Question

I have learned that in a class you can declare variables and methods. They can both be declared as static if that is prefered.

Now I have encountered a program example I do not really understand. After some variable declaration in the class there is a field declared as static and inside there is program code.

When is this code executed? My guess is that the code is executed like following when a new object is created:

1. Memory allocation for the instance variables.
2. Execution of the contructors connected to the instance variables.
3. Exection of the static field
4. Execution of the constructor (if “= new Constructor() is used when the object is created)

If I execute

MyCars myCars = new MyCars();

the following will happen in this order?

public class MyCars
{
    private Car volvo = new Car()
 //              (1)       (2)
    static
    {
        volvo.setNumberOfWheels = 4;
 //                  (3)
    }

    public MyCars()
    {
         volvo.setBrand = "Volvo";
         volvo.setModel = "XC70";
                 (4)
    }

Here is the original code:

public class SettingsSetter extends ListActivity
{
    private static Map<Integer,String> menuActivities=new HashMap<Integer,String>();
    private static List<BooleanSetting> settings=new ArrayList<BooleanSetting>();

    static 
    {
        menuActivities.put(R.id.app,
            Settings.ACTION_APPLICATION_SETTINGS);
        menuActivities.put(R.id.security, Settings.ACTION_SECURITY_SETTINGS);
        menuActivities.put(R.id.wireless,
            Settings.ACTION_WIRELESS_SETTINGS);
        menuActivities.put(R.id.all,
            Settings.ACTION_SETTINGS);

        settings.add(new BooleanSetting(Settings.System.INSTALL_NON_MARKET_APPS,
            "Allow non-Market app installs", true));
        settings.add(new BooleanSetting(Settings.System.HAPTIC_FEEDBACK_ENABLED,
            "Use haptic feedback", false));
        settings.add(new BooleanSetting(Settings.System.ACCELEROMETER_ROTATION,
            "Rotate based on accelerometer", false));
    }

Answer 1

Static initialisers are executed when the class is loaded, so before any instances are created. Your first code is in error, since volvo is an instance (non-static) variable, and the static block cannot access it. Revisiting your example:

public class MyCars
{
    private static Car audi = new Car()
 //                     (2)
    private Car volvo = new Car()
 //              (5)       (6)
    static
    {
        audi.setNumberOfWheels = 4;
 //                  (3)
    }
    public MyCars()
    {
         volvo.setBrand = "Volvo";
         volvo.setModel = "XC70";
 //              (7)
    }
}

MyCars myCars = new MyCars();
// (1)                (4)