Getting access to class properties from within class methods - Java

Question

I have the following code:

public class UserRepository 
{       
    private MyDataSource myDataSource = new MyDataSource();

    public static User CreateUser( int id, String firstName, String lastName )
    {
         myDataSource.propertyOfThis...
         // myDataSource is not accessible and yet i have declared it as a property of UserRespository?
    }
...

What am i missing here?

Answer 1

myDataSource is not static

private MyDataSource myDataSource = new MyDataSource();

But CreateUser is static

public static User CreateUser( int id, String firstName, String lastName )

So make myDataSource static or remove CreateUser 's static modifier.

Oh, or a new UserRepository() .

Answer 2

You need to make myDataSource as static. Static method can be called without creating an instance and as myDataSource is an instance variable hence it is not accessible.

Answer 3

您的方法CreateUser是静态的，而MyDataSource是实例字段

Answer 4

The problem is that your field is not static , and yet you are using it in a static method.

The problem is that static methods are not executed on an instance of a class (object), but on the class itself. A field exists only in an object. Hence the method needs not to be static, or field should be static. Depends on your use case.

Answer 5

You method is static . As has been stated already, you cannot access non-static methods or variables from within a static method.

The reason for this is that static members and methods are accessible without the class being instantiated. However, those non-static (aka "instance") variables belong to a particular INSTANCE of that class. Therefore you have to have an instantiated object to reference in order to get the variables.

If you are in a static block of code, then you cannot use the keyword this for the same reason. this refers to a particular instantiated object of that class.

Answer 6

* The problem is that your field is not static, and yet you are using it in a static method. *The problem is that static methods are not executed on an instance of a class (object), but on the class itself.