enhanced for loop
String [] horsemen = {"war", "famine" , "pestilence", "death" }
for (String horsemen : horsemen )
System.out.println (horseman) ;
There is an
Iterator interface
Iterable interface
Iterator interface defines methods:
- boolean hasNext () : returns true if next() returns an element
- T next()
- boolean remove()
Scanner testScan = new Scanner (~)
while ( scan.hasNext() ) {
String token = testscan.next() ;
/* code to process token */
}but....
for (String token : testScan ) ! not legal
because Scanner doesn't implement Iterable
Iterable Specifies iterator ()
- iterator returns an object of type Iterator
ArrayList implements both Iterable, Iterator.
-------
ArrayList arrayListOfFoo = new ArrayList ();
for ( Foo refToFoo : arrayListofFoo {
/* do something * /
}compared to
ArrayList arrayListOfFoo = new ArrayList() ;
Iterator arrayListIter = arrayListOfFoo.iterator () ;
while (arrayListIter.hasNext() ) {
Foo refToFoo = arrayListIter.next() ;
/* Code to do something */
}Recall collections of MPs
-unorganised rabble (set)
linear order (list)
nonlinear order (Tree)
public void printlistofMPs ( collection all MPs )
{ for (MemberOfParliment one Mp: all MPs )
{ System.out.print;n(oneMP); }
}
Iterable
Iterator
* return an object of type Iterator
Iterator
boolean hasNext() return true iff a call to next() will return an object
T next() return the next object from the collectionl repeared calls to next() will return every element exactly once Order will depend on the type of collection.
void remove () remove the element
Collection
int size() return the number of things in the underlying collection
boolean add (E e) add a thing to the underlying collection
boolean remove (Object o) remove from the underlying collection to the first thing hat is equal to the object provided as a parameter
public interface List
void add (int index, E e) add an element at the specified position
E get (int index) Retrieve the element at the specified position
E remove (int index) Remove the element at the specified position.
