Java 初始化及類的加載

下面是Think in Java中的一段代碼，自己加了幾行

package reusing;

import static net.mindview.util.Print.*;

class Insect {
 private int i = 9;
 protected int j;
 
 private int x2 = printInit("Insect.x1 initialized");

 Insect() {
  print("i = " + i + ", j = " + j);
  j = 39;
 }
 static {
  System.out.println("Init Static block");
 }
 
 {
  System.out.println("Init block");
 }

 private static int x1 = printInit("static Insect.x1 initialized");

 static int printInit(String s) {
  print(s);
  return 47;
 }
}

public class Beetle extends Insect {
 private int k = printInit("Beetle.k initialized");
 
 static {
  System.out.println("Beetle static block");
 }

 public Beetle() {
  print("k = " + k);
  print("j = " + j);
 }

 private static int x2 = printInit("static Beetle.x2 initialized");
 private int x1 = printInit("Beetle.x2 initialized");

 
 public static void main(String[] args) {
  print("Beetle constructor");
  Beetle b = new Beetle();
 }
 
}

分析其類加載的過程：

（1）首先加載當前類，再加載當前類的父類，直到加載到基類，然後執行基類的static代碼塊，再執給基類裡面的static成員變量賦值，賦值完成之後再執行子類裡面的static代碼塊和給static成員變量賦值，以此類推。

（2）static塊和成員賦值為完成之後回到基類中，給其余的非static的成員變量賦值，再執行非靜態塊，然後是構造方法，完成之後回到子類中繼續按（2）處執行

上面的代碼執行結果是：

Init Static block
static Insect.x1 initialized
Beetle static block
static Beetle.x2 initialized
Beetle constructor
Insect.x1 initialized
Init block
i = 9, j = 0
Beetle.k initialized
Beetle.x2 initialized
k = 47
j = 39