1

Hi

This code not run :

it show this error: incompatible types-found java.lang.String but expected HuffmanCodingAnimation.Node

This line of code`root.left.code = root.code + "0";`

Here is the code:

```
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.tree.*;
/*
* This program enables a user to enter text and displays the Huffman coding tree based on the entered text.
*
* The display shows the weight of the subtree inside a subtree's root circle. The character is displayed at each leaf node.
* The encoded bits are displayed for the text in the dialog box.
* The decoded text button is used to decode a string of bits int text.
*/
public class HuffmanCodingAnimation extends JApplet {
private static final long serialVersionUID = 1L;
private TreeView treeView = new TreeView();
private Tree tree;
public HuffmanCodingAnimation(Tree final_tree) {
tree = final_tree;
add(new JScrollPane(treeView));
treeView.setTree(tree);
String[] codes = getCode(tree.root);
}
/** Decode the bit string into a text */
public String decode(String bits) {
String result = "";
Node p = tree.root; // Start from the root
for (int i = 0; i < bits.length(); i++) {
if (bits.charAt(i) == '0')
p = p.left;
else if (bits.charAt(i) == '1')
p = p.right;
else
return null; // Wrong bits
if (p.left == null)
{ // A leaf detected
result += p.character;
p = tree.root; // Restart from the root
}
}
return result;
}
/** Encode the text using the codes */
public static String encode(String text, String[] codes) {
String result = "";
for (int i = 0; i < text.length(); i++)
result += codes[text.charAt(i)];
return result;
}
class Tree extends JPanel {
public Node root;
}
class Node extends JPanel {
public Node character;
public Node right;
public Node code;
public Node left;
public Node frequency;
}
/** Get Huffman codes for the characters
* This method is called once after a Huffman tree is built
*/
public static String[] getCode(Node root) {
if (root == null) return null;
String[] codes = new String[2 * 128];
assignCode(root, codes);
return codes;
}
/* Recursively get codes to the leaf node */
private static void assignCode(Node root, String[] codes) {
if (root.left != null) {
root.left.code = root.code + "0";
assignCode(root.left, codes);
root.right.code = root.code + "1";
assignCode(root.right, codes);
}
else {
codes[(int)root.character.charAt(0)] = root.code;
}
}
// Inner class TreeView for displaying a tree on a panel
class TreeView extends JPanel {
private static final long serialVersionUID = 1L;
private int radius = 20; // Tree node radius
private int vGap = 50; // Gap between two levels in a tree
Tree tree;
public TreeView() { }
public TreeView(Tree tree)
{
this.tree = tree;
}
public void setTree(Tree tree) {
this.tree = tree;
repaint();
}
protected void paintComponent(Graphics g) {
super.paintComponent(g);
if (tree == null) return;
if (tree.root != null) {
// Display tree recursively
displayTree(g, tree.root, getWidth() / 2, 30, getWidth() / 4);
}
}
/** Display a subtree rooted at position (x, y) */
private void displayTree(Graphics g, Node root, int x, int y, int hGap)
{
// Display the root
g.drawOval(x - radius, y - radius, 2 * radius, 2 * radius);
g.drawString(root.frequency + "", x - 6, y + 4);
if (root.left == null) // Display the character for leaf node
g.drawString(root.character + "", x - 6, y + 34);
if (root.left != null) {
// Draw a line to the left node
connectLeftChild(g, x - hGap, y + vGap, x, y);
// Draw the left subtree recursively
displayTree(g, root.left, x - hGap, y + vGap, hGap / 2);
}
if (root.right != null) {
// Draw a line to the right node
connectRightChild(g, x + hGap, y + vGap, x, y);
// Draw the right subtree recursively
displayTree(g, root.right, x + hGap, y + vGap, hGap / 2);
}
}
/** Connect a parent at (x2, y2) with
* its left child at (x1, y1) */
private void connectLeftChild(Graphics g, int x1, int y1, int x2, int y2) {
double d = Math.sqrt(vGap * vGap + (x2 - x1) * (x2 - x1));
int x11 = (int)(x1 + radius * (x2 - x1) / d);
int y11 = (int)(y1 - radius * vGap / d);
int x21 = (int)(x2 - radius * (x2 - x1) / d);
int y21 = (int)(y2 + radius * vGap / d);
g.drawLine(x11, y11, x21, y21);
g.drawString("0", (x11 + x21) / 2 - 5, (y11 + y21) / 2);
}
/** Connect a parent at (x2, y2) with
* its right child at (x1, y1) */
private void connectRightChild(Graphics g, int x1, int y1, int x2, int y2) {
double d = Math.sqrt(vGap * vGap + (x2 - x1) * (x2 - x1));
int x11 = (int)(x1 - radius * (x1 - x2) / d);
int y11 = (int)(y1 - radius * vGap / d);
int x21 = (int)(x2 + radius * (x1 - x2) / d);
int y21 = (int)(y2 + radius * vGap / d);
g.drawLine(x11, y11, x21, y21);
g.drawString("1", (x11 + x21) / 2 + 5, (y11 + y21) / 2);
}
public Dimension getPreferredSize() { return new Dimension(300, 300);}
} //end class TreeView
}
```

// please Help me