Autoboxing And Unboxing In Java

This slide describe what is autoboxing and unboxing in Java and give very good basic examples.

1. Autoboxing and Unboxing in JAVA Chathuranga Kasun Bamunusingha

2. Quick Review of Java Java is an oo language Can view everything as an object

3. Quick Review of Java Java is an oo language Can view everything as an object There are two type of variables in java Primitive (int,char,bool…..) Object

4. Quick Review of Java Java is an oo language Can view everything as an object There are two type of variables in java Primitive (int,char,bool…..) Object Simple data types can be converted into objects Using “Wrapper” classes

5. Quick Review of Java Wrapper classes wrap primitive data types and give it an object appearance Int -> Integer Char -> Character Use of wrapper classes To convert simple data types into objects To convert strings into relavent data types Ex Integer.parseInt(“100”);

6. Quick Review of Java Wrapper classes wrap primitive data types and give it an object appearance Int -> Integer Char -> Character

7. Quick Review of Java Wrapper class provides methods to wrap and unwrap objects Ex: Wrap -> Integer k=new Integer(100); Unwrap -> int a=k.intValue(); It simply like a “Chocolate”! Manufacture wrap the chocolate with some paper(wrapper) User takes it and remove the paper(wrapper) and eat

8. Autoboxing and Unboxing Autoboxing Wrap a primitive data type into its object type

9. Autoboxing and Unboxing Autoboxing Wrap a primitive data type into its object type Unboxing Unwrap(get the primitive value) from its relevant object

10. Autoboxing and Unboxing Autoboxing Wrap a primitive data type into its object type Unboxing Unwrap(get the primitive value) from its relevant object I made some mistakes!!!!!! How the “Auto” parts comes to the picture! You just wait ;)

11. Back To Java History I’m going to write some code in java 4.0!

12. Back To Java History Now I want to add “3” into listOfNumbers arraylist listOfNumbers.add(3);

13. Back To Java History Now I want to add “3” into listOfNumbers arraylist listOfNumbers.add(3); This gives me an ERROR!!!

14. Back To Java History Now I want to add “3” into listOfNumbers arraylist listOfNumbers.add(3); This gives me an ERROR!!! There is no add(int) method , only add(object) method

15. Back To Java History Now I want to add “3” into listOfNumbers arraylist listOfNumbers.add(3); This gives me an ERROR!!! There is no add(int) method , only add(object) method listOfNumbers.add(new Integer(3));

16. Back To Java History If I need to take that number “3” back, then

17. Back To Java History If I need to take that number “3” back, then It comes out as type of Object Integer one = (Integer) listOfNumbers.get(0);

18. Back To Java History If I need to take that number “3” back, then It comes out as type of Object Integer one = (Integer) listOfNumbers.get(0); Finally you can get the primitive out of the Integer int intOne = one.intValue();

19. What is the problem mate! In every time you (the programmer) has to do the wrapping(boxing) and unwrapping (unboxing) manually

20. What is the problem mate! In every time you (the programmer) has to do the wrapping(boxing) and unwrapping (unboxing) manually It makes coding life bit difficult It can be introduce bugs in the program

21. What is the problem mate! In every time you (the programmer) has to do the wrapping(boxing) and unwrapping (unboxing) manually It makes coding life bit difficult It can be introduce bugs in the program How to solve this ?

22. What is the problem mate! In every time you (the programmer) has to do the wrapping(boxing) and unwrapping (unboxing) manually It makes coding life bit difficult It can be introduce bugs in the program How to solve this ? If compiler do this automatically for the programmer then life will be easy! That exactly java 5 has done! We called it “Autoboxing and unboxing”

23. Back To Java 5 Let’s do the previous example in java 5

24. Back To Java 5 Let’s do the previous example in java 5 Make an ArrayList of type Integer ArrayList<Integer> listOfNumbers = new ArrayList<Integer>();

25. Back To Java 5 Let’s do the previous example in java 5 Make an ArrayList of type Integer ArrayList<Integer> listOfNumbers = new ArrayList<Integer>(); Just add it!

26. Back To Java 5 Let’s do the previous example in java 5 Make an ArrayList of type Integer ArrayList<Integer> listOfNumbers = new ArrayList<Integer>(); Just add it! listOfNumbers.add(3); Here converting int 3 into Integer object has been done by the compiler itself (Autoboxing) Now “Auto” word comes into the picture!

27. Back To Java 5 If I need to get the int value from Integer object ,

28. Back To Java 5 If I need to get the int value from Integer object , int num = listOfNumbers.get(0); Here getting int value from Integer object is done by the compiler itself

29. Back To Java 5 If I need to get the int value from Integer object , int num = listOfNumbers.get(0); Here getting int value from Integer object is done by the compiler itself That is intValue() method is called by the compiler We called it “unboxing”!

30. Lets Have Fun With Autoboxing and Unboxing! As method arguments

31. Lets Have Fun With Autoboxing and Unboxing! As method arguments takeNumber method takes an Integer object as input parameter. But we can use int also!

32. Lets Have Fun With Autoboxing and Unboxing! Return values

33. Lets Have Fun With Autoboxing and Unboxing! Return values giveNumber method return int. but it can be used int or Integer type!

34. Lets Have Fun With Autoboxing and Unboxing! Boolean expressions

35. Lets Have Fun With Autoboxing and Unboxing! Boolean expressions

36. Lets Have Fun With Autoboxing and Unboxing! Operations on numbers Compiler do the trick!

37. Lets Have Fun With Autoboxing and Unboxing! Assignments

38. Lets Have Fun With Autoboxing and Unboxing! Assignments

39. End OF The Journey That’s all about autoboxing and unboxing!

40. End OF The Journey That’s all about autoboxing and unboxing! Any questions ???

41. End OF The Journey That’s all about autoboxing and unboxing! Any questions ??? Thank you!