Java Tokens
Java
keywords are also known as reserved words. Keywords are particular words that
act as a key to a code. These are predefined words by Java so they cannot be
used as a variable or object name or class name.
List of
Java Keywords:
1. abstract: Java abstract keyword is
used to declare an abstract class. An abstract class can provide the
implementation of the interface. It can have abstract and non-abstract methods.
2. boolean: Java boolean keyword is
used to declare a variable as a boolean type. It can hold True and False values
only.
3. break: Java break keyword is used to
break the loop or switch statement. It breaks the current flow of the program
at specified conditions.
4. byte: Java byte keyword is used to
declare a variable that can hold 8-bit data values.
5. case: Java case keyword is used with
the switch statements to mark blocks of text.
6. catch: Java catch keyword is used to
catch the exceptions generated by try statements. It must be used after the try
block only.
7. char: Java char keyword is used to
declare a variable that can hold unsigned 16-bit Unicode characters
8. class: Java class keyword is used to
declare a class.
9. continue: Java continue keyword is
used to continue the loop. It continues the current flow of the program and
skips the remaining code at the specified condition.
10.default: Java default keyword is used to specify the default
block of code in a switch statement.
11.do: Java do keyword is used in the control statement to declare
a loop. It can iterate a part of the program several times.
12.double: Java double keyword is used to declare a variable that
can hold 64-bit floating-point number.
13.else: Java else keyword is used to indicate the alternative
branches in an if statement.
14.enum: Java enum keyword is used to define a fixed set of
constants. Enum constructors are always private or default.
15.extends: Java extends keyword is used to indicate that a class
is derived from another class or interface.
16.final: Java final keyword is used to indicate that a variable
holds a constant value. It is used with a variable. It is used to restrict the
user from updating the value of the variable.
17.finally: Java finally keyword indicates a block of code in a
try-catch structure. This block is always executed whether an exception is
handled or not.
18.float: Java float keyword is used to declare a variable that can
hold a 32-bit floating-point number.
19.for: Java for keyword is used to start a for loop. It is used to
execute a set of instructions/functions repeatedly when some condition becomes
true. If the number of iteration is fixed, it is recommended to use for loop.
20.if: Java if keyword tests the condition. It executes the if
block if the condition is true.
21.implements: Java implements keyword is used to implement an
interface.
22.import: Java import keyword makes classes and interfaces
available and accessible to the current source code.
23.instanceof: Java instanceof keyword is used to test whether the
object is an instance of the specified class or implements an interface.
24.int: Java int keyword is used to declare a variable that can
hold a 32-bit signed integer.
25.interface: Java interface keyword is used to declare an
interface. It can have only abstract methods.
26.long: Java long keyword is used to declare a variable that can
hold a 64-bit integer.
27.native: Java native keyword is used to specify that a method is
implemented in native code using JNI (Java Native Interface).
28.new: Java new keyword is used to create new objects.
29.null: Java null keyword is used to indicate that a reference
does not refer to anything. It removes the garbage value.
30.package: Java package keyword is used to declare a Java package
that includes the classes.
31.private: Java private keyword is an access modifier. It is used
to indicate that a method or variable may be accessed only in the class in
which it is declared.
32.protected: Java protected keyword is an access modifier. It can
be accessible within the package and outside the package but through
inheritance only. It can't be applied with the class.
33.public: Java public keyword is an access modifier. It is used to
indicate that an item is accessible anywhere. It has the widest scope among all
other modifiers.
34.return: Java return keyword is used to return from a method when
its execution is complete.
35.short: Java short keyword is used to declare a variable that can
hold a 16-bit integer.
36.static: Java static keyword is used to indicate that a variable
or method is a class method. The static keyword in Java is mainly used for
memory management.
37.strictfp: Java strictfp is used to restrict the floating-point
calculations to ensure portability.
38.super: Java super keyword is a reference variable that is used
to refer to parent class objects. It can be used to invoke the immediate parent
class method.
39.switch: The Java switch keyword contains a switch statement that
executes code based on test value. The switch statement tests the equality of a
variable against multiple values.
40.synchronized: Java synchronized keyword is used to specify the
critical sections or methods in multithreaded code.
41.this: Java this keyword can be used to refer the current object
in a method or constructor.
42.throw: The Java throw keyword is used to explicitly throw an
exception. The throw keyword is mainly used to throw custom exceptions. It is
followed by an instance.
43.throws: The Java throws keyword is used to declare an exception.
Checked exceptions can be propagated with throws.
44.transient: Java transient keyword is used in serialization. If
you define any data member as transient, it will not be serialized.
45.try: Java try keyword is used to start a block of code that will
be tested for exceptions. The try block must be followed by either catch or
finally block.
46.void: Java void keyword is used to specify that a method does
not have a return value.
47.volatile: Java volatile keyword is used to indicate that a
variable may change asynchronously.
