From APIs to Programs

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Chapter 8
From APIs to Programs

   8.1 The Making of a Program
   8.2 Assigning Meaning to Programs
   8.3 General Rules
   8.4 Code Comments
   8.5 Assignment #9: Simple Programming

8.1 The Making of a Program

A program is a class which includes a ‘main’ method having the following interface.
public static void main(String[] args)
A class without a main method is an independent mechanism for introducing objects into programs.
The command ‘javac filename.java’ is available for compiling classes into executable code.
The command ‘java name’ is available for executing a program (defined by a class named ‘name’).

class trivial{
public static void main(String[] args){}
}

8.2 Assigning Meaning to Programs

Programs are processors of information
The information provided to a program is said to be its input
The information produced by a program is said to be its output
The meaning of a program is the input-output relationship defined by the program
API’s define the structural spine for programs
With well chosen names, and informative comments, APIs show the intended meaning of programs.
The actual meaning of a program is realized through code introduced to the bodies of its methods and constructors.

class helloWorld{
public static void main(String[] args){
System.out.println("Hello World!");
} }

The instruction ‘System.out.println("string")’ is among the simplest available for outputing text.

8.3 General Rules

Instructions not terminating by a braced group (of instructions) should be followed by a semicolon ‘;’.
Methods with typed return values must include a ‘return value’ in their body. The value should be compatible with the specified type.
class Bulb {
  boolean status;
  void flip (){ }
  int getAverage(){ return 1500; }
}
It is customary to use for classes names which start with a capital letter. However, program classes are exceptions. They are typically assigned names which start with a lower case letter.

8.4 Code Comments

The API comments /** ... */ are extract by the javadoc utility into the documentation
Comments of the form /* ... */ are ignored by javadoc and the other utilities. They are for local use within the code by the programmers.
A double slash // designates the remainder of the line to be a comment.

Exercises

8.5 Assignment #9: Simple Programming

Due: Fr, Apr 25, midnight

Write a program which outputs the following code.

     Ring around the rosie,
     Pocket full of posie,
     Ashes, ashes,
     We all fall down.

     Round the ring of roses,
     Pots full of posies,
     The one who stoops last,
     Shall tell whom she loves best.

Assume ‘lab9’ for the submit program, and the name roses.java for the file containing the program..

Note: Files that fail to compile, and execute when applicable, will not be examined. They will be awarded a grade of 0 points.

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