import java.awt.*; 
import java.awt.event.*; 
import javax.swing.*;
 
class DocPanel extends Panel implements ItemListener	{
	 JComboBox doc;
	 JTextArea displayArea;

	 DocPanel(JTextArea displayArea)	{ 
		  this.displayArea = displayArea;
		  //setBackground(Color.lightGray);
		  setLayout(new GridLayout(3, 1, 0, 5));
		  
		  //pull down menu for guidelines
		  add(new JLabel("Documentation")); 
          String [] docStrings = {"Introduction", "2-Node", "3-Node", "4-Node", "Properties"};
		  doc = new JComboBox(docStrings);
		  // doc.addItem("Introduction"); 
		  // doc.addItem("2-Node"); 
		  // doc.addItem("3-Node"); 
		  // doc.addItem("4-Node");
		  // doc.addItem("Properties");
		  // doc.addItem("Run algorithm");
		  // doc.addItem("Step algorithm"); 
		  doc.addItemListener(this); 
		  add(doc);
	 }
	 
	 public void itemStateChanged(ItemEvent ie)	{
		  String str = (String)ie.getItem();
		  if (str.equals("Introduction"))  displayArea.setText(tree);
		  else if (str.equals("2-Node")) displayArea.setText(Twonode);
		  else if (str.equals("3-Node")) displayArea.setText(Threenode);		 
		  else if (str.equals("2-3-4 Trees"))  displayArea.setText(tree); 
		  else if (str.equals("Properties"))  displayArea.setText(properties); 
	 } 
 	 
	 final String tree  = new String("What is a 2-3-4 tree ?\n"+ 
												"A 2-3-4 Tree is a special form of a B-Tree. This name derives from the fact that\n"+ 
												"each internal node has degree two, three or four children. These trees allow\n"+ 
												"insertion, deletion and searching in O(log n) time.\n"); 
	 
	 final String Twonode = new String("What is a 2-node ?\n"+ 
												  "A degree 2 node is called a 2-Node. It has only one key namely Left Key and\n"+ 
												  "two children namely Left child and Middle child.");  
	 
	 final String Threenode = new String("What is a 3-node ?\n"+ 
													 "A degree 3 node is called a 3-Node. It has two keys namely Left Key and\n"+ 
													 "Right Key. It has three children namely Left child, Middle child and\n"+ 
													 "Right Child."); 
	 
	 final String properties = new String("Properties of 2-3-4 Trees:\n" + 
													  "A 2-3-4 Tree is a search tree that is either empty or satisfies the following 4 properties:\n"+ 
													  "1. Each internal node has two, three and four children only.\n"+ 
													  "2. The height of all the leaves/external nodes is the same.\n"+
													  "3. Let Lchild and Mchild denote the children of a 2-Node. Let Lkey be the\n"+ 
													  "   only element present in this node. All elements in the sub 2-3-4 Tree with\n"+ 
													  "   root Lchild have key less than Lkey, while all elements in the sub 2-3-4 Tree\n"+ 
													  "   with root Mchild have key greater than Lkey.\n"+ 
													  "4. Let Lchild, Mchild and Rchild denote the children of a 3-Node. Let Lkey\n"+ 
													  "   and Rkey be the two elements in this node. Then, Lkey < Rkey, all keys\n"+ 
													  "   in the sub 2-3-4 Tree with root Lchild are less than Lkey, all keys in the\n"+ 
													  "   sub 2-3-4 Tree with root Mchild are less than Rkey and greated than Lkey,\n"+ 
													  "   and all keys in the sub 2-3-4 Tree with root Rchild are greater than Rkey.\n"+ 
													  "5. All external/leaf nodes are at the same level."); 
	 
	 final String whatNext = 
		  "1. INSERT: To insert a key, click on the Insert button.\n"+ 
		  "2. DELETE: To delete a key, click on the Delete button.\n"+ 
		  "3. SEARCH: To search for a key, click on the Search button.\n";
	 final String invalid = 
		  "Invalid key input:\n"+
		  "You have entered an invalid key value. Only two digit numbers are valid key values.";
	 
}