Lecture 1

Introduction,Administration, and Procedural Programming

  
Introduction:  
  About me: short bio  
  About Alan:  
  About the course:  
    Administration:  
       Lectures M-F 10-11:30  
       Recitation M 3:30, T-F 1:00  
       Problem Sets: 4 total,   
           programming exercises at first, then projects  
       Quizzes: Quiz 1: Wed Jan 11 Evening (covers PS1)  
                Quiz 2: Sun Jan 21 4 PM (covers PS2)  
                Note: Quiz 1 is on Wed evening to allow for grading and  
		return of PS1 before Quiz1.  
  
    Coverage and goals:  
       Title: OOP in Java  
       Goals: Teach good programming skills, technique, and practice. Not  
               primarily a course in Java (though you will learn it). Nor  
	       a course in OOP philosophy (though we will cover it). We will  
	       emphesize general principles behind OOP, programming methods  
	       and languages. Need to be able to apply principles in different  
	       circumstances, using different languages. We will focus on  
	       the pragmatic and (as much as possible), the universal.  
       Coverage: 3 major sections.  
            Basic Programming constructs  
	      Procedural programming: types, structured control.  
	      OOP: Classes, inheritance, and interfaces.  
	      Exception handling  
            Common programming paradigms: current practice  
	      I/O programming  
	      Event-based programming  
	      GUI and graphics programming  
	      MultiThreaded Programming  
	      Network Programming  
	      Asynchronous, Re-entrant and Distributed Programming: RPC etc.  
	    Design and cultural topics  
	      Program design and methodogies  
	       Class design and relationships: UML    
	       Design patterns, anti-patterns, etc.  
	       Project/program development cycle  
	      Documentation  
	      Testing  
	    Advanced programming topics  
	      Components: JavaBeans, Controls, EJB, scripting, etc.  
	      OOP in C/C++  
	      I18N and L10N  
	      Persistance and serialization  
	      Intro to Windows  
	      Java Web Programming  
  
  
OOP and Java:  
  About OOP:  
         Latest in a long line of programming styles or fads, from structured  
	     programming, modular programming, abstract data types, OOP. These  
	     appear periodically like diet fabs or self-help fabs. Each new  
	     system promises to revolutionize programming, eliminate bugs,  
	     ensure projects finish under busget and on-time, and guarantee  
	     thin thighs in 30 days. OOP has been the methodology-du-jour for  
	     some time now and there is little evidence things have radically  
	     changed. New methodologies are constantly appearing, design   
	     patterns, Anti-Patterns, Extreme Programming (best name I think).  
  
	     Although the fad/movement aspect of these techniques can be   
	     distracting and can lead to long ideological discussions (software  
	     developers have a tendency towards doctrine), they are not without  
	     merit. There are elements of good practice in all of these (just  
	     as eating well and exercising are good ideas even if you aren't  
	     in the Zone). It is our goal to extract and present these with  
	     a minimum of ideology.  
  
  About Java:  
       Java is an Object-Oriented language developed by Sun Microsystems. In  
       it's short history it has been re-marketed several times. Originally  
       designed as a language for programming computing appliances, it was  
       re-targeted around applets in the early days of the Web. The advantage  
       of Java for this task lay in it's platform independence. As applets  
       failed to gain widespread traction, Java was re-marketed as a   
       replacement for C++ in enterprise software development. It's features  
       being it's simplified semantics, memory management, and again  
       portability. It has made some small inroads in this area but far  
       from dominant (or even significant). Currently, the most action in  
       the Java world seems to be around server-side Web programming.  
  
       Despite its currently limited role in the application development  
       space, Java is a good language for learning OOP. It is considerably  
       less complex than C++, yet keeps low-level details (such as memory  
       management) from being distracting. The main danger of Java is that  
       one gets too used to things being easy and hidden and become unable  
       to function in a less supportive and protective environment.  
  
       One more note: Although Java is usually thought of as a language. It  
       is really 3 things: a language, a set of libaries,and a run-time  
       environment that supports the language and iteracts with the  
       actual underlying platform (UNIX, Windows, etc). You will see this,  
       for example,in the way Java maps classes to files and class names   
       to file paths.  
  
  
  About Programming Languages:  
       This is probably a good time for a brief overview of the space  
       of programming languages one is likely to see.  
  
