access modifier |
public | access definition |
synchronized | used with Multithreading |
volatile | used to suggest to compilier not to Optimise this variable since this can be modified unexpectedly. |
transient | specifies that the data should not be serialized |
native | defining native methods |
static | creating Static members for a Class |
Flow control keywords
while | used in loops , while and do-while |
do | used with do-while loop |
for | for loop |
break | used with switch case and for loops |
continue | used with loops to continue with next interation |
switch | switch case condition |
case | switch case statement |
default | used with switch case |
if | if condition |
else | else clause of if CONDITION |
return | return a value to called method |
Keyword operators in the sense that, they could well be functions
instanceof | checks if Object is an instance of class |
new | creating objects on the heap |
Data and Data Types keywords
boolean | datatype |
byte | datatype |
char | datatype |
short | datatype |
int | datatype |
long | datatpe |
class | to define a class |
enum | defining enumeration |
interface | interface definition |
float | datatype |
double | datatype |
void | key word which says that a ordinary method does not return anything |
null | represents a null reference |
TRUE | boolean literal |
FALSE | boolean literal |
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