Java Reference
In-Depth Information
1.
A new
Point
object is created and allocated in memory.
2.
The
Point
constructor is called on the newly created object, passing
7
and
2
as
the
initialX
and
initialY
parameter values.
3.
A
Point
reference variable named
p
is created and set to refer to the newly cre-
ated object.
Here is the complete code for the third version of our
Point
class, which now
contains a constructor:
1 // A Point object represents a pair of (x, y) coordinates.
2 // Third version: state and behavior with constructor.
3
4
public class
Point {
5
int
x;
6
int
y;
7
8 // constructs a new point with the given (x, y) location
9
public
Point(
int
initialX,
int
initialY) {
10 x = initialX;
11 y = initialY;
12 }
13
14 // returns the distance between this point and (0, 0)
15
public double
distanceFromOrigin() {
16
return
Math.sqrt(x * x + y * y);
17 }
18
19 // returns a String representation of this Point
20
public
String toString() {
21
return
"(" + x + ", " + y + ")";
22 }
23
24 // shifts this point's location by the given amount
25
public void
translate(
int
dx,
int
dy) {
26 x += dx;
27 y += dy;
28 }
29 }
Calling a constructor with parameters is similar to ordering a car from a factory:
“I'd like the yellow one with power windows and a CD player.” You might not need
to specify every detail about the car, such as the fact that it should have four wheels
and headlights, but you do specify some initial attributes that are important to you.
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