A Quick Tour - The Java Programming Language - page 25

compatible with the return type defined for the method. In the example
we use the sqrt method of the Math library class to calculate the square
root of the sum of the squares of the differences between the two x and
y coordinates.
Based on the lowerLeft and upperRight objects created previously, you
could invoke distance this way:
double d = lowerLeft.distance(upperRight);
Here upperRight is passed as an argument to distance , which sees it as
the parameter that . After this statement executes, the variable d con-
tains the Euclidean distance between lowerLeft and upperRight .
1.8.2. The this Reference
Occasionally, the receiving object needs to know its own reference. For
example, the receiving object might want to add itself to a list of objects
somewhere. An implicit reference named this is available to methods,
and this is a reference to the current (receiving) object. The following
definition of clear is equivalent to the one just presented:
public void clear() {
this.x = 0.0;
this.y = 0.0;
}
You usually use this as an argument to other methods that need an ob-
ject reference. The this reference can also be used to explicitly name the
members of the current object. Here's another method of Point named
move , which sets the x and y fields to specified values:
public void move(double x, double y) {
this.x = x;