Recitation 1 CS0445 Data Structures Mehmud Abliz

Outline Discuss the following features of JAVA –Scanner (reading lines of input) –String Manipulation –Linked List –Hash Map

Scanner class A simple text scanner which can parse primitive types and strings. A Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace. The resulting tokens may then be converted into values of different types using the various next methods.

Example(1) this code allows a user to read a number from System.in. Scanner sc = new Scanner(System.in); int i = sc.nextInt();

Example(2) import java.io.File; import java.io.FileNotFoundException; import java.util.Scanner; public class TextScanner { private static void readFile(String fileName) { try { File file = new File(fileName); Scanner scanner = new Scanner(file); while (scanner.hasNext()) { System.out.println(scanner.next()); } scanner.close(); } catch (FileNotFoundException e) { e.printStackTrace(); }

Example(2) Cont. public static void main(String[] args) { if (args.length != 1) { System.err.println("usage: java TextScanner1" + "file location"); System.exit(0); } readFile(args[0]); }

String manipulation Some examples of string usage: System.out.println("abc"); String cde = "cde"; System.out.println("abc" + cde); String c = "abc".substring(2,3); String d = cde.substring(1, 2);

String manipulation functions length(): returns the length of this string. charAt() : returns the character at the specified index. An index ranges from 0 to length() - 1. indexOf(): returns the index of the first occurrence of the specified character within this string. substring(): returns a new string that is a substring of this string.

Linked List LinkedList class: –can be used as a stack, queue, or double- ended queue.

Linked List – some methods add(int, Object): inserts the specified element at the specified position in this list. add(Object): appends the specified element to the end of this list. contains(Object): returns true if this list contains the specified element. get(int): returns the element at the specified position in this list.

Linked List – some methods size(): returns the number of elements in this list. isEmpty(): returns true if this list contains no elements.

Example(3) class LinkedListExample { public static void main(String[] args) throws Exception { LinkedList list = new LinkedList(); list.add("Hello"); list.add("world"); list.add(0,"there"); list.add(0,"there1"); list.add(1,"here"); ListIterator itt = list.listIterator(); while (itt.hasNext()) { String line = (String) itt.next(); System.out.println(line); } } // end main }

HashMap HashMap is hash table based implementation of the Map interface. The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls. This class makes no guarantees as to the order of the map.

HashMap – Some methods put(Object, Object): associates the specified value with the specified key in this map. get(Object key): returns the value to which the specified key is mapped in this identity hash map, or null if the map contains no mapping for this key.

HashMap – Some methods containsKey(Object key): returns true if this map contains a mapping for the specified key. containsValue(Object value): returns true if this map maps one or more keys to the specified value.

HashMap – Some methods keySet(): returns a set view of the keys contained in this map. Returned object is a Set object, and can be usedconverted to an array with toArray(). values(): returns a collection view of the values contained in this map.

HashMap Example // Create a new HashMap HashMap hash = new HashMap(); // Add values to the created HashMap hash.put("one", new Integer(1)); hash.put("two", new Integer(2)); hash.put("three", new Integer(3));