Java代码块

public class ConstructorTest1 {
    {//构造代码块
        System.out.println("执行构造代码块");
    }

    public ConstructorTest1() {
        System.out.println("执行无参构造函数");
    }

    public ConstructorTest1(String string) {
        System.out.println("执行有参构造函数");
    }

    public static void main(String[] args) {
        new HelloB();
        new ConstructorTest1();
        new ConstructorTest1("con");
    }
}

class HelloB extends HelloA {
    public HelloB() {
        System.out.println("HelloB");
    }
    {
        System.out.println("I'm B class");
    }
    static {
        System.out.println("static B");
    }
}

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

输出结果：

static A
static B
I'm A class
HelloA
I'm B class
HelloB
执行构造代码块
执行无参构造函数
执行构造代码块
执行有参构造函数