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1.初始化的顺序
对类而言,初始化的顺序是由变量在类的定义里面的顺序决定的,变量的定义可能会分散在类定义的各个地方,并且与方法的定义相互交错,但是变量的初始化会先于任何方法,甚至是构造函数的调用。
class Tag {
Tag(int marker) {
System.out.println("Tag(" + marker + ")");
}
}
class Card {
Tag t1 = new Tag(1); // Before constructor
Card() {
// Indicate we're in the constructor:
System.out.println("Card()");
t3 = new Tag(33); // Reinitialize t3
}
Tag t2 = new Tag(2); // After constructor
void f() {
System.out.println("f()");
}
Tag t3 = new Tag(3); // At end
}
public class Flower {
public static void main(String[] args) {
Card t = new Card();
t.f(); // Shows that construction is done
}
}
输出结果如下:
Tag(1)
Tag(2)
Tag(3)
Card()
Tag(33)
f()
2.静态数据的初始化
无论创建多少对象,static数据只能有一份。它的初始化不是在定义的时候进行的。
class Bowl {
Bowl(int marker) {
System.out.println("Bowl(" + marker + ")");
}
void f(int marker) {
System.out.println("f(" + marker + ")");
}
}
class Table {
static Bowl b1 = new Bowl(1);
Table() {
System.out.println("Table()");
b2.f(1);
}
void f2(int marker) {
System.out.println("f2(" + marker + ")");
}
static Bowl b2 = new Bowl(2);
}
class Cupboard {
Bowl b3 = new Bowl(3);
static Bowl b4 = new Bowl(4);
Cupboard() {
System.out.println("Cupboard()");
b4.f(2);
}
void f3(int marker) {
System.out.println("f3(" + marker + ")");
}
static Bowl b5 = new Bowl(5);
}
public class E1 {
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();
Table t2 = new Table();
Cupboard t3 = new Cupboard();
t2.f2(1);
t3.f3(1);
}
}
程序的输出如下:
Creating new Cupboard() in main
Bowl(4)
Bowl(5)
Bowl(3)
Cupboard()
f(2)
Creating new Cupboard() in main
Bowl(3)
Cupboard()
f(2)
Bowl(1)
Bowl(2)
Table()
f(1)
Bowl(3)
Cupboard()
f(2)
f2(1)
f3(1)
从程序的输出可以看出,static成员只会在需要的时候进行初始化。如果没有创建Table对象,就永远不可能用到Table.b1或者Table.b2,因此也不会去创建static的Bowl b1和b2。只有创建了第一个Table对象之后(或者第一次访问static成员的时候),它们才会被初始化。此后,static对象就不会再作初始化了。
本文来自ChinaUnix博客,如果查看原文请点:http://blog.chinaunix.net/u/19013/showart_112541.html |
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