"Non-Static Variable This Cannot Be Referenced from a Static Context" When Creating an Object

Non-static variable this cannot be referenced from a static context when creating an object

Make ShowBike.Bicycle static.

public class ShowBike {

    private static class Bicycle {
        public int gear = 0;
        public Bicycle(int v) {
            gear = v;
        }

    }

    public static void main() {
        Bicycle bike = new Bicycle(5);
        System.out.println(bike.gear);
    }
}

In Java there are two types of nested classes: "Static nested class" and "Inner class". Without the static keyword it is an inner class and you will need an instance of ShowBike to access ShowBike.Bicycle:

ShowBike showBike = new ShowBike();
Bicycle bike = showBike.new Bicycle(5);

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Static nested classes and normal (non-nested) classes are almost the same in functionality, it's just different ways to group things. However, when using static nested classes, you cannot put definitions of them in separated files, which will lead to a single file containing a lot of class definitions.

java: non-static variable this cannot be referenced from a static context

One approach

Declare Man class as static and you'll be able to access it from within main() which is static as well (not tied to any instance of class Solution):

public static class Man

Another approach

We can also leave class Man non-static and create an instance-level factory-method which will create instances of Man:

public class Solution {

    public static void main(String[] args) {
        //create two object of every class here
        Solution solution = new Solution();
        Man m1 = solution.createMan("a1", "b1", 11);
        Man m2 = solution.createMan( "a2", "b2", 12);

        //output them to screen here
        System.out.println(m1.name + " " + m1.age + " " + m1.address);
        System.out.println(m2.name + " " + m2.age + " " + m2.address);    
    }

    Man createMan(String name, String address, int age) {
        return new Man(name, address, age);
    }

    //add your classes here
    public class Man {
        private String name;
        private String address;
        private int age;

        private Man(String name, String address, int age) {
            this.name = name;
            this.address = address;
            this.age = age;
        }
    }
}

non-static variable cannot be referenced from static context [JAVA]

You can't access a non-static variable from a static context.
Your variables(non-static) are outside of main method(static).

Declare your variables as below:

static ArrayList<Spelare> spelare = new ArrayList<>();
static BlackJackKortlek leken = new BlackJackKortlek(4);
static Dealer dealer = new Dealer();

Or declare it inside main:

public static void main(String[] args) {
    ArrayList<Spelare> spelare = new ArrayList<>(); //List with players
    BlackJackKortlek leken = new BlackJackKortlek(4); //BlackJackDeck
    Dealer dealer = new Dealer();
}

Why do I get non-static variable this cannot be referenced from a static context?

Your nested class (which isn't a subclass, by the way) isn't marked as being static, therefore it's an inner class which requires an instance of the encoding class (JavaApp1) in order to construct it.

Options:

• Make the nested class static
• Make it not an inner class (i.e. not within JavaApp1 at all)

• Create an instance of JavaApp1 as the "enclosing instance":

  GenTest x = new JavaApp1().new GenTest();
  

Personally I'd go with the second approach - nested classes in Java have a few oddities around them, so I'd use top-level classes unless you have a good reason to make it nested. (The final option is particularly messy, IMO.)

See section 8.1.3 of the JLS for more information about inner classes.

non-static variable this cannot be referenced from a static context when creating instance of class

You need to make the Edge nested class static:

public static class Edge {
    ...
}

Otherwise, the nested class remains non-static, which means that it retains a reference to the instance of its outer class. As a consequence, only instance methods or other places where you have access to an instance of the outer class can instantiate the inner class.

In general, public static classes are good candidates for top-level classes. The exception is when they are tied to their outer class to the extend that they make no sense outside its context. For example, Map.Entry makes no sense outside its outer Map interface.

Non static field cannot be referenced from a static context- Main method

The main method is static meaning that it belongs to the class and not some object. As such, it a static context cannot reference an instance variable because it wouldn't know what instance of Runner it would use if there even was one.

In short, the solution is to make your Tasks object static in the Runner class.

non-static variable arr cannot be referenced from a static context

Your main method is a static method. It actually exists before any object is created from your class, and thus cannot access instance variables and methods directly. You cannot access non static methods or variables from the same class unless you create an object for the class, i.e Launcher launcher = new Launcher();.

In this case, your player array arr is not static. You either need to make this static or create a Launcher object and access the variable from there. In the latter case, you will need to make the arr array public.

The first option requires you to change your player array declaration to private static Player arr;.

The second requires you to change the access of the arr array to public and access it like so: launcher.arr.

Regarding your second error, you need to either do this: arr = myArray.getPlayerArray();
or just access the array directly like this: myArray.getPlayerArray()[0] (for the first item in that array).

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