Calling the classes in java and accessing the variables

Question

I'm having an issue calling a class in the correct way. I have created a second class called "Questions" and I have created an instance of it under my main class like below:

Questions QuestionBank = new Questions ();

I expected to access all my variables from Questions as QuestionBank.Score, however when I do this QuestionBank is highlighted in red. Questions.Score works fine but doesn't match the instructions I have used.

Any thoughts?

Thank you in advance.

Hi, depends on the visibility of the fields- [public, private or protected](https://stackoverflow.com/questions/215497/in-java-difference-between-package-private-public-protected-and-private) if fields are public, then you should be able to access like you expecting- `instanceName.variableName`, but its not so safe. If you want to have "shared" class variable, then you can mark it as `public static` and you will be able to access by `ClassName.variableName`, btw `due the convention instances should start lowercase` — xxxvodnikxxx, May 04 '18 at 12:18

score 2 · Answer 1 · answered May 04 '18 at 11:55

2

Since your question is pretty vague and difficult to understand, I feel this can be a very good understanding guide for you to understand.

Let me know of you have any problems. :)

answered May 04 '18 at 11:55

Aashish Chaubey

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1
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Swift · Answer 2 · 2018-05-04T15:44:27.897

Questions.Score works fine

That is likely because you have declared your score static

public static int Score;

This means the Score variable belongs to the Questions class itself and there is only one of it. No matter how many times you do new Questions() to create a new instance, there will only be one Score variable which belongs to the Questions class and not instances of the Questions class. This explains why you can only access Score by Questions.Score and not QuestionBank.Score.

To solve this simply remove the static modifier.

public int Score;

Read up on What does the 'static' keyword do in a class?.

score 0 · Answer 3 · answered May 04 '18 at 12:30

start with the look of java visibility

Let me say you will class like this

public class VariableAccessibility {
    public static int STATICVARIABLE = 1;
    public static final int STATICVARIABLECONSTANT = 1;


    int protectedVariable = 1; //protected is default
    public int publicVariable = 1;
    private int privateVariable = 1;

    public int getPrivateVariable() {
        return privateVariable;
    }
    public void setPrivateVariable(int privateVariable) {
        this.privateVariable = privateVariable;
    }
}

Then you can / cannot to do following

VariableAccessibility varAccess = new VariableAccessibility();
int value = varAccess.publicVariable;   //works because its public variable
int staticVariable = varAccess.STATICVARIABLE; //works
int consVar = varAccess.STATICVARIABLECONSTANT; //works, because its static

//int privateVar = varAccess.privateVariable; //not visible
int privateVar = varAccess.getPrivateVariable(); //works, call "getter" will be operating with private class variable

//static variables values modification VariableAccessibility.STATICVARIABLE = 5; //you can do, because static but not final //VariableAccessibility.STATICVARIABLECONSTANT = 5; //cannot to do, because its final

Basically, its a good point to have all what is possible marked as private (with private modifier) and if needed, then create/generate getters and setters (methods with get / set in the name).

public variables are visible everywhere and you can modify them straightly.
private are not visible without getters/setters, protected should be visible in the same package scope.

static and final are having special purpose:

static variables are "shared" cross all instances
final are not modifiable, in general.

Calling the classes in java and accessing the variables

3 Answers3