java继承和finalize()
时间:2007-05-28 yycnet.yeah.net yyc译
通过“合成”方法创建新类时，永远不必担心对那个类的成员对象的收尾工作。每个成员都是一个独立的对象，所以会得到正常的垃圾收集以及收尾处理——无论它是不是不自己某个类一个成员。但在进行初始化的时候，必须覆盖衍生类中的finalize()方法——如果已经设计了某个特殊的清除进程，要求它必须作为垃圾收集的一部分进行。覆盖衍生类的finalize()时，务必记住调用finalize()的基础类版本。否则，基础类的初始化根本不会发生。下面这个例子便是明证：
//: Frog.java
// Testing finalize with inheritance
class DoBaseFinalization {
public static boolean flag = false;
}
class Characteristic {
String s;
Characteristic(String c) {
s = c;
System.out.println(
"Creating Characteristic " + s);
}
protected void finalize() {
System.out.println(
"finalizing Characteristic " + s);
}
}
class LivingCreature {
Characteristic p =
new Characteristic("is alive");
LivingCreature() {
System.out.println("LivingCreature()");
}
protected void finalize() {
System.out.println(
"LivingCreature finalize");
// Call base-class version LAST!
if(DoBaseFinalization.flag)
try {
super.finalize();
} catch(Throwable t) {}
}
}
class Animal extends LivingCreature {
Characteristic p =
new Characteristic("has heart");
Animal() {
System.out.println("Animal()");
}
protected void finalize() {
System.out.println("Animal finalize");
if(DoBaseFinalization.flag)
try {
super.finalize();
} catch(Throwable t) {}
}
}
class Amphibian extends Animal {
Characteristic p =
new Characteristic("can live in water");
Amphibian() {
System.out.println("Amphibian()");
}
protected void finalize() {
System.out.println("Amphibian finalize");
if(DoBaseFinalization.flag)
try {
super.finalize();
} catch(Throwable t) {}
}
}
public class Frog extends Amphibian {
Frog() {
System.out.println("Frog()");
}
protected void finalize() {
System.out.println("Frog finalize");
if(DoBaseFinalization.flag)
try {
super.finalize();
} catch(Throwable t) {}
}
public static void main(String[] args) {
if(args.length != 0 &&
args[0].equals("finalize"))
DoBaseFinalization.flag = true;
else
System.out.println("not finalizing bases");
new Frog(); // Instantly becomes garbage
System.out.println("bye!");
// Must do this to guarantee that all
// finalizers will be called:
System.runFinalizersOnExit(true);
}
} ///:~
DoBasefinalization类只是简单地容纳了一个标志，向分级结构中的每个类指出是否应调用super.finalize()。这个标志的设置建立在命令行参数的基础上，所以能够在进行和不进行基础类收尾工作的前提下查看行为。分级结构中的每个类也包含了Chara |
