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Java class 5
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18-Oct-2014 -
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Transcript of Java class 5
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Input And Output
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Input and Output
• Input is the data what we give to the program.• Output is the data what we receive from the
program in the form of result.• Stream represents flow of data i.e. sequence of
data.• To give input we use InputStream and to
receive output we use OutputStream.
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How input is read from Keyboard?
System.in InputStreamReader BufferedReader
It represents keyboard. To read data from keyboard it should be connected to InputStreamReader
It reads data from keyboard and send that data to BufferedReader.
It reads data from InputStreamReader and stores data in buffer. It has got methods so that data can be easily accessed.
connected to send data to
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Reading Input from console
• Input can be given either from file or keyword.
• Input can be read from console in 3 ways.BufferedReaderStringTokenizerScanner
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BufferedReader
BufferedReader bufferedreader = new BufferedReader(new InputStreamReader(System.in));
int age = bufferedreader.read();String name = bufferedreader.readLine(); Methods
int read()String readLine()
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StringTokenizer
•It can be used to accept multiple inputs from console in a single line where as BufferedReader accepts only one input from a line.•It uses delimiter(space, comma) to make the input into tokens.
BufferedReader bufferedreader = new BufferedReader(newInputStreamReader(System.in));
String input = bufferedreader.readLine();
StringTokenizer tokenizer = new StringTokenizer(input, ”,”);String name = tokenizer.nextToken();int age=tokenizer.nextToken(); delimiter
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Scanner
• It accepts multiple inputs from file or keyboard and divides into tokens.
• It has methods to different types of input( int, float, string, long, double, byte) where tokenizer does not have.
Scanner scanner = new Scanner(System.in); int rollno = scanner.nextInt();` String name = scanner.next();
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Writing output to console
• The output can be written to console in 2 ways: print(String)-
System.out.print(“hello”); write(int)-
int input=‘i’;System.out.write(input);System.out.write(‘/n’);
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I/O StreamsI/O Streams
Byte Oriented Streams Unicode Character Oriented Streams
InputStream OutputStream Reader Writer
FileInputStreamDataInputStream
FileOutputStreamDataOutputStream
InputStreamReader
OutputStreamWriter
FileWriterFileReaderMay be buffered or unbuffered
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Array List
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ArrayList class
• The ArrayList class is a concrete implementation of the List interface.
• Allows duplicate elements.• A list can grow or shrink dynamically • On the other hand array is fixed once it is created.
– If your application does not require insertion or deletion of elements, the most efficient data structure is the array
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ArrayList class
Java.util.ArrayList size: 5
0 1 2 3 4 … …
Ravi Rajiv Megha Sunny Atif
elementData
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Java Programming: OOP 13
Methods in ArrayList
• boolean add(Object e)• void add(int index, Object
element)• boolean addAll(Collection c)
• Object get(int index)• Object set(int index,Object
element)
• Object remove(int index)
• Iterator iterator()• ListIterator listIterator()
• int indexOf()• int lastIndexOf()
• int index(Object element)• int size()• void clear()
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ArrayList - Insertion
// Create an arraylistArrayList arraylist = new ArrayList();
// Adding elementsarraylist.add("Rose");arraylist.add("Lilly");arraylist.add("Jasmine");arraylist.add("Rose");
//removes element at index 2arraylist.remove(2);
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Java Programming: OOP 15
How to trace the elements of ArrayList?
• For-each loop• Iterator• ListIterator• Enumeration
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Java Programming: OOP 16
For-each loop
• It’s action similar to for loop. It traces through all the elements of array or arraylist.
• No need to mention size of Arraylist.• for ( String s : arraylist_name)
Keyword type of data name of arraylist stored in arraylist
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Java Programming: OOP 17
Iterator
• Iterator is an interface that is used to traverse through the elements of collection.
• It traverses only in forward direction with the help of methods.
• boolean hasNext()• element next()• void remove ()
Iterator Methods
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Displaying Items using Iterator
Iterator iterator = arraylist.iterator();
while (iterator.hasNext()) {Object object = iterator.next();System.out.print(object + " ");
}
Java Programming: OOP
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Java Programming: OOP 19
ListIterator
• ListIterator is an interface that traverses through the elements of the collection.
• It traverses in both forward and reverse direction.
• boolean hasNext()• element next()• void remove ()• boolean
hasPrevious()• element previous()
ListIterator Methods
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Displaying Items using ListIterator
// To modify objects we use ListIteratorListIterator listiterator = arraylist.listIterator();
while (listiterator.hasNext()) {Object object = listiterator.next();listiterator.set("(" + object + ")");
}
Java Programming: OOP
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Java Programming: OOP 21
Enumeration
• Enumeration is an interface whose action is similar to iterator.
• But the difference is that it have no method for deleting an element of arraylist.
• boolean hasMoreElement()
• element nextElement()
Enumeration Methods
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Displaying Items using Enumeration
Enumeration enumeration = Collections.enumeration(arraylist);
while (enumeration.hasMoreElements()) {Object object =
enumeration.nextElement();System.out.print(object + " ");
}Java Programming: OOP
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HashMaps
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HashMap Class• The HashMap is a class which is used to perform operations such as
inserting, deleting, and locating elements in a Map . • The Map is an interface maps keys to the elements.• Maps are unsorted and unordered.• Map allows one null key and multiple null values• HashMap < K, V >
key value associated with key• key act as indexes and can be any objects.
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Java Programming: OOP 25
Methods in HashMap
• Object put(Object key, Object value)
• Enumeration keys()• Enumeration elements()• Object get(Object keys)
• boolean containsKey(Object key)• boolean containsValue(Object key)
• Object remove(Object key)• int size()• String toString()
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HashMap
01234...…
100
Ravi
Megha
Atif
Rajiv
Sunny
…..
………..
……….…….
Key Value
HashMap Class
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HashMap - Insertion
// Create a hash mapHashMap hashmap = new HashMap();
// Putting elementshashmap.put("Ankita", 9634.58);hashmap.put("Vishal", 1283.48);hashmap.put("Gurinder", 1478.10);hashmap.put("Krishna", 199.11);
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HashMap - Display
// Get an iteratorIterator iterator = hashmap.entrySet().iterator();
// Display elementswhile (iterator.hasNext()) {
Map.Entry entry = (Map.Entry) iterator.next();System.out.print(entry.getKey() + ": ");System.out.println(entry.getValue());
}
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Hashtable
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Hashtable Class
• Hashtable is a class which is used to perform operations such as inserting, deleting, and locating elements similar to HashMap .
• Similar to HashMap it also have key and value.• It does not allow null keys and null values.• The only difference between them is Hashtable
is synchronized where as HashMap is not by default.
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Java Programming: OOP 31
Methods in Hashtable
• Object put(Object key, Object value)
• Enumeration keys()• Enumeration elements()• Object get(Object keys)
• boolean containsKey(Object key)• boolean containsValue(Object key)
• Object remove(Object key)• int size()• String toString()
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Hashtable - Insertion
// Create a hash mapHashtable hashtable = new Hashtable();
// Putting elementshashtable.put("Ankita", 9634.58);hashtable.put("Vishal", 1283.48);hashtable.put("Gurinder", 1478.10);hashtable.put("Krishna", 199.11);
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Hashtable - Display
// Using EnumerationEnumeration enumeration = hashtable.keys();
// Display elementswhile (enumeration.hasMoreElements()) {
String key = enumeration.nextElement().toString();
String value = hashtable.get(key).toString();
System.out.println(key + ":"+value);}
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•Q& A..?
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Thanks..!