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Java Constants, Variables & Data Types Explained

This chapter delves into the concepts of Java constants, variables, and data types, explaining their definitions, declarations, and scopes. Learn about fixed values, storage locations, primitive and non-primitive data types, and declaration rules with examples.

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Java Constants, Variables & Data Types Explained

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  1. Chapter 2 Constants, Variables & Data types • Constants Variables • Data types • Declaration of Variables • Giving Values to Variables • Scope of variable ie cmd X

  2. Constants Constants in Java refers to fixed values that do not change during execution of a prog. Java Constants Numeric constantsCharacter constants ie cmd Integer const. Real const. Char const. String const. X

  3. Variables A variable is an identifier that denotes a storage location used to store a data value Ex. Average, height, classStrength … etc • A variable names may consists of alphabets, digits, the ( _ ) • and $ char. Subject to the following conditions. • They must not begin with digit. • Uppercase and lowercase are distinct. • It should not be a keyword. • White space is not allowed. • Variable name can be of any length. ie cmd X

  4. Data types Data types specify the size and type of values that can be stored. Java data types ie Primitive Non-primitive cmd Numeric Non-numeric Classes Arrays X Integers Floats Char Boolean Interface (2 bytes) Byte (1 byte) Short (2 bytes) int (4 bytes) Long (8 bytes) Float (4 bytes) Double(8 bytes) (1 bit)

  5. Declaration of variables Declaration does three things • It tells the compiler what the variable name is. • It specifies what type of data the variable will hold. • The place of declaration (in the program) decides the scope • of the variable. ie The variable must be declared before it is used in the program. The general form of declaration of variable is: type variable1, variable2……… variableN. int count; float x, y; byte b; char c1, c2; cmd X

  6. Declaration of variables A variable must be given a value after it has been declared but before It is used in an expression. This can be achieve in two ways: • By using an assignment operator. • By using a read statement. • int finalvalue = 100; ie cmd Read statement program using DataInputStream X

  7. Scope of variables The area of the program where the variable is accessible (usable) called its scope Java variables area actually classified into three kinds: • Instance variables: These are created when the objects are • instantiated and therefore they are associated with objects. • Class variables: Class variables are global to class and • belongs to the entire set of objects that class creates. • 3. Local variables: The variables declared inside the methods • are called local variables. ie cmd X

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