Question

What are wrapper classes and why are they useful for ArrayLists? In your answer, include examples of autoboxing and unboxing.

Your Discussion should be at least 250 words in length, but not more than 750 words. Once you’ve completed your initial post, be sure to respond to the posts of at least 3 of your classmates.

Answer 1

Wrapper classes:

• Wrapper classes are the part of Java programing language.
• Wrapper classes are basically used for to hold one primitive data ( primitive data types are those data types which is passed by value ) type value.
• Example: byte , short , int , long , float , double , boolean and char.

• Primitive type  Wrapper class
  boolean         Boolean
  byte            Byte
  char            Character
  float           Float
  int             Integer
  long            Long
  short           Short
  double          Double

• Wrapper classes object hold one value of their corresponding primitive type.
• Primitive value is stored in a field inside the object.
• This type of classes are used when we want store primitive data types in Java progaming structures that require objects like - Arraylists.
• Wrapper classes may be used with the help of Autoboxing and unboxing.
• Wrapper classes are used to provide the parse methods.
• It is also used for constants such as MAX_VALUE, MIN_VALUE.
• By the help of wrapper classes we can modify the arguments.

They are useful for ArrayLists because:

• ArrayLists cannot hold primitive data types such as int, double, char, and long hence for these reason we use wrapper classes.
• ArrayLists store only objects which is non primitive data types.
• ArrayLists element are accessed by same as array by index value.
• The size of a ArrayLists can grow or shrink as we need by adding and removing items after the ArrayLists has been created.

AutoBoxing: It is used for automatic conversion of primitive types to the object of their corresponding wrapper classes is known as autoboxing.

Example 1:- Let us we write:   Integer m = 6;

Java code :    Integer m = new Integer(6);

Example 2:- ArrayList runs = new ArrayList(); runs.add(9);

int r = runs.get(0);

Example 3:-

class Autoboxing
{
   public static void mySolution(Integer num){
        System.out.println(num);
   }
   public static void main(String[] args) {
        mySolution(10);
   }
}

Unboxing:

• It is reverse process of autoboxing.
• It is used to convert an object of a wrapper class to its corresponding primitive type is known as unboxing.

class Unboxing
{
   public static void mySolution(int num){
        System.out.println(num);
   }
   public static void main(String[] args) {
        
        Integer inum = new Integer(107);
        mySolution(inum);
    }
}