Chapter 28 Exercise 24, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

28.24 (Remove a circle) Modify Listing 28.10, ConnectedCircles.java, to enable the user to remove a circle when the mouse is clicked inside the circle.

import java.util.List;
import java.util.ArrayList;

import javax.swing.*;

import java.awt.*;
import java.awt.event.*;

public class Exercise24 extends JApplet {
 private static final long serialVersionUID = 1L;
 // Circles are stored in a list
 private List<Circle> circles = new ArrayList<Circle>();
 private int movedCircle;
 private boolean isMoving = false;
 private CirclePanel circlePanel = new CirclePanel();
 private int dx;
 private int dy;

 public Exercise24() {
  add(circlePanel); // Add to circle panel to applet
 }

 /** Panel for displaying circles */
 class CirclePanel extends JPanel {
  private static final long serialVersionUID = 1L;

  public CirclePanel() {
   addMouseListener(new MouseAdapter() {
    @Override
    public void mouseClicked(MouseEvent e) {
     int circleNumber = isInsideACircle(e.getPoint());
     if (circleNumber == -1) {
      circles.add(new Circle(e.getX(), e.getY()));
     } else {
      circles.remove(circleNumber);
     }
     repaint();
    }
    
    @Override
    public void mousePressed(MouseEvent e) {
     int x = e.getX();
     int y = e.getY();
     for (int i = 0; i < circles.size(); i++) {
      if(getLenght(circles.get(i).x, circles.get(i).y, x, y) < circles.get(i).radius) {
       movedCircle = i;
       isMoving = true;
       dx = circles.get(i).x - x;
       dy = circles.get(i).y - y;
       break;
      }
     }
    }
    
    @Override
    public void mouseReleased(MouseEvent e) {
     isMoving = false;
    }
   });
   
   addMouseMotionListener(new MouseMotionAdapter() {    
    @Override
    public void mouseDragged(MouseEvent e) {
     if(isMoving) {
      circles.get(movedCircle).x = e.getX() + dx;
      circles.get(movedCircle).y = e.getY() + dy;
      circlePanel.repaint();
     }
    }
   });
  }

  private double getLenght(double x1, double y1, double x2, double y2){
   return Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
  }
  
  /** Returns true if the point is inside an existing circle */
  private int isInsideACircle(Point p) {
   for (int i = 0; i < circles.size(); i++) {
    if (circles.get(i).contains(p)) {
     return i;
    }
   }
   return -1;
  }

  @Override
  protected void paintComponent(Graphics g) {
   super.paintComponent(g);
   
   if (circles.size() == 0)
    return; // Nothing to paint

   // Build the edges
   List<AbstractGraph.Edge> edges = new ArrayList<AbstractGraph.Edge>();
   for (int i = 0; i < circles.size(); i++)
    for (int j = i + 1; j < circles.size(); j++)
     if (circles.get(i).overlaps(circles.get(j))) {
      edges.add(new AbstractGraph.Edge(i, j));
      edges.add(new AbstractGraph.Edge(j, i));
     }

   // Create a graph with circles as vertices
   Graph<Circle> graph = new UnweightedGraph<Circle>(edges, circles);
   AbstractGraph<Circle>.Tree tree = graph.dfs(0); // a DFS tree
   boolean isAllCirclesConnected = circles.size() == tree
     .getNumberOfVerticesFound();

   for (Circle circle : circles) {
    int radius = circle.radius;
    if (isAllCirclesConnected) { // All circles are connected
     g.setColor(Color.RED);
     g.fillOval(circle.x - radius, circle.y - radius,
       2 * radius, 2 * radius);
    } else
     // circles are not all connected
     g.drawOval(circle.x - radius, circle.y - radius,
       2 * radius, 2 * radius);
   }
  }
 }

 private static class Circle {
  int radius = 20;
  int x, y;

  Circle(int x, int y) {
   this.x = x;
   this.y = y;
  }

  public boolean contains(Point p) {
   double d = distance(x, y, p.x, p.y);
   return d <= radius;
  }

  public boolean overlaps(Circle circle) {
   return distance(this.x, this.y, circle.x, circle.y) <= radius
     + circle.radius;
  }

  private static double distance(int x1, int y1, int x2, int y2) {
   return Math.sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
  }
 }

 public static void main(String[] args) {
  JFrame frame = new JFrame();
  JApplet applet = new Exercise24();
  frame.add(applet);
  frame.setTitle("Exercise24");
  frame.setLocationRelativeTo(null);
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  frame.setSize(600, 400);
  frame.setLocationRelativeTo(null);
  frame.setVisible(true);
 }

 static class UnweightedGraph<V> extends AbstractGraph<V> {
  /** Construct an empty graph */
  public UnweightedGraph() {
  }

  /** Construct a graph from edges and vertices stored in arrays */
  public UnweightedGraph(int[][] edges, V[] vertices) {
   super(edges, vertices);
  }

