//: polymorphism/ReferenceCounting.java
// Cleaning up shared member objects.
import static net.mindview.util.Print.*;  //为将System.out.println() 转换为print()引入的包

class Shared {
  private int refcount = 0;
  private static long counter = 0;
  private final long id = counter++;
  public Shared() {
    print("Creating " + this);
  }
  public void addRef() { refcount++; }
  protected void dispose() {
    if(--refcount == 0)
      print("Disposing " + this);
  }
  public String toString() { return "Shared " + id; }
}

class Composing {
  private Shared shared;
  private static long counter = 0;
  private final long id = counter++;
  public Composing(Shared shared) {
    print("Creating " + this);
    this.shared = shared;
    this.shared.addRef();
  }
  protected void dispose() {
    print("disposing " + this);
    shared.dispose();
  }
  public String toString() { return "Composing " + id; }
}

public class ReferenceCounting {
  public static void main(String[] args) {
    Shared shared = new Shared();
    Composing[] composing = { new Composing(shared),
      new Composing(shared), new Composing(shared),
      new Composing(shared), new Composing(shared) };
    for(Composing c : composing)
      c.dispose();
  }
}

//Output:
Creating Shared 0
Creating Composing 0
Creating Composing 1
Creating Composing 2
Creating Composing 3
Creating Composing 4
disposing Composing 0
disposing Composing 1
disposing Composing 2
disposing Composing 3
disposing Composing 4
Disposing Shared 0
*///:~

//为什么从程序在运行中refcount=5,另外共享对象是什么意思?

java中对象的传递是传引用的，Composing的构造函数中执行了shared的addref方法。将refcount+1了
由于 composing数组中new Composing时传入的对象是同一个shared，所以这个shared的refcount一共加了5次1

换句话说5个Composing对象中的shared所引用的是同一个对象。

如果把

Composing[] composing = { new Composing(shared),
      new Composing(shared), new Composing(shared),
      new Composing(shared), new Composing(shared) };

改成

Composing[] composing = { new Composing(new Shared()),
      new Composing(new Shared()), new Composing(new Shared()),
      new Composing(new Shared()), new Composing(new Shared()) };

那么就有5个Shared对象，每个对象的refcount就是1而不是5了

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