Release Memory, Valid URL, Valid Email, Valid Phone

1) How we release a memory in android ?
Answer :- Suppose if we use in our activity
                     Button btnYes;
                     LinearLayout llMain;
                     Gallery gallery
                     ImageButton btnSearch
                     ImageView backImageView;
 

@Override
 protected void onPause() {
       releaseViewMemory(btnYes);
       releaseViewMemory(llMain);
       releaseViewMemory(gallery);
                                   releaseViewMemory(btnSearch);         
                                   releaseImageViewMemory(backImageView);
                                   super.onPause();
                             }

public static void releaseViewMemory(View view) {
    if (view != null) {
        Drawable draw = view.getBackground();
        if (draw != null) {
           draw.setCallback(null);
           draw = null;
        }
   }
}

public static void releaseImageViewMemory(ImageView imgView) {
     if (imgView != null) {
         Drawable draw = imgView.getBackground();
         if (draw != null) {
            draw.setCallback(null);
            draw = null;
         }
         draw = imgView.getDrawable();
         if (draw != null) {
            draw.setCallback(null);
            draw = null;
         }
     }
}

2) Write a method for valid url.
Answer :- 

public static boolean isValidURL(String url) {

    boolean isValid = false;
    String expression = "^(http|https|ftp)\\://[a-zA-Z0-9\\-\\.]+\\.[a-zA-Z]{2,3}(:[a-zA-Z0-9]*)?/?([a-zA-Z0-9\\-\\._\\?\\,\\'/\\\\+&%\\$#\\=~])*$";
   CharSequence inputStr = url;
   Pattern pattern = Pattern.compile(expression, Pattern.CASE_INSENSITIVE);
   Matcher matcher = pattern.matcher(inputStr);
   if (matcher.matches()) {
      isValid = true;
   }
   return isValid;
}

3) Write a method for valid email.
Answer :- 

public static boolean isValidEmail(String email) {
    boolean isValid = false;
    String expression = "^[\\w\\.-]+@([\\w\\-]+\\.)+[A-Z]{2,4}quot;;
    CharSequence inputStr = email;
    Pattern pattern = Pattern.compile(expression, Pattern.CASE_INSENSITIVE);
    Matcher matcher = pattern.matcher(inputStr);
    if (matcher.matches()) {
        isValid = true;
    }
    return isValid;
}


3) Write a method for valid phone.
Answer :- 
public static boolean isValidphone(String phone) {
    boolean isValid = false;
    String expression = "^[+][0-9]{10,13}$";
    CharSequence inputstr = phone;
    if (phone.length() == 0)
        return false;
    Pattern pattern = Pattern.compile(expression, Pattern.CASE_INSENSITIVE);
    Matcher matcher = pattern.matcher(inputstr);
    if (matcher.matches()) {
        if (phone.length() == 10)
            isValid = true;
        }
        return isValid;
   }

Core Java Questions Part-2

1) What is Collection ?

Answer : Collection — the root of the collection hierarchy. A collection represents a group of objects known as its elements. The Java platform doesn't provide any direct implementations of this interface but provides implementations of more specific subinterfaces, such as Set and List. 

1. 
   

è Set — A Set is a Collection that cannot contain duplicate elements. It models the mathematical set abstraction. The Set interface contains only methods inherited from Collection and adds the restriction that duplicate elements are prohibited.

Ø  SortedSet — a Set that maintains its elements in ascending order.

è List — A List is an ordered Collection (sometimes called a sequence). Lists may contain duplicate elements.

Ø  ArrayList - Resizable-array implementation of the List interface. Implements all optional list operations, and permits all elements, including null.

Ø  LinkedList

Ø  Vector - The Vector class implements a growable array of objects. Like an array, it contains components that can be accessed using an integer index.

è Queue — A collection used to hold multiple elements prior to processing. Besides basic Collection operations, a Queue provides additional insertion, extraction, and inspection operations.

è Map — An object that maps keys to values. A Map cannot contain duplicate keys; each key can map to at most one value.

o   SortedMap — A Map that maintains its mappings in ascending key order.

2) What is the difference between List, Set and Map? 

Answer : A Set is a collection that has no duplicate elements. A List is a collection that has an order associated with its elements. A map is a way of storing key/value pairs. The way of storing a Map is similar to two-column table.

3) What is the difference between Vector and ArrayList ?
Answer : Vector is synchronized, ArrayList is not. Vector is having a constructor to specify the incremental capacity. But ArrayList don't have. By default Vector grows by 100% but ArrayList grows by 50% only.

4) What is the difference between Hashtable and HashMap ?
Answer : Hashtable is synchronized . but HashMap is not synchronized. Hashtable does not allow null values , but HashMap allows null values.

5) What is the difference between array and ArrayList ?
Answer : Array is collection of same data type. Array size is fixed, It cannot be expanded. But ArrayList is a growable collection of objects. ArrayList is a part of Collections Framework and can work with only objects.

6) What is any an anonymous class?
Answer : An anonymous class is a local class with no name.

7) What is the difference between synchronized block and synchronized method ?

Answer : Synchronized blocks place locks for the specified block where as synchronized methods place locks for the entire method.