类初始化顺序问题，final修饰属性影响加载顺序

测试1：

public class Demo{
    public Demo(){
        System.out.println("create demo object");
    }
    public static String str = "abcd";
    static {
        System.out.println("init static block.");
    }
}

public class Test1{
    public static void main(String... args){
        String a = Demo.str;
        System.out.println(a);
    }
}

结果1：

init static block.
abcd

---

---

测试2：

public class Demo2{
    public Demo(){
        System.out.println("create demo object");
    }
    public static final String str = "abcd";
    static {
        System.out.println("init static block.");
    }
}

public class Test2{
    public static void main(String... args){
        String a = Demo.str;
        System.out.println(a);
    }
}

结果2：

abcd

---

---

测试3：

public class Demo3{
    public Demo(){
        System.out.println("create demo object");
    }
    public static final String str = new String("abcd");
    static {
        System.out.println("init static block.");
    }
}

public class Test3{
    public static void main(String... args){
        String a = Demo.str;
        System.out.println(a);
    }
}

结果3：
编译时候不能确认a值，只有在运行时才赋予a值

init static block.
abcd

问题：
有final和没有final修饰，初始化不一样，怎么理解？？