Input screen        PROGRAM                Output screen  

5        THE COLLATZ PROGRAM    5,  16,  8,  4,  2 1  

red white blue    SORT WORDS            blue red white  

Remark
We want to write programs in Java that render the computer a special purpose problem solver.  

the approach we will adopt
we will write Java programs (text) by means of a ``Template based slot + filler'' scheme.

Remark
In the sole executable instruction of the ``Hello World!   '' program...   the message println ( ``Hello World!   '' ) is sent to the object IO which responds behaviorally by rinting the character string ``Hello World!   '' to the standard output file. 

Remark
One can interpret the line IO.println ( ``Hello World!   '' );  in the following way:

• IO is an object
  
• println ( ``Hello World!   '' ) is a message
  

A java program to read two integers and display their sum.
< PROGRAM > -- > / /read the two integers and store

/ /them in memory
int n1 = IO.read_int ();
int n2 = IO.read_int ();
/ /compute the sum
int sum = n1 + n2;
/ /Display the sum,  labled
IO.print ( ``the sum is:   ``);
IO.print (sum);
IO.println ();

Enviornment (bindings in memory)
n1 ---- > 12
n2 ---- > 7
sum --- > 19 

Remark
In java all variables must be introduced by specifying the type of value they can denote. 

Specification of variable Declaration
< TYP > < IDENTIFIER >
ex
int n1 = IO.read_int ();