在类的内部，变量定义的先后顺序决定了初始化的顺序，并且都在任何方法（包括构造方法）前初始化
class Window{
public Window(int marker){
System.out.println("Window(" + marker + ")");
}
}
class House{
Window w1 = new Window(1);
public House(){
System.out.println("House()");
w3 = new Window(33);
}
Window w2 = new Window(2);
void f(){
System.out.print("f()");
}
Window w3 = new Window(3);
}
public class Main {
public static void main(String[] args) throws InterruptedException {
House h = new House();
h.f();
}
}
运行结果：
如果类中有静态变量（static），那么静态数据会先与非静态变量，并且一个类的static变量在只会在第一次被初始化一次。如果没有对静态变量进行初始化，那么静态变量采用基本类型的标准初值，如果是对象引用，则为null
class Bowl{
Bowl(int marker){
System.out.println("Bowl(" + marker + ")");
}
void f1(int marker){
System.out.println("f1(" + marker + ")");
}
}
class table{
static Bowl bowl1= new Bowl(1);
public table(){
System.out.println("table()");
bowl2.f1(1);
}
void f2(int marker){
System.out.println("f2(" + marker + ")");
}
static Bowl bowl2 = new Bowl(2);
}
class cupboard{
Bowl bowl3 = new Bowl(3);
static Bowl bowl4 = new Bowl(4);
cupboard(){
System.out.println("cupboard");
bowl4.f1(2);
}
void f3(int marker){
System.out.println("f3(" + marker + ")");
}
static Bowl bowl5 = new Bowl(5);
}
public class Main {
public static void main(String[] args) throws InterruptedException {
System.out.println("Creating new cupboard() in main");
new cupboard();
System.out.println("Creating new cupboard() in main");
new cupboard();
t.f2(1);
c.f3(1);
}
static table t = new table();
static cupboard c = new cupboard();
}
运行结果：
对于静态变量，可以通过类直接调用。因此，当从未生成类的对象，类直接调用静态变量，则该类的静态变量都会被初始化
class cup{
cup(int marker){
System.out.println("cup(" + marker + ")");
}
public void f(int marker){
System.out.println("f(" + marker + ")");
}
}
class cups{
static cup c1;
static cup c2;
static {
c1 = new cup(1);
c2 = new cup(2);
}
cups(){
System.out.println("cups()");
}
}
public class Main {
public static void main(String[] args) throws InterruptedException {
System.out.println("Inside main()");
cups.c1.f(99);
}
}
运行结果：
对于非静态块，每次创建对象，都会被初始化
class mug{
mug(int marker){
System.out.println("mug(" + marker + ")");
}
public void f(int marker){
System.out.println("f(" + marker + ")");
}
}
class mugs{
mug mug1;
mug mug2;
{
mug1 = new mug(1);
mug2 = new mug(2);
System.out.println("mug1 & mug2 finish");
}
mugs(){
System.out.println("mugs()");
}
mugs(int i){
System.out.println("mugs(int)");
}
}
public class Main {
public static void main(String[] args) throws InterruptedException {
System.out.println("Inside main");
new mugs();
System.out.println("new mugs() completed");
new mugs(1);
System.out.println("new mugs(1) completed");
}
}
结论：
1） 对于类中变量的初始化，执行顺序：静态变量>非静态变量>构造方法
2）即使当类没有定义对象时，通过类去调用静态变量，静态变量都会被初始化
3）静态变量为类变量，只会被初始化一次
