Lecture 4. A Real Java Program!! Generic Program Template. You first Java programs. Program design guidelines. Examples.

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1 Lecture 4 A Real Java Program!! // program to demonstrate the use of the String class methods class Ex_2 { You first Java programs. Program design guidelines. Examples. Material from Holmes Chapter 2. 1 public static void main(string[] args) throws IOException { // declarations String word, part; // instructions System.out.print("Type in the given string please: "); word = new String( keyboard.readline() ); part = word.substring(0,1); part = part.touppercase(); System.out.print("So the word is " + part.concat(word.substring(1,word.length()))); 11 Generic Program Template Comments on Holmes pp // Comments on what the program does class Dummy { BufferedReader ( new InputStreamReader ( System.in ) ); public static void main (String[] args) throws IOException { // declarations // instructions // chap_2\ex_3.java // program to calculate the circumference and // area of a circle class Ex_3 { BufferedReader(new InputStreamReader(System.in)); public static void main(string[] args) throws IOException { // data declarations float radius, circumference, area; // prompt and input radius System.out.print("Input radius "); System.out.flush(); radius = new Float(keyboard.readLine()).floatValue(); // calculate circumference and area circumference = 2.0f * (float) Math.PI * radius; area = (float) Math.PI * radius * radius;

2 // display statistics of circle System.out.println("Statistics of Circle\n"); System.out.println("Radius " + radius); System.out.println("Circumference " + circumference); System.out.println("Area " + area); Playtime 1. Write a program that computes the area of a regular polygon, given its apothem and the number of sides. Playtime 2. (Harder) Write a program that computes the area of a regular polygon, given its radius and the number of sides. Program Implementation Editor Compiler Interpreter text Results Data A Data Flow Diagram (DFD) for the implementation process import java.i0.*; Regular Polygons triangle square pentagon exagon eptagon the radius of a polygon is the segment from the centre of the polygon to one of its vertices. the apothem of a polygon is the segment from the centre of the polygon to the middle point of any of its sides. class LessSimple { // global declarations public static void main (String[] args) throws IOException { // declarations int A; ont b; int c; // instructions System.out.print("Input the first integer number: "); a = new Integer( keyboard.readline() ).intvalue(); System.out.print("Input the second integer number: "); b = new Integer( keyboard.readline() ).intvalue(); c = a + b System.out.println("The result of adding " + a + " and " b + " is the number " + c);

3 simplest2]$ javac LessSimple.java LessSimple.java:20: ; expected c = a + b LessSimple.java:1: package java.i0 does not exist import java.i0.*; LessSimple.java:5: cannot resolve symbol symbol : class BufferedReader LessSimple.java:8: cannot resolve symbol symbol : class IOException public static void main (String[] args) throws IOException { LessSimple.java:6: cannot resolve symbol symbol : class BufferedReader LessSimple.java:6: cannot resolve symbol symbol : class InputStreamReader 18-2 Software Development Unless you re familiar with programming already, probably the most popular question that comes to your mind at this stage is: How am I going to do it? No panic! This is one of the major skills in our job and there are methods to learn it. 19 LessSimple.java:12: cannot resolve symbol symbol : class ont ont b; LessSimple.java:17: cannot resolve symbol symbol : variable a a = new Integer( keyboard.readline() ).intvalue(); LessSimple.java:20: cannot resolve symbol symbol : variable a c = a + b 9 errors Program Design Problem analysis. Studying the nature of the problem. Algorithm. (This is the creative step) Invent a way to solve it. Data Dictionary. List the data you need. Desk Check. Using traces, check the correctness of your program. Screen Layout. Decide how the output should look. Coding. Type in your program. Test results. After successful compilation, check that you get correct results. Let s look at a couple of examples

4 Case Study: Time Taken to Fill a Swimming Pool Problem. Write a program to input the length, width and depth of a rectangular swimming pool of uniform depth and calculate the time it takes to fill it. Assume the rate of flow of water into the pool is 50 liters per minutes and that 1 cube meter has a capacity of 1,000 liters of water. Problem Analysis. The solution involves computing the volume of the swimming pool (in cube meters) and multiply it by 1,000 to obtain the capacity of the pool. The time taken to fill that up is then computed by dividing the total capacity by the rate of flow. We can refine each of the steps (this is called stepwise refinement): 1. input the size of the pool (a) input length (b) input width (c) input depth 2. calculate the volume of the pool (a) volume = length width depth. 3. calculate the time to fill the pool (a) capacity = volume capacity per cube meter. (b) time = capacity rate of flow. 4. output the results (a) output the volume of the pool (b) output the capacity of the water in liters (c) output the time to fill the pool Data Dictionary. Decide what variables to use and of which type. Algorithm. Quite straightforward. At a high level of abstraction. 1. input the size of the pool 2. calculate the volume of the pool 3. calculate the time to fill the pool 4. output the results // rate of water flow into pool is 50 liters per minute final float RATE_OF_FLOW = 50.0f; // cubic meter of water has a capacity of 1,000 liters! final float CAPACITY = f; float lengthofpool; float widthofpool; float depthofpool; float volumeofpool; float capacityofpool; float timetofillpool; 22 23

