阿Q:革命了，革命了！（也谈IOC的好处）

// Dependent Component
public interface BIntf {
  void doSomething();;
}
public class BImpl implements BIntf {
  public void doSomething(); {
    // do something here.
  }
}

// Component A using B
// 1. without IoC, direct create
public class A {
  public void doSomething(); {
    BIntf b;  // dependency #1, with BIntf
    b = new BImpl();;  // dependency #2, with BImpl
    b.doSomething();;
  }
}

// 2. without IoC, using customized factory
public class A {
  public void doSomething(); {
    BIntf b;  // dependency #1, with BIntf
    b = BFactory.create();;  // dependency #2, with BFactory
    b.doSomething();;
  }
}

// 3. type 0 IoC
public class A {
  public void doSomething(BIntf b); { // dependency #1, with BIntf
    b.doSomething();;
  }
}

// 4. type 2 IoC, setter injection
public class A {
  private BIntf _b;  // dependency #1, with BIntf 
  public void setB(BIntf b); {
    _b = b;
  }
  public void doSomething(); {
    _b.doSomething();;
  }
}

// 5. type 3 IoC, constructor injection
public class A {
  private BIntf _b;  // dependency #1, with BIntf 
  public A(BIntf b); {
    _b = b;
  }
  public void doSomething(); {
    _b.doSomething();;
  }
}