Java part 2

Java - Interfaces

Reference type
Collection of methods
Contains only behaviour of object not attributes
Countless methods
.java .class files similar to Class
Follows package flow
Cannot be instantiated
No constructors
Abstract methods
No instance fields
Class implements it. not extends
Can extend multiple Instances

Java - Collections

What is Collection?

A group of objects collected in single unit
Provides readymade architecture.
Represents a set of classes and interfaces.
optional.
Has Interfaces and its implementations, i.e., classes
Has Algorithms

Java - Collections

No.	Method	Description
1	public boolean add(E e)	It is used to insert an element in this collection.
2	public boolean addAll(Collection<? extends E> c)	It is used to insert the specified collection elements in the invoking collection.
3	public boolean remove(Object element)	It is used to delete an element from the collection.
4	public boolean removeAll(Collection<?> c)	It is used to delete all the elements of the specified collection from the invoking collection.
5	default boolean removeIf(Predicate<? super E> filter)	It is used to delete all the elements of the collection that satisfy the specified predicate.
6	public boolean retainAll(Collection<?> c)	It is used to delete all the elements of invoking collection except the specified collection.
7	public int size()	It returns the total number of elements in the collection.
8	public void clear()	It removes the total number of elements from the collection.
9	public boolean contains(Object element)	It is used to search an element.
10	public boolean containsAll(Collection<?> c)	It is used to search the specified collection in the collection.
11	public Iterator iterator()	It returns an iterator.
12	public Object[] toArray()	It converts collection into array.
13	public <T> T[] toArray(T[] a)	It converts collection into array. Here, the runtime type of the returned array is that of the specified array.
14	public boolean isEmpty()	It checks if collection is empty.
15	default Stream<E> parallelStream()	It returns a possibly parallel Stream with the collection as its source.
16	default Stream<E> stream()	It returns a sequential Stream with the collection as its source.
17	default Spliterator<E> spliterator()	It generates a Spliterator over the specified elements in the collection.

Java - Generics

List list = new ArrayList();

list.add(new Integer(2));
list.add("a String");

Integer integer = (Integer) list.get(0);

String string   = (String) list.get(1);

List<String> strings = new ArrayList<String>();

strings.add("a String");

String aString = strings.get(0);

List<String> strings = new ArrayList<String>();

//... add String instances to the strings list

for(String aString : strings)
  System.out.println(aString);