48.while: Java while keyword is used to start a while loop. This
loop iterates a part of the program several times. If the number of iteration
is not fixed, it is recommended to use the while loop.
Literal
In Java, a
literal is a fixed value that is directly written into the code and represents
the value of a variable. Literals are used to assign values to variables or
constants, and they are of various data types, such as numbers, characters,
strings, and booleans.
Types of Literals in Java:
1. Integer Literals:
Represent whole numbers.
Examples:
- Decimal: 10, 123
- Binary (prefix 0b or 0B): 0b1010
(equals 10)
- Octal (prefix 0): 012 (equals
10)
- Hexadecimal (prefix 0x or 0X):
0xA (equals 10)
2. Floating-Point Literals:
Represent decimal or real numbers.
Examples:
- 3.14, 2.0, 1.5e3 (equals 1.5 ×
10³ = 1500)
- By default, floating-point
literals are of type double. Use f or F for float, e.g., 3.14f.
3. Character Literals:
Represent a single character enclosed in single quotes (').
Examples:
- 'A', 'z', '1', '\n' (newline),
'\u0061' (Unicode character for 'a')
4. String Literals:
Represent a sequence of characters enclosed in double quotes (").
Examples:
- "Hello, World!",
"Java", "123"
5. Boolean Literals:
Represent true or false values.
Examples:
- true, false
6. Null Literal:
Represents the null reference. It is used to indicate that an object reference
does not point to any memory location.
Example:
- null
7. Underscore in Literals:
Since Java 7, underscores (_) can be used in numeric literals for
better readability.
Examples:
- 1_000_000 (equals 1000000)
- 0b1010_1010 (binary literal
with underscores)
Example in
Code:
public class LiteralsExample {
public static void main(String[] args) {
int decimal = 10; // Integer literal
int binary = 0b1010; // Binary literal
int octal = 012; // Octal literal
int hex = 0xA; // Hexadecimal literal
float pi = 3.14f; // Floating-point literal
double largeNum = 1.5e3; // Double
literal
char letter = 'A'; // Character literal
String message = "Hello,
Java!"; // String literal
boolean isJavaFun = true; // Boolean literal
Object obj = null; // Null literal
System.out.println("Decimal:
"
+ decimal);
System.out.println("Binary:
"
+ binary);
System.out.println("Octal:
"
+ octal);
System.out.println("Hexadecimal:
"
+ hex);
System.out.println("Pi:
"
+ pi);
System.out.println("Large
Number: " + largeNum);
System.out.println("Letter:
"
+ letter);
System.out.println("Message:
"
+ message);
System.out.println("Is Java
Fun? " + isJavaFun);
System.out.println("Object:
"
+ obj);
}
}
Identifier,
In Java (and most
programming languages), an identifier is the name used to identify
variables, methods, classes, or other user-defined elements in a program. It is
a sequence of characters that adheres to specific naming rules.
Key Characteristics of
Identifiers:
1. User-Defined Names:
Identifiers are names given by the programmer to elements like variables,
methods, classes, etc.
2. Rules for Identifiers:
- Allowed Characters: Identifiers can include
letters (A-Z, a-z), digits (0-9), underscore (_), and dollar sign ($).
- Cannot Start with a Digit: Identifiers must begin with
a letter, an underscore, or a dollar sign but not a digit.
- ✅
myVar
- ❌
1variable
- No Reserved Words: Identifiers cannot be the
same as Java's reserved keywords (e.g., class, int, public).
- ✅
myClass
- ❌
class
- Case-Sensitive: Identifiers are
case-sensitive. For example, MyVariable and myvariable are different
identifiers.
- Unlimited Length: Java identifiers can be of
any length.
3. Convention (Not Mandatory):
While not enforced, these naming conventions improve code readability:
- Use camelCase for
variables and methods (myVariable, calculateSum).
- Use PascalCase for
class names (MyClass, UserProfile).
- Use UPPER_CASE_WITH_UNDERSCORES
for constants (MAX_VALUE, PI).
- Avoid using $ unless
auto-generated (e.g., by a tool).
Examples of Valid and
Invalid Identifiers:
Valid Identifiers:
myVariable_temp$priceemployeeCountMAX_VALUE
Invalid Identifiers:
1stValue(starts with a digit)#price(contains an invalid character#)int(reserved keyword)employee-name(contains a hyphen-)
Example in
Code:
public class IdentifierExample {
public static void main(String[] args) {
int age = 25; // 'age' is an identifier for
the variable
double _price = 99.99; // '_price' is a valid identifier
String $name = "John"; // '$name' is a valid identifier
final int MAX_LIMIT = 100; // 'MAX_LIMIT' is an identifier for a
constant
System.out.println("Age:
"
+ age);
System.out.println("Price:
"
+ _price);
System.out.println("Name:
"
+ $name);
System.out.println("Max
Limit: " + MAX_LIMIT);
}
}