java代码执行顺序

class HelloA {

    public HelloA() {
        System.out.println("HelloA");
    }

    { System.out.println("I'm A class"); }

    static { System.out.println("static A"); }

}

public class HelloB extends HelloA {
    public HelloB() {
        System.out.println("HelloB");
    }

    { System.out.println("I'm B class"); }

    static { System.out.println("static B"); }

    public static void main(String[] args) {

        System.out.println("-------main start-------");
        new HelloB();
        new HelloB();
        System.out.println("-------main end-------");
    }
}

输出的结果：

static A
static B
-------main start-------
I'm A class
HelloA
I'm B class
HelloB
I'm A class
HelloA
I'm B class
HelloB
-------main end-------

public class HelloA {

    public HelloA() {
        System.out.println("HelloA");
    }

    {
        System.out.println("I'm A class");
    }

    static {
        System.out.println("static A");
    }
}

public class HelloB extends HelloA {

    private HelloB() {
        System.out.println("HelloB");
    }

    public static HelloB getInstance(){
        return TestHolder.instance;
    }

    {
        System.out.println("I'm B class");
    }

    static {
        System.out.println("static B");
    }

    public static void main(String[] args) {
        System.out.println("-------main start-------");
//        new Test();
//        new Test();
        HelloB.getInstance();
        HelloB.getInstance();

        System.out.println("-------main end-------");
    }

    public static class TestHolder{
        static {
            System.out.println("static TestHolder");
        }

        {
            System.out.println(" TestHolder.................");
        }
        public static HelloB instance =new HelloB();
    }
}

输出：

static A
static B
-------main start-------
static TestHolder
I'm A class
HelloA
I'm B class
HelloB
-------main end-------