G4G0-1/Semester 2/Programming 2/Week 1/Week 1 Programming 2.md

Files and Java.io

Files

import java.utils.*
import java.io.*
public void writeAnimalData( String fileName ) throws FileNotFoundException
{
	PrintWriter pWriter = new PrintWriter( fileName );
	for( Animal a: animalCollection )
	{
		String lineOfOutput = a.getName() + "" + a.getSpecies();
		pWriter.println( lineOfOutput );
	}
	pWriter.close();
}

Without using throws FileNotFoundException, a compilation error will occur. Any method that may possibly throw an exception must advertise this by using throws to discard the error to avoid a crash. The method PrintWriter itself, also includes the clause, as can be seen in the Java.io documentation.

public Zoo( String fileName ) throws FileNotFoundException
{
	this();
	readAnimalData( fileName );
}

This allows us to use the code from the default constructor without duplicating the code. this(); must be the first keyword in the method.

Scanner

The scanner class is used to read data from the keyboard / file. Once a Scanner object has been created (from Java.util), data can be read: new Scanner( System.in ); A Scanner object breaks the input into tokens separated by whitespaces. Each line of data in the file can be easily read with the following:

String name = scanner.next();
String species = scanner.next();

Ex

public void readAnimalData( String fileName) throws FileNotFoundException
{
	File dataFile = new File( fileName ); //Create file to write to.
	Scanner scanner = new Scanner( dataFile ); //Initialise scanner.
	while( scanner.hasNext() )
	{
		String name = scanner.next(); //First token in line.
		String species = scanner.next(); //Second token in line.
		StoreAnimal( new Animal( species, name ) ); //Store the tokens as an animal in list.
		scanner.nextLine(); //Increment to next line.
	}
	scanner.close();
}