CSE110 Lecture 25

Principles of Programming with Java
Arrays as Parameters
(202007)

Transcript

1. CSE110
   Principles of Programming
   with Java
   Lecture 25:
   References as Parameters
   Javier Gonzalez-Sanchez
   javiergs@asu.edu
   javiergs.engineering.asu.edu | javiergs.com
   Office Hours: By appointment
   

   View Slide

2. Objects as Parameters
   

   View Slide

3. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 3
   Objects as Parameters
   • Parameters in a Java method are passed by value
   • This means that a copy of the actual parameter
   (the value passed in) is stored into the formal
   parameter (in the method header)
   • Passing parameters is therefore similar to an
   assignment statement
   • When an object is passed as a parameter to a
   method, the actual parameter and the formal
   parameter become aliases of each other
   

   View Slide

4. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 4
   Object as Parameters
   

   View Slide

5. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 5
   Objects as Parameters
   • Since a1 is a primitive data, any change that was made
   to f1 in the method changeValues does not affects a1
   • The object a2 was assigned to the value “222” and
   when a2 was passed to changeValues method, a2 and
   f2 became aliases so the change made to f2 will be
   seen in a2 in the main method.
   • The object a3 was assigned to the value “333” and
   when a3 was passed to changeValues method, a3 and
   f3 became aliases.
   However when f3 was re-instantiated with the reserved
   word new, f3 is given a different address from the one a3
   has, thus any change made to f3 after that point will not
   affect a3 in the main method.
   

   View Slide

6. Arrays as Parameters
   

   View Slide

7. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 7
   Arrays as Parameters
   • An entire array can be passed as a parameter to a
   method
   • Object and arrays are passed as a reference,
   making the formal and actual parameters aliases of
   each other
   • Therefore, changing an array element within the
   method changes the original
   • An individual array element can be passed to a
   method as well, in which case the type of the
   formal parameter is the same as the element type
   

   View Slide

8. Javier Gonzalez-Sanchez | CSE110 | Summer 2017 | 8
   Example
   

   View Slide

9. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 9
   Arrays of Objects
   

   View Slide

10. Javier Gonzalez-Sanchez | CSE110 | Summer 2020 | 10
    Arrays of Objects
    

    View Slide

11. Javier Gonzalez-Sanchez | CSE110 | Summer 2017 | 11
    Reference
    Chapter 6
    

    View Slide

12. CSE110 - Principles of Programming
    Javier Gonzalez-Sanchez
    javiergs@asu.edu
    Summer 2020
    Disclaimer. These slides can only be used as study material for the class CSE110 at ASU. They cannot be distributed or used for another purpose.
    

    View Slide