frog.java

Java编程思想 第七课 全源码

//: c07:Frog.java
// From 'Thinking in Java, 2nd ed.' by Bruce Eckel
// www.BruceEckel.com. See copyright notice in CopyRight.txt.
// 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() throws Throwable {
    System.out.println(
      "LivingCreature finalize");
    // Call base-class version LAST!
    if(DoBaseFinalization.flag)
      super.finalize();
  }
}

class Animal extends LivingCreature {
  Characteristic p = 
    new Characteristic("has heart");
  Animal() {
    System.out.println("Animal()");
  }
  protected void finalize() throws Throwable {
    System.out.println("Animal finalize");
    if(DoBaseFinalization.flag)
      super.finalize();
  }
}

class Amphibian extends Animal {
  Characteristic p = 
    new Characteristic("can live in water");
  Amphibian() {
    System.out.println("Amphibian()");
  }
  protected void finalize() throws Throwable {
    System.out.println("Amphibian finalize");
    if(DoBaseFinalization.flag)
      super.finalize();
  }
}

public class Frog extends Amphibian {
  Frog() {
    System.out.println("Frog()");
  }
  protected void finalize() throws Throwable {
    System.out.println("Frog finalize");
    if(DoBaseFinalization.flag)
      super.finalize();
  }
  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!");
    // Force finalizers to be called:
    System.gc();
  }
} ///:~