[Chapter 2] 2.2 Point

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| Chapter 2 Simple Graphics |

## 2.2 Point

The `Point` class encapsulates x and y coordinates within a single object. It is probably one of the most underused classes within Java. Although there are numerous places within AWT where you would expect to see a `Point`, its appearances are surprisingly rare. Java 1.1 is starting to use `Point` more heavily. The `Point` class is most often used when a method needs to return a pair of coordinates; it lets the method return both x and y as a single object. Unfortunately, `Point` usually is not used when a method requires x and y coordinates as arguments; for example, you would expect the `Graphics` class to have a version of `translate()` that takes a point as an argument, but there isn't one.

The `Point` class does not represent a point on the screen. It is not a visual object; there is no `drawPoint()` method.

### Point Methods

Variables

The two public variables of `Point` represent a pair of coordinates. They are accessible directly or use the `getLocation()` method. There is no predefined origin for the coordinate space.

public int x

  The coordinate that represents the horizontal position.

public int y

  The coordinate that represents the vertical position.

Constructors

public Point ()

  The first constructor creates an instance of `Point` with an initial x value of 0 and an initial y value of 0.

public Point (int x, int y)

  The next constructor creates an instance of `Point` with an initial x value of `x` and an initial y value of `y`.

public Point (Point p)

  The last constructor creates an instance of `Point` from another point, the x value of `p.x` and an initial y value of `p.y`.

Locations

public Point getLocation ()

  The `getLocation()` method retrieves the current location of this point as a new `Point`.

public void setLocation (int x, int y)
public void move (int x, int y)

  The `setLocation()` method changes the point's location to (`x`, `y`).

  `move()` is the Java 1.0 name for this method.

public void setLocation (Point p)

  This `setLocation()` method changes the point's location to (`p.x`, `p.y`).

public void translate (int x, int y)

  The `translate()` method moves the point's location by adding the parameters (`x`, `y`) to the corresponding fields of the `Point`. If the original `Point p` is (3, 4) and you call `p.translate(4, -5)`, the new value of `p` is (7, -1).

Miscellaneous methods

public int hashCode ()

  The `hashCode()` method returns a hash code for the point. The system calls this method when a `Point` is used as the key for a hash table.

public boolean equals (Object object)

  The `equals()` method overrides the `Object.equals()` method to define equality for points. Two `Point` objects are equal if their x and y values are equal.

public String toString ()

  The `toString()` method of `Point` displays the current values of the x and y variables. For example:

      java.awt.Point[x=100,y=200]

Graphics |  | Dimension