Detailed explanation of the global variables and passing values ​​in Android Application

/**
 * Rewrite Application, mainly rewrite the onCreate method inside, that is, when it is created,
 * We asked it to initialize some values. I saw an example in javaeye some time ago, similar to this.
 * I made some improvements.  I heard that foreign developers are used to initializing some global variables with this, as if in Activity
 * When initializing the global variables in some classes, you will encounter some null pointer exceptions. Of course, I have never encountered them.
 * If initialized with this method, then those possible errors can be avoided.
 *
 * When you start Application, it will create a PID, which is the process ID, and all activities will run on this process.
 * So when we initialize global variables when the Application is created, can all activities get these
 * Global variables, furthermore, we have changed the values ​​of these global variables in a certain activity, so in other activities
 * Does the value change? Is this considered a passing value?
 * OK, then let's test the following example.  .  .
 * @author
 *
 */
public class MyApplication extends Application {
private String name;
@Override
public void onCreate() {
();
setName(NAME); //Initialize global variables}
public String getName() {
return name;
}
public void setName(String name) {
 = name;
}
private static final String NAME = "MyApplication";
}

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:andro
package=""
android:versionCode="1"
android:versionName="1.0">
<application android:icon="@drawable/icon" android:label="@string/app_name"
android:name=".MyApplication"> That's it，Use the default we have always used beforeApplicationSet it for him to do it ourselvesMyApplication
<activity android:name=".MyFirstActivity"
android:label="@string/app_name">
<intent-filter>
<action android:name="" />
<category android:name="" />
</intent-filter>
</activity>
<activity android:name=".MySecondActivity"></activity>
</application>
<uses-sdk android:minSdkVersion="8" />
</manifest>

public class MyFirstActivity extends Activity {
private MyApplication app;
@Override
public void onCreate(Bundle savedInstanceState) {
(savedInstanceState);
setContentView();
app = (MyApplication) getApplication(); //Get our application MyApplication("MyFirstActivityOriginal", ()); //Take out the global variables we put into the process to see if they are the values ​​we have set before("is cool"); //OK, now we've started to modify("MyFirstActivityChanged", ()); //Look at it again, has this value changed?Intent intent = new Intent(); //More importantly, we can see whether we get the initialized value in other activities or modified(this, );
startActivity(intent);
}
}

public class MySecondActivity extends Activity {
private MyApplication app;
@Override
protected void onCreate(Bundle savedInstanceState) {
(savedInstanceState);
setContentView();
app = (MyApplication) getApplication(); //Get the application("MySecondActivity", ()); //Get global value}
}

MyFirstActivityOriginal MyApplication 
MyFirstActivityChanged is cool
MySecondActivity is cool