1. Computer Science and Engineering
Binary Decision Tree
Computer Science and Engineering
1/13/2019
B.Ramamurthy

2. Introduction
Binary Search Tree: Key value at the root partitions the set of data represented in the tree into three disjoint sets:
A set with key value at the root
A set of keys in the left subtree < key value of the root
A set of keys in the right subtree > key value of the root
We considered only numerical values, > and < operators.
In a decision tree the criteria for partition is stored in the internal node and the data in the leaf nodes. When the partition is two-way we get a binary decision tree.
Example:
Tree for the popular animal guessing game
The criteria “mammal” could split the zoo animals into two sets, such other criteria could split the two sets further, until the splitting process results in a single animal kind.
1/13/2019
B.Ramamurthy

3. (Zoo) Animal Tree Is it a mammal? no yes Is it an amphibian?
Is it a wild animal? no
yes
yes no
Frog
Parrot
Does it have a long neck?
Cow
yes no
Questions with “yes” or “no”
answers at the internal nodes;
Answers at the leaf nodes.
Giraffe
Tiger
1/13/2019
B.Ramamurthy

4. Simple Guesser: no load/save
1/13/2019
B.Ramamurthy

5. Builder/Guesser with save/no load
AnimalDBBuilder
java.io.Serializable
BTreeInterface
ObjectOutputStream
BTree
Visitor
OutputFile
LearnVisitor
PlayVisitor
1/13/2019
B.Ramamurthy

6. Guesser with simple load/save
GuesserSimpleLoadSave
java.io.Serializable
BTreeInterface
ObjectOutputStream
ObjectInputStream
BTree
Visitor
OutputFile
InputFile
LearnVisitor
PlayVisitor
1/13/2019
B.Ramamurthy

7. Guesser with Load/Save Visitors
OtherApplications
GuesserLoadSave
java.io.Serializable
BTreeInterface
ObjectOutputStream
ObjectInputStream
Visitor
BTree
OutputFile
InputFile
LearnVisitor
PlayVisitor
LoadVisitor
SaveVisitor
1/13/2019
B.Ramamurthy

8. Load/Save (using Object Streaming)
The capability to store and retrieve Java objects is essential to building persistence and streaming into application.
Writing to an Object Stream
Reading from an Object Stream
Exception Handling
Example: See the code in the BTree example
1/13/2019
B.Ramamurthy

9. Persistence
The values of the data structures in a program are lost when the program terminates.
If you want the data to exist after program termination you need to store it in a file or in a database.
This capability of data is known as persistence.
1/13/2019
B.Ramamurthy

10. How to use Serialization?
1. import java.io.*;
2. Specify the class whose instances need to be stored/loaded as implementing java.io.Serializable interface.
3. Use writeObject and readObject methods whose header are as given below:
void writeObject (Object obj) throws IOException;
Object readObject() throws ClassNotFoundException, IOException;
1/13/2019
B.Ramamurthy

11. Writing to an Object Stream
// serialize various objects into a file
FileOutputStream f = new FileOutputStream(“tmp”);
ObjectOutputStream s = new ObjectOutputStream(f);
s.writeObject(“Today”);
s.writeObject(new Date());
BTree t = new BTree(“MyName”, null, null);
s.writeObject(t);
1/13/2019
B.Ramamurthy

12. Reading from an Object Stream
// Deserialize a objects from a file
FileInputStream inf = new FileInputStream(“tmp”);
ObjectInputStream s1 = new ObjectInputStream(inf);
//read the Object and cast to retrieve the
// actual object
String = (String)s1.readObject();
Data date = (Date)s1.readObject();
BTree animalDB = (BTree)s1.readObject();
1/13/2019
B.Ramamurthy