CS 100: Lecture L14

March 11

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// First example with arrays.
import java.awt.*;

public class ShowMedians extends Frame
{
  
	public void paint(Graphics g)
	{
	   g.setColor(Color.black);
	   g.fillRect(0,0,1000,1000);
	   // Create arrays for the vertex coordinates and the midpoint coordinates.
	   int[] h = new int[3];
	   int[] v = new int[3];
	   int[] hMid = new int[3];
	   int[] vMid = new int[3];
	   
	   // Initialize the vertex coordinates.
	   h[0] = 100; h[1] = 700; h[2] = 300;
	   v[0] = 500; v[1] = 500; v[2] = 100;
	   
	   // Draw the sides
	   g.setColor(Color.blue);
	   g.drawLine(h[0],v[0],h[1],v[1]);
	   g.drawLine(h[1],v[1],h[2],v[2]);
	   g.drawLine(h[2],v[2],h[0],v[0]);
	   
	   // Compute the midpoint coordinates
	   
	   hMid[0] = (h[0]+h[1])/2 ; vMid[0] = (v[0]+v[1])/2;
	   hMid[1] = (h[1]+h[2])/2 ; vMid[1] = (v[1]+v[2])/2;
	   hMid[2] = (h[2]+h[0])/2 ; vMid[2] = (v[2]+v[0])/2;
	   
	   // Connect each vertex with the opposite midpoint
	   g.setColor(Color.red);
	   g.drawLine(h[0],v[0],hMid[1],vMid[1]);
	   g.drawLine(h[1],v[1],hMid[2],vMid[2]);
	   g.drawLine(h[2],v[2],hMid[0],vMid[0]);
	   
	   // Display the Centroid.
	   int hBar = (h[0]+h[1]+h[2])/3;
	   int vBar = (v[0]+v[1]+v[2])/3;
	   g.fillOval(hBar-5,vBar-5,10,10);
	   
	
	}
	
}

public class L14A
{
	public static void main(String args[])
	{
		ShowMedians d = new ShowMedians();
		d.resize(1000,600);                     
		d.move(0,75);
		d.setTitle("The Medians of a Triangle Intersect at the Centroid");                 
		d.show();
		d.toFront();
	}
}

// Arrays and loops.
import java.awt.*;

public class ShowCentroid extends Frame
{
    final static int nMax = 200;
    final static int m = 50;
    final static int L = 800;
    final static int W = 500;
    
    
	public void paint(Graphics g)
	{
	   g.setColor(Color.black);
	   g.fillRect(0,0,1000,1000);
	   // Generate the random points
	   int[] h = new int[nMax];
	   int[] v = new int[nMax];
	   for(int i=0;i&ltnMax;i++)
	   {
	      h[i] = (int) (m + L*Math.random());
	      v[i] = (int) (m + W*Math.random());
	   }
	   
	   // Compute the centroid (hBar,vBar) where hBar (vBar) is the
	   // average of the h-values (v-values).
	   int hSum = 0; 
	   int vSum = 0;
	   for(int j=0;j&ltnMax;j++)
	   {
	      hSum = hSum + h[j];
	      vSum = vSum + v[j];
	   }
	   int hBar = hSum/nMax;
	   int vBar = vSum/nMax;
	   
	   // Display the line segments that connect the points and the centroid.
	   for(int k=0;k&ltnMax;k++)
	   {
	      g.setColor(Color.pink);
	      g.drawLine(hBar,vBar,h[k],v[k]);
	   }
	   
	   // Highlight points and  the centroid.
	   for(int k=0;k&ltnMax;k++)
	   {
	      g.setColor(Color.red);
	      g.fillOval(h[k]-4,v[k]-4,8,8);
	   }
	   g.setColor(Color.blue);
	   g.fillOval(hBar-5,vBar-5,10,10);
	
	   // Identify and highlight the point furthest from the centroid.
	   double d;                // distance from centroid to the ith point.
	   double dMax = 0;         // Maximum distance from the centroid.
	   int iMax=0;              // Index of the point furthest from the centroid.
	   for(int i=0;i&ltnMax;i++)
	   {
	      // See in (h[i],v[i]) is the new "furthest point" from the centroid.
	      d = Math.sqrt(Math.pow(hBar-h[i],2)+Math.pow(vBar-v[i],2));
	      if(d>dMax)
	      {
	         dMax = d;
	         iMax = i;   
	      }
	   }
	   g.setColor(Color.green);
	   g.fillOval(h[iMax]-5,v[iMax]-5,10,10);
	}
	
}

public class L14B
{
	public static void main(String args[])
	{
		ShowCentroid d = new ShowCentroid();
		d.resize(1000,600);                     
		d.move(0,75);
		d.setTitle("Centroid");                
		d.show();
		d.toFront();
	}
}