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);                               
     }                                                                              
    }  
    
    Output:
    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);                                  
     }                                                                              
    }   
    
    Output:
    a and b: 6.0 5.0
    d = (a + b + c): 18.0
    
Java 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 Program to Get Current Date

Java Program to Find Character Vowel or Consonent

Java Program to Compute HCF and LCM

Java Program to Sum the Command Line Integer Arguments

Java Programm to Multiply the Command Line Integer Arguments

Java Program to Find Multiplication of Command Line Floating Point Numeric Arguments

Java Program to Check String Contains or Not

Java Program to Get Grade Description using Switch

Java Program for CSV File Reader

Java Program to Find Character Frequency Count in String using for each

Java Program to Find Min from Integer Array by Passing Array to Method

Java Program Linear Search

Binary Search Java Program

Ternary Search Java Program

Java Program to Generate Range of Numbers

Java Program to Generate Range of Characters

Java Program to Compute Square Root Value

Java Program to Check Number is Positive or Negative

Java Program to Check Number is Odd or Even

Java Program to Compute Plot Area

Java Program to Convert Number of Days into Years

Java Program to Check a Year is Leap Year, Century Year or Not

Java Program to Check a Character is Digit, Letter or neither digit nor letter

Java Program to Check a Number is Palindrome or not

Java Program to Sum Two Matrix

Java Program to Compute Power

Java Program to Check Number is an Armstrong Number or not

Java Program for Temperature Unit Conversions

Java Program to Generate Random Numbers in Specified Range

Java Program to Compute Sum of Digits and Product of Digits

Java Program to Compute Reverse Number

Java Programming Computes Factorial Value

Java Programming Checks Prime Number or not

Java Program to Compute Harmonic Series

Java Program Generate Floyd's Triangle

Java Program to Reverse String

Java Program to Check Palindrome String or not

Java Program to Open Notepad

Java Program to Search String using RegEx Pattern

Java Program to Search Word in String

Java Program to Get System Environment Variables

Java Program to Get IP Address of Server Name

Java Program for Arrays Sorting and Reverse using sort method

Java Program for Bubble Sorting

Java Program for Selection Sorting

Java Program for Insertion Sorting

Java Program for Merge Sorting

Java Program for Quick Sorting

Java Program for Counting Sort

Java Program for Radix Sorting

Java Program for Sorting Array of Strings

Java Program for String Characters Sorting

Java Program to Sum First N Numbers

Java Program to Product First N Numbers

Java Program to get URL details

Java Program to get URL HTML Content

Java Program to get URL details

Java Program to get URL HTML Content

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