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Strings and File I/O
Strings
• Java String objects are immutable
• Common methods include:
– boolean equalsIgnoreCase(String str)
– String toLowerCase()
– String substring(int offset, i nt endIndex)
– String replace(char oldChar, char newChar)
– int indexOf(String str)
File Input (Text)
• Option 1: Scanner/File
– Scans input from given File
– Input from file instead of System.in ( keyboard)
– Easy to scan ints, doubles, etc
• Option 2: BufferedReader/FileReader
– BufferedReader allows you to read a line at a
time instead of a character
File Input (Text)
• Option 1: Scanner
Scanner scan = new Scanner(new File(”myfile.txt"));
String s;
while(scan.hasNext()) {//acts like an iterator
s = scan.nextLine();
}
• Option 2: Buffered Reader
BufferedReader in = new BufferedReader(new
FileReader(”myfile.txt"));
s = in.readLine(); //returns null when EOF reached
while(s != null) {
s = in.readLine();
}
in.close(); //remember to CLOSE the file!
Tips
• Scanner must be imported from java.util
• File and Readers must b e imported from
java.io
• Must deal with IOException
– Us e try/catch for file operations or declare throws
IOException in method header
– public static void main(String[] args) throws IOException
{ … }
File Output (Text)
• FileWriter allows you to write to a file
• PrintWriter provides interface of
System.out
• Remember to import correct packages
and handle exceptions
PrintWriter out = new PrintWriter(new FileWriter(”myfile.txt"));
out.println(“String 1”);
out.println(“String 2”);
out.close(); //remember to CLOSE the file!
