Recitation 1 CS0445 Data Structures

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Recitation 1 CS0445 Data Structures

• Mehmud Abliz

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Outline

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

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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.

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Example(1)
Scanner sc new Scanner(System.in) int i
sc.nextInt()

• this code allows a user to read a number from
  System.in.

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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()
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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(args0)
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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)
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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.

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Linked List

• LinkedList class
• can be used as a stack, queue, or double-ended
  queue.

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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.

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Linked List some methods

• size() returns the number of elements in this
  list.
• isEmpty() returns true if this list contains no
  elements.

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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
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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.

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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.

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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.

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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.

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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))