java 监听器实现原理

public class MyActivity extends Activity implements InternetManager.Listener {

private TextView mText;
private InternetManager mInetMgr;

/* called just like onCreate at some point in time */
public void onStateChange(boolean state) {
if (state) {
mText.setText("on");
} else {
mText.setText("off");
}
}

public void onCreate() {
mInetMgr = new InternetManager();
mInetMgr.registerListener(this);
mInetMgr.doYourWork();
}
}

public class InternetManager {
// all the listener stuff below
public interface Listener {
public void onStateChange(boolean state);
}

private Listener mListener = null;
public void registerListener (Listener listener) {
mListener = listener;
}

// -----------------------------
// the part that this class does

private boolean isInternetOn = false;
public void doYourWork() {
// do things here
// at some point
isInternetOn = true;
// now notify if someone is interested.
if (mListener != null)
mListener.onStateChange(isInternetOn);
}
}