Explain wrapper classes in Java?

Java provides certain classes called wrapper classes in the java.lang package. The objects of these classes wraps primitive datatypes within them. Following is the list of primitive datatypes and their respective classes −

Following Java example accepts various primitive variables from the user and creates their respective wrapper classes.

Example

import java.util.Scanner;
public class WrapperClassesExample {
   public static void main(String args[]){
      Scanner sc = new Scanner(System.in);
      System.out.println("Enter an integer value: ");
      int i = sc.nextInt();
      //Wrapper class of an integer
      Integer obj1 = new Integer(i);
      System.out.println("Enter a long value: ");
      long l = sc.nextLong();
      //Wrapper class of a long
      Long obj2 = new Long(l);
      System.out.println("Enter a float value: ");
      float f = sc.nextFloat();
      //Wrapper class of a float
      Float obj3 = new Float(f);
      System.out.println("Enter a double value: ");
      double d = sc.nextDouble();
      //Wrapper class of a double
      Double obj4 = new Double(d);
      System.out.println("Enter a boolean value: ");
      boolean bool = sc.nextBoolean();
      //Wrapper class of a boolean
      Boolean obj5 = new Boolean(bool);
      System.out.println("Enter a char value: ");
      char ch = sc.next().toCharArray()[0];
      //Wrapper class of a boolean
      Character obj6 = new Character(ch);
      System.out.println("Enter a byte value: ");
      byte by = sc.nextByte();
      //Wrapper class of a boolean
      Byte obj7 = new Byte(by);
      System.out.println("Enter a short value: ");
      short sh = sc.nextShort();
      //Wrapper class of a boolean
      Short obj8 = new Short(sh);
   }
}

Output

Enter an integer value:
254
Enter a long value:
4444445455454
Enter a float value:
12.324
Enter a double value:
1236.22325
Enter a boolean value:
true
Enter a char value:
c
Enter a byte value:
125
Enter a short value:
14233

Following are some important points on wrapper classes.

• At the time of instantiation these classes accept a primitive datatype directly, or in the form of String.

Int i = 20;
Integer obj = new Integer(i);
Or,
Integer obj = new Integer("20");

• Wrapper classes provides methods to, convert primitive datatypes within them to String objects and, to compare them with other objects etc.

Example

import java.util.Scanner;
public class WrapperExample {
   public static void main(String args[]){
      Scanner sc = new Scanner(System.in);
      System.out.println("Enter an integer value: ");
      int i = sc.nextInt();
      //Wrapper class of an integer
      Integer obj = new Integer(i);
      //Converting Integer object to String
      String str = obj.toString();
      System.out.println(str);
   }
}

Output

Enter an integer value:
124
124

• Using wrapper classes, you can also add primitive datatypes to various Collection objects such as ArrayList, HashMap etc. You can also pass primitive values over network using wrapper classes.

Example

import java.util.Scanner;
public class WrapperExample {
   public static void main(String args[]){
      Scanner sc = new Scanner(System.in);
      System.out.println("Enter an integer value: ");
      int i = sc.nextInt();
      //Wrapper class of an integer
      Integer obj = new Integer(i);
      //Converting Integer object to String
      String str = obj.toString();
      System.out.println(str);
      //Comparing with other object
      int result = obj.compareTo(new Integer("124"));
      if(result==0) {
         System.out.println("Both are equal");
      }else{
         System.out.println("Both are not equal");
      }
   }
}

Output

Enter an integer value:
1211
1211
Both are not equal