Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Files/Spreadsheet Processing3/2/2009Opening Discussion●Midterm results. Will be returned on Wednesday. Log into grading program using your normal login name with your 7-digit ID number as the password.●Grades are subject to change. There could be a curve after extra credit problems are turned in.Objectives●We have a new topic and new goals. We are going to see how programming can let you do things with tabular data that you might have problems doing with standard programs.●First, we need to learn how to read information from a file and put it into our program.●After that we will work on processing the data.Spreadsheet Scenario●We have a new scenario that we are going to work with called spreadsheet.●This scenario has a world that shows a grid.●The grid can be filled with numbers that are drawn on the world.●What we want to do today is fill in the readFile() method so that it can read in CSV text files.Numbers with Decimals●The numbers we are dealing with might have decimals.●For that reason, we can't use the int type.●Instead we will use the double type. Double stands for double-precision floating point. These aren't real numbers in the mathematical sense, they have limited precision.●Our table uses the Double class which is a wrapper for double so it return null.Reading from File●We are going to use the java.util.Scanner class for reading from files.●Let's look at the API entry for that.●To read from a file we will use the constructor that takes a java.io.File object.●Let's look at the API entry for File.●By default Greenfoot looks for files in the directory of the current scenario.Strategy●Here is what we want to do in readFile() to read a CSV file.●Make a scanner.●While the scanner has more lines–Read a line–Split the line on commas–For each of the values●Add it to the tableExceptions●When things go wrong in Java the code throws exceptions. Files can have lots of things go wrong.●Use a try block when you want to try to do something that might throw an exception then catch that exception.–try {●Statements–} catch(ExceptionType e) {●Statements–}The while Loop●Not everything we repeat in code is well modeled by counting. Reading all the lines in a file is an example.●The while loop allows you to repeat something as long as a condition is true.●while(condition) {–Statements●}The split Method●One way to break a string up into parts is with the split(String delim) method of the String class.●You pass it the delimiter to split on and it gives you back a String[].●We will use split on the line we read and then have a for loop go through the array.Minute Essay●What are your plans for spring break?●Remember that the TA will be in class on Wednesday and Friday. He will help with midterm extra credit or whatever else you want to talk
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