Class Turtle

  • public class Turtle
extends Object
    This class represents a "turtle" that can be asked to change directions and move around the screen. It's similar to the concept of the Logo turtle, though with only four possible headings. The version below has been modified for use in a 161 lab: It has a copy constructor that the original didn't, and there are getter methods for providing information about the turtle's state.
    Version:
    2.0
    Author:
    Brad Richards

    • Constructor Summary

      Constructors 
      Constructor Description
      Turtle()
      This constructor sets up our "turtle" and leaves it facing north.
      Turtle​(int initialDistance)
      The second constructor allows the user to specify how far our turtle should move each time forward() is called: It takes a parameter containing this extra information, and uses an assignment statement to store a copy of that value in our distance field.
      Turtle​(Turtle other)
      This copy constructor takes another Turtle object for inspiration, and sets "us" up to look just like them.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      boolean equals​(Turtle other)
      Compares our state with that of another turtle.
      void faceEast()
      Change the turtle's state so that we're heading east.
      void faceNorth()
      Change the turtle's state such that we'll head "north" (up the screen) the next time forward() is called.
      void faceSouth()
      Change the turtle's state so that we're heading south.
      void faceWest()
      Change the turtle's state so that we're heading west.
      void forward()
      Move in the direction we're heading, by the number of pixels stored in the distance field.
      Circle getCircle()
      A "getter" method that returns a reference to our Circle object.
      int getXDirection()
      A "getter" method for providing the turtle's xDirection.
      int getYDirection()
      A "getter" method for providing the turtle's yDirection.
      void setDistance​(int newDistance)
      The setDistance method can be used to change how far the turtle moves each time forward() is called.

    • Constructor Detail

      • Turtle

        public Turtle()
        This constructor sets up our "turtle" and leaves it facing north. It arbitrarily decides that we should move in 20-pixel increments.

      • Turtle

        public Turtle​(int initialDistance)
        The second constructor allows the user to specify how far our turtle should move each time forward() is called: It takes a parameter containing this extra information, and uses an assignment statement to store a copy of that value in our distance field. Notice the sneaky trick it's using to avoid duplicating the code above: Java lets you call one constructor from another by using the name "this" in place of a method name. The first line below is calling the default (no-input) constructor above to do most of the setup, and then just changing the distance.
        Parameters:
        initialDistance - The value to use for distance.

      • Turtle

        public Turtle​(Turtle other)
        This copy constructor takes another Turtle object for inspiration, and sets "us" up to look just like them. We have to take special care to be sure that we don't share a Circle object with them -- we want our Circle to be independent from theirs, but to take on the same *values* as their Circle.
        Parameters:
        other - A reference to another Turtle we want to copy.

    • Method Detail

      • equals

        public boolean equals​(Turtle other)
        Compares our state with that of another turtle. We consider the two to be equal if our X and Y directions both match, our distance is the same as theirs, and our two Circles are at the same location.
        Returns:
        True if our state matches that of the other turtle, false otherwise.

      • getXDirection

        public int getXDirection()
        A "getter" method for providing the turtle's xDirection.
        Returns:
        Our xDirection value.

      • getYDirection

        public int getYDirection()
        A "getter" method for providing the turtle's yDirection.
        Returns:
        Our yDirection value.

      • getCircle

        public Circle getCircle()
        A "getter" method that returns a reference to our Circle object.
        Returns:
        A reference to our Circle.

      • forward

        public void forward()
        Move in the direction we're heading, by the number of pixels stored in the distance field. The direction is represented by a pair of fields, each of which is expected to be either 0, 1, or -1. We can figure out how far to move in each dimension by multiplying the direction by distance.

      • setDistance

        public void setDistance​(int newDistance)
        The setDistance method can be used to change how far the turtle moves each time forward() is called. It takes this information as a parameter, and stores a copy of the value into our distance field using an assignment statement.
        Parameters:
        newDistance - The new value to use for distance.

      • faceNorth

        public void faceNorth()
        Change the turtle's state such that we'll head "north" (up the screen) the next time forward() is called. There's no movement along the X axis involved in moving north, so xDirection is set to 0. The yDirection field is set to -1 since movement up the screen is in the negative direction.

      • faceSouth

        public void faceSouth()
        Change the turtle's state so that we're heading south.

      • faceWest

        public void faceWest()
        Change the turtle's state so that we're heading west.

      • faceEast

        public void faceEast()
        Change the turtle's state so that we're heading east.