This document summarizes a lecture on arrays as parameters in Java. It discusses how objects and arrays are passed by reference in methods, so any changes made to the parameter inside the method will affect the original variable. It provides examples of passing both individual array elements and entire arrays as parameters. The document is for a CSE110 Principles of Programming with Java class taught by Javier Gonzalez-Sanchez in the summer of 2017, and references Chapter 6 as further reading.

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

2. Objects as Parameters

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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

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Object as Parameters

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Objects as Parameters

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Objects as Parameters

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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.

8. Arrays as Parameters

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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

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Example

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Arrays of Objects

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Arrays of Objects

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Reference
Chapter 6

14. CSE110 - Principles of Programming
Javier Gonzalez-Sanchez
javiergs@asu.edu
Summer 2017
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.