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-end

ed 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));