Java Variables and Scopes

What is variable in java?

  • Variable: is the basic unit of storage in a java program.
  • A variable is defined by the combination of an identifier, a type, and initialized value(optional).
  • All variables have a scope in the program, scope defines the variables visibility, and a lifetime in the java code.
  • Declaring a variable in java:
    • All variables must be declared before using in the java code.
    • Syntax: type identifier [=value][, identifier [= value]...];
    • type is Java simple data types or name of a class or interface.
    • identifier is the name of the variable.
    • we can initialize the variable by specifying an equal sign and a value.
    • More than one variable can be declared using the comma-separated list.
      Here are some examples of variable declarations of different data types.
      // declares two integer variables a and b.
      int a, b;
      // declares three integer variables num1, num2, and num3, also num1 and num3 are initialized with 15 and 25.
      int num1 = 15, num2, num3 = 25;
      // declares double variable pi with initialized value 3.14.
      double pi = 3.14;
      // declares character variable with initialized char value 'J'.
      char ch = 'J';

What is dynamic initialization in java?

  • Java allows any variables to be initialized dynamically using expression.
  • Privious examples are based on constants to initialize variables(which is static initialization).
  • Dynamic initialization example:
    // Dynamic initialization in java                                               
    class DynamicInitializationTest {                                               
     public static void main(String args[]) {                                       
      double a = 6.0, b = 5.0;                                                      
      // double variable c is here dynamically initialized                          
      // based on below expression                                                  
      double c = ((a * a) + (b * b));                                               
      System.out.println("c = ((a*a) +(b*b)): " + c);                               
    c = ((a*a) +(b*b)): 61.0

What is Scope and Lifetime of variables?

  • Most programming languages define two general categories of scopes: glopal and local.
  • Two major scopes in java are those defined by the class and those defined by the method.
  • Scope defined by a method begins with its opening curly brace.
  • Variables declared inside the a scope are not visible(accessible) to code that is defined outside the scope. When declaring a variable within a scope, localizing that variable and protecting it from unauthorized access or modification. this scope rules provide the foundation for encapsulation in java.
    // Scope and lifetime of variables in java                                      
    class ScopeTest {                                                               
     public static void main(String args[]) {                                       
      //Visible or accessible this double variables within main method              
      double a = 6.0, b = 5.0;                                                      
      double d = 0.0d;                                                              
      if (a > 5.0) {                                                                
       // double variable c is visible to only if block                             
       double c = 7.0;                                                              
       // variables a and b are visible in if block since inner block for method main.
       System.out.println("a and b: " + a + " " + b);                               
       d = a + b + c;                                                               
      // c is not visible here, gets the java compiler error                        
      //c = 4.0;                                                                    
      System.out.println("d = (a + b + c): " + d);                                  
    a and b: 6.0 5.0
    d = (a + b + c): 18.0
Java Programming Language Examples

GCD and Rational Number Java Program

Java Queue Program using exception

Java Stack Program using exception

Addition of three integers java program

Biggest of three integers java program

Fibonacci numbers java program

Arithmetic Operations Menu java program

Second Smallest Element In Array Java Program

Transpose Of A Matrix Java Program

Java Program to Display triangle of stars (*)

Java Programming Prints Product Tables

Java Program to Display triangle of numbers

Java Programming Gets Current Date

Java Programming Finds Character Vowel or Consonent

Java Programming HCF and LCM Computation

Java Programming Sum of Command Line Integer Arguments

Java Programming Multiplication of Command Line Integer Arguments

Java Programming Multiplication of Command Line Floating Point Numeric Arguments

Java Programming String Contains or Not

Java Programming Gets Grade Description using Switch

Java Programming CSV File Reader

Java Programming Character Frequency Count in String using for each

Java Programming Finds Min from Integer Array by Passing Array to Method

Java Programming Linear Search

Java Programming Binary Search

Java Programming Ternary Search

Java Programming Generates Range of Numbers

Java Programming Generates Range of Characters

Java Programming Computes Square Root Value

Java Programming Checks Number is Positive or Negative

Java Programming Checks Number is Odd or Even

Java Programming Computes Plot Area

Java Programming Convert Number of Days into Years

Java Programming Checks a Year is Leap Year, Century Year or Not

Java Programming Checks a Character is Digit, Letter or neither digit nor letter

Java Programming Checks a Number is Palindrome or not

Java Programming Sum of Two Matrix

Java Programming Power Computation

Java Programming Checks Number is an Armstrong Number or not

Java Programming Temperature Unit Conversions

Java Programming Generates Random Numbers in Specified Range

Java Programming Computes Sum of Digits and Product of Digits

Java Programming Computes Reverse Number

Java Programming Computes Factorial Value

Java Programming Checks Prime Number or not

Java Programming Computes Harmonic Series

Java Programming Generates Floyd's Triangle

Java Programming Reverses String

Java Programming Checks Palindrome String or not

Java Programming Opens Notepad

Java Programming Searches String using RegEx Pattern

Java Programming Searches Word in String

Java Programming Gets System Environment Variables

Java Programming Gets IP Address of Server Name

Java Programming Arrays Sort and Reverse using sort method

Java Programming Bubble Sorting

Java Programming Selection Sorting

Java Programming Insertion Sorting

Java Programming Merge Sorting

Java Programming Quick Sorting

Java Programming Counting Sort

Java Programming Radix Sorting

Java Programming Sorting Array of Strings

Java Programming String Characters Sorting

Java Programming Sum of First N Numbers

Java Programming Product of First N Numbers

Java Program to get URL details

Java Program to get URL HTML Content

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