Error: non-static method instanceMethod() cannot be referenced from a static context

Question

Problem:

I am very noob in java programming. I was doing my coding practice and wrote this code:

public class StaticDemo {
    int i = 0;
    public static void main(String[] args) {
        System.out.println("in main method which is static");
        // Trying to access non-static field
        i = 5;
        // Trying to access non-static method
        instanceMethod();
    }
    
    public void instanceMethod(){
        System.out.println("Value of i- " + i);
    }
}

but the program gives me he following error message:

Main.java:1: error: class StaticDemo is public, should be declared in a file named StaticDemo.java
public class StaticDemo {
       ^
Main.java:6: error: non-static variable i cannot be referenced from a static context
        i = 5;
        ^
Main.java:8: error: non-static method instanceMethod() cannot be referenced from a static context
        instanceMethod();
        ^
3 errors

Can anyone help me out to fix this problem? 

Answer 1

In your code you need to declare the instance variables static or you should refer them using an object in the method, so you should try like this:

public class StaticDemo {
    int i = 0;
    public static void main(String[] args) {
        System.out.println("in main method which is static");
        StaticDemo obj = new StaticDemo();
        obj.i = 5;
        obj.instanceMethod();
    }
    
    public void instanceMethod(){
        System.out.println("Value of i- " + i);
    }
}

Hope this help you.