CS 110: Introduction to Computer Science Spring 2008 Java I/O Input: The Scanner class The scanner class is used to read in data from the end-user, providing functionality similar to Python’s input() and raw_input() methods. Example: import java.util.*; class ScannerDemo { public static void main(String[] args) { Scanner scanner = new Scanner(System.in); System.out.print("Enter a string:"); String s = scanner.next(); System.out.println(s); } } The specification for Scanner class can be found within the Java 1.5 API: http://java.sun.com/j2se/1.5.0/docs/api/index.html Scanner has nextX methods for each type: Java Python s =scanner.next() s = raw_input() i=scanner.nextInt() i = input() f=scanner.nextFloat() f = input() Consider the line: Scanner scanner = new Scanner(System.in); The parameter is a file. System.in is a system defined ‘file’ mapped to the keyboard. If you want to read from a file, you can just do something like the following: Scanner sc = new Scanner(new File("myNumbers")); The 'hasNext()' method can be used to see if at end of file: while (sc.hasNext()) { s = sc.next() }CS 110: Introduction to Computer Science Spring 2008 We’ll look at file I/O in more detail later. Output: System.out.println In Java, everything is object-oriented. So you can’t just call a 'print' function as in Python. Even printing requires an class, in this case a Java library class named System: Java Python System.out.print("hello world") print ("hello world") In Class Assignment: For your Person class, write a method named ‘readData’ that allows the user to enter the data (name, age) for a person. To test your method add code like the following to your main: Person ralph= new Person(); ralph.readData(); System.out.println(ralph.name);
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