Java Basics: Variables and Declarations

Variables in Java

• A variable in Java has three properties: data type, variable name, and value.
• The data type determines the type of value a variable can hold.
• The variable name is a unique identifier for the variable.
• The value is the actual data stored in the variable.

Primitive Data Types in Java

• byte, short, int, long, float, double, boolean, char are the numeric and boolean primitive data types in Java.
• String is not a primitive data type in Java.

Arithmetic Operations in Java

• The / operator is used for division in Java.
• The $14 / 4$ expression in Java results in 3 (integer division).
• The $20 % 3$ expression in Java results in 2 (modulus operator).
• The $9.0 / 2$ expression in Java results in 4.5 (floating-point division).
• The * operator is used for multiplication in Java.

Methods in Java

• A method in Java is a block of code that can be called multiple times from different parts of a program.
• A method has a name, return type, parameters, and a body.
• The access type of a method is defined by the access modifier (public, private, etc.).
• A method with no return value has a return type of void.
• Parameters in a method are used to pass values to the method.
• To call a method m1 from class A in another class B, an object of class A needs to be created, and then the method can be called using the object.

Constants in Java

• An effectively constant variable in Java is declared using the final keyword.
• Java constants are typically declared using the final static keywords.
• Comments in Java are indicated using // for single-line comments and /* */ for multi-line comments.
• Java identifiers can contain letters, digits, _, and $, but cannot start with a digit.
• The role of an identifier in Java is to name a variable, method, or other programming element.
• The keyword package precedes package identifiers in Java.

Method Declaration in Java

• A method declaration in Java specifies the method's name, return type, parameters, and access type.
• The void keyword indicates that a method does not return a value.
• A static variable declared with the final modifier in Java is a constant and cannot be changed once initialized.
• Variables in Java can be initialized using the assignment operator (=).