class SecondClass {
    static FirstClass fc1 = new FirstClass(1);
    FirstClass fc3 = new FirstClass(3);
    static {
        FirstClass fc2 = new FirstClass(2);
    }
   
    {
        System.out.println("SecondClass's block, this block is not static block.");
    }
   
    SecondClass() {
        System.out.println("SecondClass()");
    }
   
    FirstClass fc4 = new FirstClass(4);
}

public class InitiationDemo {
    SecondClass sc1 = new SecondClass();
   
    {
        System.out.println("Hello Java World!");
    }
   
    public static void main(String[] args) {
        System.out.println("Inside main()");
        SecondClass.fc1.useMethod(100);
        InitiationDemo idObj = new InitiationDemo();
    }
   
    static SecondClass sc2 = new SecondClass();
}

运行结果:

FirstClass(1)
FirstClass(2)
FirstClass(3)
SecondClass's block, this block is not static block.
FirstClass(4)
SecondClass()
Inside main()
useMethod(100)
FirstClass(3)
SecondClass's block, this block is not static block.
FirstClass(4)
SecondClass()
Hello Java World!