java对象实例化过程中的代码执行顺序

java对象实例化过程中的代码执行顺序

1、执行顺序

（1）执行父类静态的内容，父类静态的内容执行完毕后，接着去执行子类的静态的内容；
（2）子类的静态内容执行完毕之后，初始化父类的成员变量--->执行父类的非静态语  
     句块--->执行父类的构造方法。
（3）父类的构造方法执行完毕之后，初始化子类的成员变量--->执行子类的非静态语
     句块--->执行子类的构造方法。

2、例证

(1)Base.java

public class Base{

public String whenAmISet = "set when declared in parent class";

    Base() {
        System.out.println("4 parent Constructor , it will invoke 
 preProcess() from child class.");
        preProcess(); //调用子类的preProcess;
    }

void preProcess() {}
//静态语句块
static {
        System.out.println("1 parent static block ");   
    }
//非静态语句块
    {
        System.out.println("3 parent dynamic block , after 
 initialized filed from parent class,");
    }
}

(2)Derived.java

public class Derived extends Base
{
public String whenAmISet = "set when declared";

@Override void preProcess()
    {
        whenAmISet = "set in preProcess()";
    }

    Derived() {
        System.out.println("6 child constructor ");
    }

static {

        System.out.println("2 child static block");
    }

    {
        System.out.println("5 child dynamic block , after 
 initialized filed from child class.");
    }    
}

(3)Main.java

public class Main
{
public static void main(String[] args)
    {
        Derived d = new Derived();
        System.out.println( d.whenAmISet );
    }
}

输出：
1 parent static block
2 child static block
3 parent dynamic block , after initialized filed from parent class,
4 parent Constructor , it will invoke preProcess() from child class.
5 child dynamic block , after initialized filed from child class.
6 child constructor
set when declared

提示：想观察执行顺序，可在eclipse选用debug模式，在每行代码输出处打断点观察执行顺序。

参考资料：
(1)Java 静态语句块、语句块、构造函数执行顺序
http://www.cnblogs.com/jycboy/p/5257615.html