                       Performance  EaseofUse   Typing  StorageMgnt    Objects  
  
       C/C++              High        Low       Strong    Explicit        C++  
       Fortran  
  
       Java               Med/Low     Med       Strong     GC             Yes  
       VB		                                   ??  
       (Lisp,Scheme)  
  
  
       JavaScript         Med/low     High      Weak       GC           Sort-of  
       Perl               Med/low     VHigh     No         GC           Sort-of  
       Tcl                Med/low     High      Weak       GC           Sort-of  
  
  
       Feature: C/C++/Java/JavaScript/Perl all have very similar syntax.  
  
  
  
Introduction to Procedural Programming: (or C programming in 30 minutes).  
  
  Main differences between "procedural" languages vs.  Scheme.  
      -Strong typing  
      -Infix syntax and {},; delimitation.  
      -Lexical scoping  
      -Support for and bias toward explicit iteration rather than recursion.  
      -Procedural, side-effect oriented style (as opposed to functional)  
      -Heap storage more visible and varied: objects (in contrast to lists)  
  
  Variables  
  
       {  
          int count=1;  
	  double value = 3.0;  
  
	  ... code here ...  
  
	  char = 'c';  
	  int foo;             // danger! uninitialized variable  
  
	  {  
	    int y=3;  
	    int count;         // Error, cannot shadow vars in enclosing blocks  
	    ... more code here ...  
  
	  }  
          ... more code here ...  
       }  
  
       Notes:  
        - statements are terminated with ;  
        - {} are used to delimit blocks (compound statements)  
        - // used for end-of-line comments. C /* ... */ syntax also allowed  
        - variables must be defined before use.    
	- variables can be defined anywhere in block.  
	   - unlike C which required definitions at top.  
	- variables can be initialized with '='  
	- variables don't have to be initialized, but they should be.  
	- variables are defined with 'types'  
  
  Types  
     - 'types' specify partial information about a variable's value. Ex.  
           we know it's an integer, not a character string, but we don't  
	   know which one.  
     - Types are used by compiler to perform error checking on programs  
         Eg. Makes sure you don't multiply a number and a string.  
     - Types also define size of storage to be allocated.  
     - Java has a number of built-in basic types:  
         boolean - true or false  
	 byte,short,int,long - 1,2,4,8 byte signed integers  
	     - note diffs with C/C++  
	 float,double - 4 and 8 byte floating point numbers  
	 char - character type (Unicode); not convertable to int  
	 void - no type, used to type functions that don't return a value  
     - Java also supports array types (more in recitation).  
     - As well as basic types, Java supports Object types (more tomorrow)  
        - object support lets programmings extend the type system and  
	  take advantage of the type checking (as well as other benefits).  
             
  Variable Scoping  
     - Variable are either local variables (local to some method) or  
        instance/class variables. There are no global variables per-se  
	in Java.  
     - Local variables are allocated on the stack and scoped to the  
        enclosing block. The extent of local variables is the local block.  
	Note: The extent of a reference variable and the object it references  
	are different!  
     - Instance variables we discuss tomorrow.  
  
  Expressions  
    - combine variables and constants   
    - expressions evaluate to (typed) value  
    - expression syntax is infix operator syntax (ie normal math syntax).  
       Ex. a+3, b*7  
    - Operator overview  
       Arith        +,-,*,/,%        number -> number  
       Logical      &&,||,^          boolean -> boolean  
       Comp         ==,!=,>,<,>=,<=  number -> boolean         
       Bit          |,&,~,<<,>>      number->number  
       SideEffect   ++,--            number->number w/ assignment  
       Assignment   = , += , -=      number->number w/ assignment  
  
    - Operators have precedence (as in math), don't rely on this. Use  
       parens to explicitly structure.  
         Ex.  (a+b)*34   
  
    - Type conversion: Automatically converts integers -> float -> double  
        as needed.  Ex.  (2.4 * 2) -> 4.8  (a double)  
	- Be care with conversion: rounding and overflow can cause errors.  
  
