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Examples of some valid identifier names are Employee123, mygood_book, _address93, FirstName,
age, etc.
Examples of some invalid identifier names are 1_Name, @Address, 1234, –Age, etc.
Keywords
Keywords are the reserved words that cannot be used as identifier names as they carry a special
meaning for the Java compiler. Some of the Java keywords are given below:
Java Keywords
abstract const float interface static
boolean continue for long switch
break default goto new this
byte do if private throw
case double implements protected throws
catch else import public try
char extends instanceof return void
class final int short while
The keywords const and goto cannot be used in Java. They were added to the list of keywords so
that they would generate compiler errors for developers who were converting C and C++ code
over to Java.
There are three more reserved words in Java: true, false, and null. Technically, they are literal
values and not keywords. However, they cannot be used as identifiers, and they have a specific
meaning to the Java compiler.
Data Types
A data type is used to define the size and type of value that a variable can store. The Java
language is rich in its data types. Java provides two types of data types: primitive and
non-primitive.
Primitive Data Types
Java provides eight basic data types, which are as given in the following table:
Data Type Size (in bits) Minimum Value Maximum Value
byte 8 –128 127
short 16 –32768 32767
int 32 –2147483648 2147483647
long 64 –9223372036854775808 9223372036854775807
char 16 0 65535
float 32 1.4E –45 3.4028235E38
double 64 4.9E –324 1.7976931348623157E308
boolean 1 True or false
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