Where is the initialization of static and non-static fields allowed?

In Java, initialization of static and non-static fields is allowed in different places:

• Static fields (static):

  • Can be initialized directly at the declaration in the class.
  • Can also be initialized in static initialization blocks (static { ... }).

• Non-static fields (instance):

  • Can be initialized at the declaration in the class.
  • Can be initialized in the class constructor.
  • Can be initialized in non-static initialization blocks ({ ... }).

Example:

public class Example {
    static int staticField = 10; // initialization at declaration
    int instanceField = 5;       // initialization at declaration

    static {
        staticField = 20;        // static initialization block
    }

    {
        instanceField = 15;      // non-static initialization block
    }

    public Example() {
        instanceField = 25;      // initialization in constructor
    }
}

Thus, static fields are initialized once when the class is loaded, while non-static fields are initialized each time an object is created.