   Control Flow  
  
    Basic conditional: if,elseif,else  
     -syntax  
  
     if(..condition..) {  
       .. code executed if condition is true  
     }  
     else{  
       .. code executed if condition is false  
     }  
  
     - condition must evaluate to a boolean type   
          - no fooling around as in C/C++  
     - else clause is optional  
     - if branch code is single statement, the {} are not required.  
       - Be careful, if later a second statement is added only one  
         will be considered inside the 'if'. Best to always use {}.  
     - The 'else' associated with closest 'if' when ambiguous. Use  
       delimiters to avoid ambiguity  
  
        /* Bad and confusing */  
          if(cond1)               
	   if(cond2)  
              statement1  
	   else                 // assoc with cond2 if  
              statement2  
  
        /* Clearer */  
          if(cond1){  
	   if(cond2){  
              statement1  
	   }  
	   else                 // assoc with cond2 if  
              statement2  
	   }  
          }  
  
  
     - can chain if, else if to test multiple alternatives  
  
           if(cond1){  
              statement1  
           }  
	   else if(cond2){  
              statement2  
	   }  
	   else if(cond3){  
              statement3  
	   }  
	   else {  
              statement4  
	   }  
  
     - there are often better ways to implement chains like this  
  
    For loop  
  
    -syntax  
  
      for(initialization;condition;incrment){  
           ..loop code..  
      }  
      ..code after loop..  
  
    -initialization and increment are statements  
    -condition is an expression that evaluates to a boolean  
    - Semantics  
      1) execute initialization  
      2) evaluate condition  
      3) if false, jump to code after loop  
      4) if true, execute loop code, then execute increment  
      5) goto 2)  
    - continue and break statements provide fine control on loops  
        - break -- leave loop immediately (goto code after loop)  
	- continue -- stop executing loop code, jump to increment   
	                and condition test  
  
    -common patterns: counting loop  
  
      for(i=0;i<N;i++){  
        ..loop code..  
      }  
        
      - executes N times (assuming no breaks or assignments to i)  
         - i goes from 0 to N-1 in loop  
	 - i == N when loop terminates  
      - numerical pgmrs like to start loops at 1, be careful to avoid  
        fencepost errors.  
      - Be consistant in your loops (eg, start from 0, count up).  
      - Don't alter loop variable in loop code (too confusing)  
  
    -common patterns: next loop   
      for(i=first;i!=null;i = i.getNext()){  
        ..loop code..  
      }  
      - used to follow a chain of links data structures  
        Ex. cdr'ing down a linked list.  
  
    -probably 99% of all for loops you write will follow these patterns  
  
  
    While loop  
  
    -syntax  
  
    while(condition){  
       ..code to execute..  
    }  
  
    -semantics  
      1) evaluate condition  
      2) if false, exit loop  
      3) if true, execute loop code  
      4) goto 1)  
  
    -equivalent to for(;condition;){}  
      
    - loop code (or external input), must affect 'condition' value  
       (or else we loop forever).  
  
    Functions  
  
     - Java does not have glocal functions per-se (too ideologically pure).  
     - Static methods are semanticly equivalent.  
     - Ignore strange syntax for now.  
  
     public static int square(int x){  
        return(x*x);  
     }  
  
     - Argments and return values must be typed  
     - Static keyword indicates global scope  
     - public keyword indicates accessability  
     - methods can be called from within defining class with method name  
  
     // Calling square within calls  
     int x = 4;  
     int sq = square(x);       // This x is different than formal param in  
                               //   square def'n  
  
  
     - function names  can be overloaded by types  
  
     // calling square on a float will call this method  
     public static float square(float x){  
        return(x + 3.0);         // return wrong value just for fun.  
     }  
  
  
  
Putting it all together: Hello World  
  
   - When dealing with new language, always do "hello world"  
  
  public class Hello{  
     public static void main(String[] args){  
        // real code goes here  
        System.out.println("Hello World");  
     }    
  }  
  
   - Java makes some simple things hard. Ignore magic for now.  
   - Java allows one public class per file. If class is named Hello,  
      the source file MUST be named Hello.java  
   - To compile: javac Hello.java  
   - To run: java Hello  
     - should type Hello World on console  
     
One more: Recursive fact  
  
  public class FactTest{  
  
     public static int fact(int a){  
        if(a <= 1) return(1);  
	return(a * fact(a-1));  
     }  
  
     public static void main(String[] args){  
	int x = 7;  
	// println() converts int to string, adds \n  
	// Can use '+' to concatente strings  
        System.out.println("Fact of " + x + " is " + fact(x));  
  
     }    
  }  
  - This should print out 'Fact of 7 is 5040' on the console.  

  
  
Recitation:  
  
     Reference types: should be familiar from Scheme  
     Arrays and array variables  
       - concentrate on static arrays for now, (ie no 'new')  
     Reference types and aliasing (sharing structure)  
     Switch  
     Named break if time.