Java collection

JAVA
Collection classes
Prepared by
Miss. Arati A. Gadgil

Collections
•Collection represents a single unit of objects i.e. a group
•java.util package contains all the classes and interfaces for
Collection framework.
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Methods
public boolean add(Object element)
is used to insert an element in this collection.
public boolean addAll(collection c)
is used to insert the specified collection elements in the
invoking collection.
public boolean remove(Object element)
is used to delete an element from this collection.
public boolean removeAll(Collection c)
is used to delete all the elements of specified collection
from the invoking collection.
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public boolean retainAll(Collection c)
is used to delete all the elements of invoking collection except
the specified collection
public int size()
return the total number of elements in the collection.
public void clear()
removes the total no of element from the collection.
public boolean contains(object element)
is used to search an element.
public boolean containsAll(Collection c)
is used to search the specified collection in this collection 5

public Iterator iterator()
returns an iterator.
public Object[] toArray()
converts collection into array.
public boolean isEmpty()
checks if collection is empty.
public boolean equals(Object element)
matches two collection
public int hashCode()
returns the hashcode number for collection.
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Iterator interface
Iterator interface provides the facility of iterating the elements
in forward direction only.
Methods
1.public boolean hasNext()
it returns true if iterator has more elements.
2.public object next()
it returns the element and moves the cursor pointer to the
next element.
3.public void remove()
it removes the last elements returned by the iterator. It is
rarely used.

Java ArrayList class
Java ArrayList class uses a dynamic array for storing the elements.It
extends AbstractList class and implements List interface.
Java ArrayList class can contain duplicate elements.
Java ArrayList class maintains insertion order.
Java ArrayList class is non synchronized.
Java ArrayList allows random access because array works at the index
basis.
In Java ArrayList class, manipulation is slow because a lot of shifting
needs to be occurred if any element is removed from the array list.
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Java LinkedList class
Java LinkedList class uses doubly linked list to store the elements. It
extends the AbstractList class and implements List and Deque interfaces.
Java LinkedList class can contain duplicate elements.
Java LinkedList class maintains insertion order.
Java LinkedList class is non synchronized.
In Java LinkedList class, manipulation is fast because no shifting needs
to be occurred.
Java LinkedList class can be used as list, stack or queue
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Difference between ArrayList and LinkedList
ArrayList LinkedList
1) ArrayList internally uses dynamic
array to store the elements.
LinkedList internally uses doubly linked
list to store the elements.
2) Manipulation with ArrayList
is slow because it internally uses array. If
any element is removed from the array,
all the bits are shifted in memory.
Manipulation with LinkedList
is faster than ArrayList because it uses
doubly linked list so no bit shifting is
required in memory.
3) ArrayList class can act as a list only
because it implements List only.
LinkedList class can act as a list and
queue both because it implements List
and Deque interfaces.
4) ArrayList is better for storing and
accessing data.
LinkedList is better for
manipulating data.
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Java List Interface
List Interface is the subinterface of Collection.It contains methods to
insert and delete elements in index basis.It is a factory of ListIterator
interface.
Commonly used methods of List Interface:
public void add(int index,Object element);
public boolean addAll(int index,Collection c);
public object get(int Index position);
public object set(int index,Object element);
public object remove(int index);
public ListIterator listIterator();
public ListIterator listIterator(int i);
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Java ListIterator Interface
ListIterator Interface is used to traverse the element in backward and
forward direction.
Commonly used methods of ListIterator Interface:
public boolean hasNext();
public Object next();
public boolean hasPrevious();
public Object previous();
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Difference between List and Set
List can contain duplicate elements whereas Set contains unique
elements only.
Java HashSet class
uses hash table to store the elements. It extends AbstractSet class and
implements Set interface.
contains unique elements only
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Java Queue Interface
Methods of Queue Interface
public boolean add(object);
public boolean offer(object);
public remove();
public poll();
public element();
public peek();
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Java Map Interface
A map contains values based on the key i.e. key and value pair.Each
pair is known as an entry.Map contains only unique elements.
Commonly used methods of Map interface:
public Object put(object key,Object value):
is used to insert an entry in this map.
public void putAll(Map map)
is used to insert the specified map in this map.
public Object remove(object key)
is used to delete an entry for the specified key.
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public Object get(Object key)
is used to return the value for the specified key.
public boolean containsKey(Object key)
is used to search the specified key from this map.
public boolean containsValue(Object value)
is used to search the specified value from this map.
public Set keySet()
returns the Set view containing all the keys.
public Set entrySet()
returns the Set view containing all the keys and values.
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Entry
Entry is the subinterface of Map.So we will access it by Map.Entry
name.It provides methods to get key and value.
Methods of Entry interface:
public Object getKey()
is used to obtain key.
public Object getValue()
is used to obtain value
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Sorting
We can sort the elements of:
String objects
Wrapper class objects
User-defined class objects
Method
public void sort(List list)
is used to sort the elements of List.List elements must be of
Comparable type.
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Java Collections Framework
The Java Collections Framework is a collection of interfaces and classes
which helps in storing and processing the data efficiently. This
framework has several useful classes which have tons of useful functions
which makes a programmer task super easy.

Java collection

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