Transcript CS0445 Data Structures Recitation 1

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