The Java reserved words are listed below. Some of the keywords have no current meaning and are reserved for future expansion.

Literals are the representation of values.

• Integers (hexadecimal, decimal, octal)
• Floating Point numbers
• Booleans (true or false)
• Characters
• Strings
• String Literals :

\n new line \ r carriage return

\ t tab \ " double quote

\ ‘ single quote \ \ backslash

There are two regular comment styles, and a special comment style used to generate class library documentation.

// This is a comment

/ * This is a comment * /

/ * * This is a special comment for documentation * * /

Variables (identifiers) are names for classes, methods, variables and blocks. As in all programming languages, Java variables adhere to some rules, namely:

• the first character must be a letter, $ or _ (underscore)
• any character after the first one may be numeric
• identifiers are case-sensitive
• must be meaningful *

There are 3 kinds of variables in Java:

• used to define the attributes of a particular object.
• declared outside the method definition
• used when storing information needed by multiple methods in the object.

sum = num1 + num2;

}

public void paint (Graphics g ) {

g . drawString ("The sum is "+sum, 35, 100 ) ;

}

}

In the example, variables num1 and num2 of type integer and sum of type double are declared as instance variables. These variables, therefore, can be accessed anywhere in the program (inside or outside a method). [Instance Variables, 5 of 8]

• similar to instance variables, except that their values apply to all class’instances (and to the class itself) rather than having different values for each object.
• uses the static keyword

class VariableDemo {

Static int [] = {1, 2, 3, 4, 5, 6, 7 } ;

}

The array i which is an array of integers is declared as a class variable with a static value of{1,2,3,4,5,6,7}. Array i, being a class variable, is therefore accessible to the class and all its instances. [Class Variable, 6 of 8]

• declared and used inside method definitions.
• once a method (or block) finishes executing, the variable definition and its values cease to exist.

class VariableDemo {

String str ;

public void displayString {

boolean more ;

if (more) . . .

}

The variable more which of type boolean is local to method displayString. Once displayString finishes its execution, the variable more does not exist and may not be used anywhere in the program. [Local Variables, 7 of 8]

Constants refers to those whose value does not change. In Java, the keyword final is used to refer to a constant.

class VariableDemo {

double charge1, charge2 ;

public void computeTemp () {

final double rate = 3.5 ;

}

}

The constant rate, which is of type double, has a constant value of 3.5. This value is retained throughout the course of the program. [Constants, 8 of 8]