java create Creating Objects

java create Creating Objects

As you knowjava create,a class the for ; you an from a class. Each of the taken from the an and it to a :

Point originOne = new Point(23, 94);
Rectangle rectOne = new Rectangle(originOne, 100, 200);
Rectangle rectTwo = new Rectangle(50, 100);

The first line an of the Point classjava create, and the and third lines each an of the class.

Each of these has three parts ( in below):

: The code set in bold are all that a name with an type.: The new is a Java that the .: The new is by a call to a , which the new . a to Refer to an

, you that to a , you write:

type name;

This the that you will use name to refer to data whose type is type. With a , this also the of for the .

You can also a on its own line. For :

Point originOne;

If you like this, its value will be until an is and to it. a does not an . For that, you need to use the new , as in the next . You must an to you use it in your code. , you will get a error.

A in this state, which no , can be as (the name, ,plus a to ):

a Class

The new a class by for a new and a to that . The new also the .

Note: The ” a class” means the same thing as ” an .” When you anjava create, you are an “” of a class, “” a class.

The new a , : a call to a . The name of the the name of the class to .

The new a to the it . This is to a of the type, like:

Point originOne = new Point(23, 94);

The by the new does not have to be to a . It can also be used in an . For :

int height = new Rectangle().height;

This will be in the next .

an

Here's the code for the Point class:

public class Point {
    public int x = 0;
    public int y = 0;
    //constructor
    public Point(int a, int b) {
        x = a;
        y = b;
    }
}

This class a . You can a its uses the same name as the class and it has no type. The in the Point class takes two , as by the code (int a, int b). The 23 and 94 as for those :

Point originOne = new Point(23, 94);

The of this can be in the next :

Here's the code for the class,which four :

public class Rectangle {
    public int width = 0;
    public int height = 0;
    public Point origin;
    // four constructors
    public Rectangle() {
        origin = new Point(0, 0);
    }
    public Rectangle(Point p) {
        origin = p;
    }
    public Rectangle(int w, int h) {
        origin = new Point(0, 0);
        width = w;
        height = h;
    }
    public Rectangle(Point p, int w, int h) {
        origin = p;
        width = w;
        height = h;
    }
    // a method for moving the rectangle
    public void move(int x, int y) {
        origin.x = x;
        origin.y = y;
    }
    // a method for computing the area of the rectangle
    public int getArea() {
        return width * height;
    }
}

Each lets you for the 's,widthjava create Creating Objects,andjava create Creating Objects, using both and types. If a class has , they must have . The Java the based on the and the type of the . When the Java the code, it knows to call the in the class that a Point by two :

 
Rectangle rectOne = new Rectangle(originOne, 100, 200);

This calls one of 's that to . Also, the sets width to 100 and to 200. Now there are two to the same Point —an can have to it, as shown in the next :

The line of code calls the that two , which the for width and . If you the code the , you will see that it a new Point whose x and y are to 0:

Rectangle rectTwo = new Rectangle(50, 100);

The used in the doesn't take any , so it's a no- :

Rectangle rect = new Rectangle();

All have at least one . If a class does not any, the Java a no- , the . This calls the class 's no- , or the if the class has no other . If the has no ( does have one), the will the .