Java代码执行顺序-样例

 

class  Insect ... { 
    private int i = 9; 
    int j; 
    Insect()...{ 
        System.out.println("i=" + i + ",j=" + j); 
        j=37; 
    } 
    private static int x1 = print("static Insect.x1.initialized"); 
    public static int print(String s)...{ 
        System.out.println(s);
        return 47;
    }
}  

class  Bettle  extends  Insect ... { 
    private int k = print("Bettle.k initialized"); 
    public Bettle()...{
        System.out.println("k=" + k); 
        System.out.println("j=" + j); 
    } 
    private static int x2=print("static Insect.x2 initialized"); 
    public static void main(String [] args) ...{ 
        System.out.println("Bettle constructor"); 
        Bettle b = new Bettle();
    }
}

运行结果：
static Insect.x1.initialized
static Insect.x2 initialized
Bettle constructor
i=9,j=0
Bettle.k initialized
k=47
j=37

解释：

Bettle运行需要先加载父类Insect,在加载Insect时先运行所有的Static代码,print()函数建立,但不运行.
这一句会运行：private static int x1 = print("static Insect.x1.initialized");
父类加载完成后加载子类Bettle,同样先初始化所有static代码,于是先运行：private static int x2=print("static Insect.x2 initialized");
然后进入main(),运行System.out.println("Bettle constructor");
再运行Bettle b=new Bettle();创建对象时先新建父类,此时先把所有变量设为初始值(i=9,j=0),然后触发父类constructor.
加载完父类再加载子类,同上先设定义值:private int k=print("Bettle.k initialized");然后运行构造函数