61 lines
1.8 KiB
Markdown
61 lines
1.8 KiB
Markdown
# Files and Java.io
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### Files
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```java
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import java.utils.*
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import java.io.*
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public void writeAnimalData( String fileName ) throws FileNotFoundException
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{
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PrintWriter pWriter = new PrintWriter( fileName );
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for( Animal a: animalCollection )
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{
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String lineOfOutput = a.getName() + "" + a.getSpecies();
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pWriter.println( lineOfOutput );
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}
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pWriter.close();
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}
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```
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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.
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The method `PrintWriter` itself, also includes the clause, as can be seen in the Java.io documentation.
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```java
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public Zoo( String fileName ) throws FileNotFoundException
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{
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this();
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readAnimalData( fileName );
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}
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```
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This allows us to use the code from the default constructor without duplicating the code. `this();` must be the first keyword in the method.
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### Scanner
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The scanner class is used to read data from the keyboard / file.
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Once a Scanner object has been created (from Java.util), data can be read: `new Scanner( System.in );`
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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:
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```java
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String name = scanner.next();
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String species = scanner.next();
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```
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#### Ex
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```java
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public void readAnimalData( String fileName) throws FileNotFoundException
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{
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File dataFile = new File( fileName ); //Create file to write to.
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Scanner scanner = new Scanner( dataFile ); //Initialise scanner.
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while( scanner.hasNext() )
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{
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String name = scanner.next(); //First token in line.
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String species = scanner.next(); //Second token in line.
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StoreAnimal( new Animal( species, name ) ); //Store the tokens as an animal in list.
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scanner.nextLine(); //Increment to next line.
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}
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scanner.close();
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}
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```
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