Following are examples of variable declaration and initialization in Java.
Example:
int x, y, z; // Declares three ints, x, y, and z. int x = 10, y = 25; // Example of initialization byte Y = 24; // initializes a byte type variable Y. double pi = 3.14159; // declares and assigns a value of PI. char x = 'x'; // the char variable a iis initialized with value 'x'
Three type of variable:
- Local variables
- Instance variables
- Class/Static variables
Local Variables
- Access modifiers cannot be used for local variables.
- Local variables are declared in methods, constructors, or blocks.
- Local variables are visible only within the declared method, constructor, or block.
Example:
public class Test {
public void pupAge() {
int age = 0;
age = age + 9;
System.out.println("Puss age is : " + age);
}
public static void main(String args[]) {
Test test = new Test();
test.pupAge();
}
} output
Puss age is: 9
Following example uses age without initializing it, so it would give an error at the time of compilation.
public class Test {
public void pupAge() {
int age;
age = age + 9;
System.out.println("Puss age is : " + age);
}
public static void main(String args[]) {
Test test = new Test();
test.pupAge();
}
} Output
/Test.java:4: error: variable age might not have been initialized
age = age + 9;
^
1 error Instance Variables
- Access modifiers can be given for instance variables.
- Instance variables can be accessed directly by calling the variable name inside the class.
- Values can be assigned during the declaration or within the constructor.
import java.io.*;
public class Student {
// this instance variable is visible for any child class.
public String name;
// salary variable is visible in Student class only.
private double salary;
// The name variable is assigned in the constructor.
public Student (String empName) {
name = empName;
}
// The salary variable is assigned a value.
public void setSalary(double empSal) {
salary = empSal;
}
// This method prints the Student details.
public void printEmp() {
System.out.println("name : " + name );
System.out.println("salary :" + salary);
}
public static void main(String args[]) {
Student empOne = new Student("Nicki Minaj");
empOne.setSalary(50000);
empOne.printEmp();
}
} output
name : Nicki Minaj salary :50000.0
Class/Static Variables
- Static variables are stored in the static memory
- tatic variables are created when the program starts and destroyed when the program stops.
- Static variables can be accessed by calling with the class name ClassName.VariableName.
import java.io.*;
public class Employee {
// salary variable is a private static variable
private static double salary;
// developer is a constant
public static final String developer = "job ";
public static void main(String args[]) {
salary = 83000;
System.out.println(developer + "average salary:" + salary);
}
} output
job average salary:83000.0