public class StaticInit1 { StaticInit1(){ System.out.println("StaticInit_1_init"); } StaticInit1(int i){ System.out.println("StaticInit_1_init,int i ="+i); } }
public class StaticInit { StaticInit1 s2 = new StaticInit1(1); public StaticInit() { System.out.println("StaticInit-init"); } static StaticInit1 s1 = new StaticInit1(); public static void main(String[] args) { new StaticInit(); /* output: StaticInit_1_init StaticInit_1_init,int i =1 StaticInit-init */ } }
根据输出结果,可以发现
在初始化 StaticInit类时,先初始化了类的静态变量. 再是执行了变量s2的初始化,最后 才是类构造器的执行输出
对StaticInit类再加一个f()方法
public class StaticInit { StaticInit1 s2 = new StaticInit1(1); public StaticInit() { System.out.println("StaticInit-init"); } static StaticInit1 s1 = new StaticInit1(); void f(){ new StaticInit(); } public static void main(String[] args) { new StaticInit().f(); /* output: StaticInit_1_init StaticInit_1_init,int i =1 StaticInit-init StaticInit_1_init,int i =1 StaticInit-init */ } }
查看输出结果 , 通过f()方法再次(第二次执行)创建Staticinit类时,初始化类时并未执行静态变量的初始化,也就是说 :静态变量的初始化只执行一次.
Next Example
public class Window { Window(int i){ System.out.println("Window==i="+i); } }
public class House { Window w1 = new Window(1); House(){ System.out.println("house"); w3 = new Window(33); } Window w2 = new Window(2); void walk(){ System.out.println("walk"); } Window w3 = new Window(3); }
public class OrderOfInit { public static void main(String[] args) { House house = new House(); house.walk(); } /* Output: Window==i=1 Window==i=2 Window==i=3 house Window==i=33 walk */ }
静态数据初始化
public class Bowl { Bowl(int i) { print("Bowl->i="+i); } void f1(int i){ print("f1->i="+i); } }
public class Table { static Bowl b1 = new Bowl(1); Table(){ print("Table"); } Bowl b3 = new Bowl(3); void f2(int i){ print("f2->i="+i); } static Bowl b2 = new Bowl(2); }
public class Cupboard { Bowl b4 = new Bowl(4); static Bowl b5 = new Bowl(5); Cupboard(){ print("cupboard"); b4.f1(2); } void f3(int i){ print("f3->i="+i); } static Bowl b6 = new Bowl(6); }
public class StaticInit { public static void main(String[] args) { new Cupboard(); new Cupboard(); table.f2(1); cupboard.f3(1); } static Table table = new Table(); static Table table1 = new Table(); static Cupboard cupboard = new Cupboard(); /*Output: 产生输出对应的语句 Bowl->i=1 Bowl->i=2 static Table table = new Table(); Bowl->i=3 Table ----------- Bowl->i=3 static Table table1 = new Table(); Table ----------- Bowl->i=5 Bowl->i=6 Bowl->i=4 static Cupboard cupboard = new Cupboard(); cupboard f1->i=2 ----------- Bowl->i=4 cupboard new Cupboard(); f1->i=2 ----------- Bowl->i=4 cupboard new Cupboard(); f1->i=2 ----------- f2->i=1 table.f2(1); f3->i=1 cupboard.f3(1); */ }
封装System.out.println输出语句
只能打印字符串…
public class Print { public static void print(String something){ System.out.println(something); } }
以静态方式引入
import static edu.Print.print;