5 // chap_2\ex_4.java // program to calculate the time to fill a swimming pool class Ex_4 { BufferedReader(new InputStreamReader(System.in)); public static void main(string[] args) throws IOException { // rate of water flow into pool is 50 liters per minute final float RATE_OF_FLOW = 50.0f; // One cubic meter of water has a capacity of 1,000 liters! final float CAPACITY = f; float lengthofpool, widthofpool, depthofpool; float volumeofpool, capacityofpool, timetofillpool; // input size of pool System.out.println("Input dimensions of Swimming Pool\n"); System.out.print("Length? "); System.out.flush(); lengthofpool = new Float(keyboard.readLine()).floatValue(); System.out.print("Width? "); System.out.flush(); widthofpool = new Float(keyboard.readLine()).floatValue(); System.out.print("Depth? "); System.out.flush(); 23-1 Case Study: Average Price of Fuel Consumption Problem. Write a program to input the cost of fuel put in the car each day of the week, then compute the total cost and the average cost (in pounds), and display the results of the two computations. Problem Analysis. The input stage need to present the user with the days of the week and wait for the user to input the appropriate amount of money. Then the total cost of the fuel is simply the sum of seven different costs and the average is the total cost divided by seven. 24 depthofpool = new Float(keyboard.readLine()).floatValue(); // calculations volumeofpool = lengthofpool * widthofpool * depthofpool; capacityofpool = volumeofpool * CAPACITY; timetofillpool = capacityofpool / (RATE_OF_FLOW * 60); // display information System.out.println("\nStatistics of Swimming Pool\n"); System.out.println("Volume \t" + volumeofpool + " cubic meters"); System.out.println("Capacity \t" + capacityofpool + " liters"); System.out.println("Filling time\t" + timetofillpool + " hours"); Algorithm. 1. input data for fuel cost (a) input Monday s cost (b) input Tuesday s cost (c) input Wednesday s cost (d) input Thursday s cost (e) input Friday s cost (f) input Saturday s cost (g) input Sunday s cost 2. calculate costs (a) calculate total cost by summing the daily costs; (b) calculate the average cost by dividing the total by seven. 3. output results (a) display total cost (b) display average cost

6 // the computation totalcost = MondayCost + TuesdayCost + WednesCost + ThursCost + FridayCost + SaturdayCost + SundayCost; avgcost = totalcost / 3; Data Dictionary The seven days of the week can be displayed on the screen when asking for the data. We need seven variables for the fuel cost in each day and two more variables one for the total and the other for the average cost: // the output section System.out.println("\nStatistics about fuel costs\n"); System.out.println("Total price " + totalcost + " pounds"); System.out.println("Average price " + avgcost + " pounds"); double MondayCost, TuesdayCost, WednesCost, ThursdayCost, FridayCost, SaturdayCost, SundayCost; double totalcost, avgcost; // chap_2\ex_5.java // program to input the cost of fuel each day of the week, // calculate and display the total cost of the fuel and the // average price (per day) class Ex_5 { BufferedReader(new InputStreamReader(System.in)); public static void main(string[] args) { double MondayCost, TuesdayCost, WednesCost, ThursCost, FridayCost, SaturdayCost, SundayCost; double totalcost, avgcost; // the input section System.out.println("Input data on fuel prices\n"); System.out.print("How much did you spend on Monday? ") System.out.flush( MondayCost = new Double(keyboard.readLine()).doubleValue(); System.out.print("And on Tuesday? "); System.out.flush(); TuesdayCost = new Double(keyboard.readLine()).doubleValue();... Tutorial. Type in, compile and run all the programs we have looked at and convince yourself that they work. Important! This is the way any programming assignment should be solved! Your submission should include all ingredients we have seen in these examples: problem statement, analysis, algorithmic solution, data dictionary and code, plus a number of tests to check that the program works