  /** Construct a graph from edges and vertices stored in List */
  public UnweightedGraph(List<Edge> edges, List<V> vertices) {
   super(edges, vertices);
  }

  /** Construct a graph for integer vertices 0, 1, 2 and edge list */
  public UnweightedGraph(List<Edge> edges, int numberOfVertices) {
   super(edges, numberOfVertices);
  }

  /** Construct a graph from integer vertices 0, 1, and edge array */
  public UnweightedGraph(int[][] edges, int numberOfVertices) {
   super(edges, numberOfVertices);
  }
 }

 static abstract class AbstractGraph<V> implements Graph<V> {
  protected List<V> vertices = new ArrayList<V>(); // Store vertices
  protected List<List<Integer>> neighbors = new ArrayList<List<Integer>>(); // Adjacency
                     // lists

  /** Construct an empty graph */
  protected AbstractGraph() {
  }

  /** Construct a graph from edges and vertices stored in arrays */
  protected AbstractGraph(int[][] edges, V[] vertices) {
   for (int i = 0; i < vertices.length; i++)
    this.vertices.add(vertices[i]);

   createAdjacencyLists(edges, vertices.length);
  }

  /** Construct a graph from edges and vertices stored in List */
  protected AbstractGraph(List<Edge> edges, List<V> vertices) {
   for (int i = 0; i < vertices.size(); i++)
    this.vertices.add(vertices.get(i));

   createAdjacencyLists(edges, vertices.size());
  }

  /** Construct a graph for integer vertices 0, 1, 2 and edge list */
  @SuppressWarnings("unchecked")
  protected AbstractGraph(List<Edge> edges, int numberOfVertices) {
   for (int i = 0; i < numberOfVertices; i++)
    vertices.add((V) (new Integer(i))); // vertices is {0, 1, ...}

   createAdjacencyLists(edges, numberOfVertices);
  }

  /** Construct a graph from integer vertices 0, 1, and edge array */
  @SuppressWarnings("unchecked")
  protected AbstractGraph(int[][] edges, int numberOfVertices) {
   for (int i = 0; i < numberOfVertices; i++)
    vertices.add((V) (new Integer(i))); // vertices is {0, 1, ...}

   createAdjacencyLists(edges, numberOfVertices);
  }

  /** Create adjacency lists for each vertex */
  private void createAdjacencyLists(int[][] edges, int numberOfVertices) {
   // Create a linked list
   for (int i = 0; i < numberOfVertices; i++) {
    neighbors.add(new ArrayList<Integer>());
   }

   for (int i = 0; i < edges.length; i++) {
    int u = edges[i][0];
    int v = edges[i][1];
    neighbors.get(u).add(v);
   }
  }

  /** Create adjacency lists for each vertex */
  private void createAdjacencyLists(List<Edge> edges, int numberOfVertices) {
   // Create a linked list for each vertex
   for (int i = 0; i < numberOfVertices; i++) {
    neighbors.add(new ArrayList<Integer>());
   }

   for (Edge edge : edges) {
    neighbors.get(edge.u).add(edge.v);
   }
  }

  @Override
  /** Return the number of vertices in the graph */
  public int getSize() {
   return vertices.size();
  }

  @Override
  /** Return the vertices in the graph */
  public List<V> getVertices() {
   return vertices;
  }

  @Override
  /** Return the object for the specified vertex */
  public V getVertex(int index) {
   return vertices.get(index);
  }

  @Override
  /** Return the index for the specified vertex object */
  public int getIndex(V v) {
   return vertices.indexOf(v);
  }

  @Override
  /** Return the neighbors of the specified vertex */
  public List<Integer> getNeighbors(int index) {
   return neighbors.get(index);
  }

  @Override
  /** Return the degree for a specified vertex */
  public int getDegree(int v) {
   return neighbors.get(v).size();
  }

  @Override
  /** Print the edges */
  public void printEdges() {
   for (int u = 0; u < neighbors.size(); u++) {
    System.out.print(getVertex(u) + " (" + u + "): ");
    for (int j = 0; j < neighbors.get(u).size(); j++) {
     System.out.print("(" + u + ", " + neighbors.get(u).get(j)
       + ") ");
    }
    System.out.println();
   }
  }

  @Override
  /** Clear graph */
  public void clear() {
   vertices.clear();
   neighbors.clear();
  }

  @Override
  /** Add a vertex to the graph */
  public void addVertex(V vertex) {
   vertices.add(vertex);
   neighbors.add(new ArrayList<Integer>());
  }

  @Override
  /** Add an edge to the graph */
  public void addEdge(int u, int v) {
   neighbors.get(u).add(v);
   neighbors.get(v).add(u);
  }

  /** Edge inner class inside the AbstractGraph class */
  public static class Edge {
   public int u; // Starting vertex of the edge
   public int v; // Ending vertex of the edge

   /** Construct an edge for (u, v) */
   public Edge(int u, int v) {
    this.u = u;
    this.v = v;
   }
  }

