CSE205 Lecture 24

Object-Oriented Programming and Data Structures
Serialization
(202111)

Transcript

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   CSE 205
   Object-Oriented Programming and
   Data Structures
   Lecture 24: Streams and Exceptions
   Dr. Javier Gonzalez-Sanchez
   javiergs@asu.edu
   javiergs.engineering.asu.edu | javiergs.com
   PERALTA 230U
   Office Hours: By appointment
   

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   Streams
   

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3. Javier Gonzalez-Sanchez | CSE205 | Fall 2021 | 3
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   Where we are …
   Data Structures
   Files
   

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   I/O Streams
   § An I/O Stream represents an input source or an output destination
   

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   Hierarchy
   

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6. Javier Gonzalez-Sanchez | CSE205 | Fall 2021 | 6
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   File Stream (binary data)
   import java.io.FileInputStream;
   import java.io.FileOutputStream;
   import java.io.IOException;
   public class CopyBytes {
   public static void main(String[] args) {
   try {
   FileInputStream in = new FileInputStream(”myfile.txt");
   FileOutputStream out =new FileOutputStream("outagain.txt");
   int c;
   while ((c = in.read()) != -1) {
   out.write(c);
   }
   in.close();
   out.close();
   } catch (IOException e) {
   System.out.println(“Failure!”);
   }
   }
   }
   

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   File Stream (char data)
   import java.io.FileReader;
   import java.io.FileWriter;
   import java.io.IOException;
   public class CopyCharacters {
   public static void main(String[] args) {
   try {
   FileReader inputStream = new FileReader(”myFile.txt");
   FileWriter outputStream = new FileWriter(”output.txt");
   int c;
   while ((c = inputStream.read()) != -1) {
   outputStream.write(c);
   }
   inputStream.close();
   outputStream.close();
   } catch (IOException e) {
   System.out.println(“Failure!”);
   }
   }
   }
   

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8. Javier Gonzalez-Sanchez | CSE205 | Fall 2021 | 8
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   File Stream (string data)
   import java.io.FileReader;
   import java.io.FileWriter;
   import java.io.BufferedReader;
   import java.io.PrintWriter;
   import java.io.IOException;
   public class CopyLines {
   public static void main(String[] args) {
   try {
   FileReader input = new FileReader(”myFile.txt");
   FileWriter output = new FileWriter(”output.txt");
   BufferedReader inputStream = new BufferedReader(input);
   PrintWriter outputStream = new PrintWriter(output);
   String l;
   while ((l = inputStream.readLine()) != null) {
   outputStream.println(l);
   }
   inputStream.close();
   outputStream.close();
   } catch (IOException e) {
   System.out.println(“Failure!”);
   }
   }
   }
   

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   Exceptions
   try – catch statement
   

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10. Javier Gonzalez-Sanchez | CSE205 | Fall 2021 | 10
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    Exceptions
    § When executing Java code, different errors can occur due to wrong input, or
    other unforeseeable things.
    § When an error occurs, Java will normally stop and generate an error
    message.
    The technical term for this is: Java will throw an exception (an error).
    § The try statement allows you to define a block of code to be tested for
    errors while it is being executed.
    § The catch statement allows you to define a block of code to be executed, if
    an error occurs in the try block.
    § The try and catch keywords come in pairs.
    

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11. Javier Gonzalez-Sanchez | CSE205 | Fall 2021 | 11
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    try-catch Statements
    try {
    // Block of code to try
    } catch(Exception e) {
    // Block of code to handle errors
    }
    

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    Example
    

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    Exceptions
    There are many exception types available in Java:
    § ArithmeticException,
    § FileNotFoundException,
    § ArrayIndexOutOfBoundsException,
    § SecurityException,
    § etc.
    § The parent of all is the class Exception
    

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    Example
    

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    finally Statement
    § The finally statement lets you execute code, after try...catch,
    regardless of the result
    

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    Example
    

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    throw
    

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    Definition
    § The throw statement allows you to create a custom error
    

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    Example
    

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    Example
    

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22. Javier Gonzalez-Sanchez | CSE205 | Fall 2021 | 22
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    Questions
    

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    CSE 205 Object-Oriented Programming and Data Structures
    Javier Gonzalez-Sanchez, Ph.D.
    javiergs@asu.edu
    Fall 2021
    Copyright. These slides can only be used as study material for the class CSE205 at Arizona State University.
    They cannot be distributed or used for another purpose.
    

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