Hey guys in this quick post, we will discuss different types of variables in Java programming with examples
Table of Contents
Overview
Variables is just a placeholder or container to store the data, it can be changed during the program execution.
There are 3 different types of variables:
- Instance variables
- Static variables
- Local variables
Instance variables
- Instance variables are declared inside the class but outside the method
public class Test {
int a = 10;
public void m1() {
//TODO
}
}
- Instance variables cannot be accessed directly inside the static method or block
public class Test {
int a = 10;
public static void main(String[] args) {
System.out.println(a); //compilation error
}
}
- We can access the instance variables inside static method using Object reference
public class Test {
int a = 10;
public static void main(String[] args) {
Test t = new Test();
System.out.println(t.a); //10
}
}
- Initialization is optional for instance variables, JVM will provide the default values
public class Test {
int a;
String b;
boolean c;
public static void main(String[] args) {
Test t = new Test();
System.out.println(t.a); //0
System.out.println(t.b); //null
System.out.println(t.c); //false
}
}
Static variables
- Static variables are also called as class level variables. Hence we cannot create static variables inside methods
public class Test {
public void m1() {
static int a = 10; //compilation error
}
}
- It creates a single copy for every object and that copy will be shared by all objects of that class
public class Test {
static int a = 10;
public static void main(String[] args) {
Test t1 = new Test();
System.out.println(t1.a); //10
Test t2 = new Test();
System.out.println(t2.a); //10
}
}
- Static variables can be accessed directly by using class name
public class Test {
static int a = 10;
public static void main(String[] args) {
System.out.println(Test.a); //10
}
}
- Just like instance variables, initialization is optional for static variables as well, JVM will provide the default values
public class Test {
static int a;
static boolean b;
static String c;
public static void main(String[] args) {
System.out.println(Test.a); //0
System.out.println(Test.b); //false
System.out.println(Test.c); //null
}
}
Local variables
- Local variables are also called as temporary variables
- Local variables are created inside the method or block or constructor
public class Test {
public Test() {
int b = 10;
}
public void m1() {
int a = 10;
}
}
- The scope of the local variables is exactly same as the block in which we declared it.
public class Test {
public static void main(String[] args) {
int sum = 0;
for (int i = 0; i < 5; i++) {
sum = sum + i;
}
System.out.println(sum);
System.out.println(i); //compilation error
}
}
- For the local variables, we should initialize the default values before using it
public class Test {
public static void main(String[] args) {
int a;
System.out.println(a); //compilation error
a = 10;
System.out.println(a); //10
}
}
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