CSIS 110 โ Lecture 28
Reading -
Quiz โ Monday, March 28
Last time we looked at:
- Passing reference types to methods. Look at PassingReferences2.java, which
creates JFrames.
- Instance methods and the this keyword. Look at Point.java
All types are passed by value - it does not matter if the type of the formal parameter is a
primitive type or a reference type. This means that if we change the value of a formal
parameter, that change is not reflected back in the calling method.
Repeat KEY POINT:
If we change the value that is referenced by a reference type, that change is reflected
back in the caller. This is a subtle but important distinction!
Keyword this
Let's look at a class that defines a point on a two-dimensional grid - see Point.java. Look
at the constructor that takes two arguments
public Point( double xValue, double yValue )
I'd really like to give the formal parameters the names x and y instead of having to make
up new names for the same thing - points really have an x value and a y value. So, I'd like
to declare Point like this:
public Point( double x, double y )
What happens if I do it like this?
However, Java provides a way for us to do what I want - the keyword this. 'this' is a
reference to the current object. (Try to draw a picture). So, we can modify our code to use
this.
Class Variables
OK, we've seen instance methods, instance variables, and class methods. There is also
something called a class variable
Like a class method, a class variable is created using the keyword static.
[public/private] static <type> <identifier> = <initialization> ;