  @Override
  /** Obtain a DFS tree starting from vertex v */
  /** To be discussed in Section 27.6 */
  public Tree dfs(int v) {
   List<Integer> searchOrder = new ArrayList<Integer>();
   int[] parent = new int[vertices.size()];
   for (int i = 0; i < parent.length; i++)
    parent[i] = -1; // Initialize parent[i] to -1

   // Mark visited vertices
   boolean[] isVisited = new boolean[vertices.size()];

   // Recursively search
   dfs(v, parent, searchOrder, isVisited);

   // Return a search tree
   return new Tree(v, parent, searchOrder);
  }

  /** Recursive method for DFS search */
  private void dfs(int v, int[] parent, List<Integer> searchOrder,
    boolean[] isVisited) {
   // Store the visited vertex
   searchOrder.add(v);
   isVisited[v] = true; // Vertex v visited

   for (int i : neighbors.get(v)) {
    if (!isVisited[i]) {
     parent[i] = v; // The parent of vertex i is v
     dfs(i, parent, searchOrder, isVisited); // Recursive search
    }
   }
  }

  @Override
  /** Starting bfs search from vertex v */
  /** To be discussed in Section 27.7 */
  public Tree bfs(int v) {
   List<Integer> searchOrder = new ArrayList<Integer>();
   int[] parent = new int[vertices.size()];
   for (int i = 0; i < parent.length; i++)
    parent[i] = -1; // Initialize parent[i] to -1

   java.util.LinkedList<Integer> queue = new java.util.LinkedList<Integer>(); // list
                      // used
                      // as
                      // a
                      // queue
   boolean[] isVisited = new boolean[vertices.size()];
   queue.offer(v); // Enqueue v
   isVisited[v] = true; // Mark it visited

   while (!queue.isEmpty()) {
    int u = queue.poll(); // Dequeue to u
    searchOrder.add(u); // u searched
    for (int w : neighbors.get(u)) {
     if (!isVisited[w]) {
      queue.offer(w); // Enqueue w
      parent[w] = u; // The parent of w is u
      isVisited[w] = true; // Mark it visited
     }
    }
   }

   return new Tree(v, parent, searchOrder);
  }

  /** Tree inner class inside the AbstractGraph class */
  /** To be discussed in Section 27.5 */
  public class Tree {
   private int root; // The root of the tree
   private int[] parent; // Store the parent of each vertex
   private List<Integer> searchOrder; // Store the search order

   /** Construct a tree with root, parent, and searchOrder */
   public Tree(int root, int[] parent, List<Integer> searchOrder) {
    this.root = root;
    this.parent = parent;
    this.searchOrder = searchOrder;
   }

   /** Return the root of the tree */
   public int getRoot() {
    return root;
   }

   /** Return the parent of vertex v */
   public int getParent(int v) {
    return parent[v];
   }

   /** Return an array representing search order */
   public List<Integer> getSearchOrder() {
    return searchOrder;
   }

   /** Return number of vertices found */
   public int getNumberOfVerticesFound() {
    return searchOrder.size();
   }

   /** Return the path of vertices from a vertex to the root */
   public List<V> getPath(int index) {
    ArrayList<V> path = new ArrayList<V>();

    do {
     path.add(vertices.get(index));
     index = parent[index];
    } while (index != -1);

    return path;
   }

   /** Print a path from the root to vertex v */
   public void printPath(int index) {
    List<V> path = getPath(index);
    System.out.print("A path from " + vertices.get(root) + " to "
      + vertices.get(index) + ": ");
    for (int i = path.size() - 1; i >= 0; i--)
     System.out.print(path.get(i) + " ");
   }

   /** Print the whole tree */
   public void printTree() {
    System.out.println("Root is: " + vertices.get(root));
    System.out.print("Edges: ");
    for (int i = 0; i < parent.length; i++) {
     if (parent[i] != -1) {
      // Display an edge
      System.out.print("(" + vertices.get(parent[i]) + ", "
        + vertices.get(i) + ") ");
     }
    }
    System.out.println();
   }
  }
 }

 interface Graph<V> {
  /** Return the number of vertices in the graph */
  public int getSize();

  /** Return the vertices in the graph */
  public java.util.List<V> getVertices();

  /** Return the object for the specified vertex index */
  public V getVertex(int index);

  /** Return the index for the specified vertex object */
  public int getIndex(V v);

  /** Return the neighbors of vertex with the specified index */
  public java.util.List<Integer> getNeighbors(int index);

  /** Return the degree for a specified vertex */
  public int getDegree(int v);

  /** Print the edges */
  public void printEdges();

  /** Clear graph */
  public void clear();

  /** Add a vertex to the graph */
  public void addVertex(V vertex);

  /** Add an edge to the graph */
  public void addEdge(int u, int v);

  /** Obtain a depth-first search tree */
  public AbstractGraph<V>.Tree dfs(int v);

  /** Obtain a breadth-first search tree */
  public AbstractGraph<V>.Tree bfs(int v);
 }

}