静态数据的初始化

静态数据的初始化

如果数据属于某个基本类型，而且也没有对它进行初始化，那么它就会获得基本类型的标准初值；如果它是一个对象引用，那么除非心创建一个对象，并指派给该引用，否则它就是空值（null）

无论创建多少个对象，静态数据都只占用一份存储区域。

//4.4.2.1 public class StaticInitialization {     public static void main(String[] args) {        System.out.println("Creating new Cupboard() in main");        new Cupboard();        System.out.println("Creating new Cupboard() in main");        new Cupboard();        t2.f2(1);        t3.f3(1);     }     static Table t2 = new Table();     static Cupboard t3 = new Cupboard(); } class Bow1 {     Bow1(int marker)     {        System.out.println("Bow1(" + marker + ")");     }     void f(int marker)     {         System.out.println("f(" + marker + ")");     } } class Table {     static Bow1 b1 = new Bow1(1);     Table()     {        System.out.println("Table()");        b2.f(1);     }     void f2(int marker)     {        System.out.println("f2(" + marker + ")");     }     static Bow1 b2 = new Bow1(2); } class Cupboard {     Bow1 b3 = new Bow1(3);     static Bow1 b4 = new Bow1(4);     Cupboard()     {        System.out.println("Cupboard()");        b4.f(2);     }     void f3(int marker)     {        System.out.println("f3(" + marker + ")");     }     static Bow1 b5 = new Bow1(5); }

输出结果：

Bow1(1)

Bow1(2)

Table()

f(1)

Bow1(4)

Bow1(5)

Bow1(3)

Cupboard()

f(2)

Creating new Cupboard() in main

Bow1(3)

Cupboard()

f(2)

Creating new Cupboard() in main

Bow1(3)

Cupboard()

f(2)

f2(1)

f3(1)

静态块

//4.4.2—think in java public class ExplicitStatic {     public static void main(String[] args) {        System.out.println("Inside main()");        Cups.c1.f(99);     } } class Cup {     Cup(int marker)     {        System.out.println("Cup(" + marker + ")");     }     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()");     } }

输出结果：

Inside main()

Cup(1)

Cup(2)

f(99)

public class Test {     static int i = 1;     static     {        i++;     }     public Test()     {        i++;     }       public static void main(String[] args)     {        Test t1 = new Test();        System.out.println(t1.i); //1          Test t2 = new Test();        System.out.println(t2.i); //2        } }

输出结果：

3

4

 

非静态实例初始化

public class Mugs {     Mug c1;     Mug c2;     {        c1 = new Mug(1);        c2 = new Mug(2);        System.out.println("c1 & c2 initialized");     }     Mugs()     {        System.out.println("Mugs()");     }     public static void main(String[] args) {        System.out.println("Inside main()");        Mugs x = new Mugs();     } } class Mug {     Mug(int marker)     {        System.out.println("Mug(" + marker + ")");     }     void f(int marker)     {        System.out.println("f(" + marker + ")");     } }

输出结果：

Inside main()

Mug(1)

Mug(2)

c1 & c2 initialized

Mugs()