成员初始化的先后顺序

ClassLoaderDemo.java:

package test;

class SuperLoader {
int i = setI();
static int j = setJ();
int z;
SuperLoader() {
System.out.println("SuperLoader @ constructor @ z 2 initialized.");
this.z = 5;
}
public int setI() {
System.out.println("SuperLoader @ i @ initialized.");
return 10;
}
public static int setJ() {
System.out.println("SuperLoader @ j @ initialized.");
return 15;
}
}

public class ClassLoaderDemo extends SuperLoader {
int a = setA();
static int b = setB();
int c;
ClassLoaderDemo() {
System.out.println("ClassLoaderDemo @ constructor @ c @ initialized.");
this.c = 0;
}
public int setA() {
System.out.println("ClassLoaderDemo @ a @ initialized.");
return 20;
}
public static int setB() {
System.out.println("ClassLoaderDemo @ b @ initialized.");
return 25;
}
public static void main(String[] args) {
ClassLoaderDemo cld = new ClassLoaderDemo();
}
}

结果：

SuperLoader @ j @ initialized.
ClassLoaderDemo @ b @ initialized.
SuperLoader @ i @ initialized.
SuperLoader @ constructor @ z 2 initialized.
ClassLoaderDemo @ a @ initialized.
ClassLoaderDemo @ constructor @ c @ initialized.

分析：

一、开始装载ClassLoaderDemo类时，发现它有父类SuperLoader。于是先装载SuperLoader,发现该类有静态变量j，对其进行初始化，完成装载。

二、完成对SuperLoader类的装载后，再回过头来装载ClassLoaderDemo,发现它有静态变量b，对其进行初始化，完成装载。

三、开始创建ClassLoaderDemo类的一个实例，为其分配内存空间。发现它有父类SuperLoader，先对父类进行初始化。先初始化实例变量i，然后调用父类的构造函数对变量z进行初始化。完成父类初始化。

四，父类初始化完毕后，依例对ClassLoaderDemo进行初始化。