Java

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Introduction ​

What are Wrapper Classes? ​

Wrapper classes are part of Java's standard library java.lang and these convert primitive datatypes in an object. To be more specific, a wrapper class wraps a value of primitive type in an object. In addition, the wrapper classes also provide tools , methods and constants(the smallest and largest int value, etc.)

All wrapper classes are part of java.lang package.

Available Wrapper Classes : ​

  • Boolean - java.lang.Boolean
  • Byte - java.lang.Boolean
  • Character - java.lang.Character
  • Double - java.lang.Double
  • Float - java.lang.Float
  • Integer - java.lang.Integer
  • Long Short - java.lang.Short

Void class

There is also Void class but it's object cannot be created.

Reasons for having wrapper classes : ​

  • Java is an object oriented language where everything is used as objects. The wrapper classes enable a primitive value to be used as objects. As objects they can be used with all types of classes and their methods.

  • Wrapper classes provide many ready-to-use utility methods such as converting a string having primitive type value to equivalent primitive form e.g., "10" can be converted to integer 10 using a wrapper class method; and many other functions.

  • Primitive data types are passed by value, but objects are passed by reference. Wrapper classes facilitate passing primitives by reference, as an argument to a method, if so required.

  • There are some other reasons that make wrapper classes useful in advanced Java (such as with data structures and some frameworks etc.)

The wrapper classes are final, i.e. once assigned to a value, the value cannot of the wrapper class cannot be changed. Java does this to ensure uniform capabilities accross all instances.

Autoboxing

You can assign a primitive value to its wrapper class object and Java will automatically wrap around or box around sn object on the primitive value, this is called autoboxing.

Unboxing

You can assign a wrapper class object's value to its primitive type and Java will automatically unwrap the object around the primitive value, this is called unboxing.