Java Tutorial Lab 8

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LAB #8
Prepared by: Berk Soysal
2016 Winter

 Often, you will want to cycle through the elements in a
collection. For example, you might want to display each
element ...

Iterator ListIterator
Unidirectional (forward iteration)
Has only next()
Bidirectional (forward and backward iteration)
Ha...

 The Iterator interface specifies 3 methods:
boolean hasNext()
//returns true if this iteration has more elements
E next(...

Imagine a fence made up of fence posts
and rail sections.
fenceposts
rails
2016 Winter

 The iterator lives on the fence posts
 The data in the collection are the rails
 Iterator created at the far left post...

ArrayList<String> names =new ArrayList<String>();
names.add(“Alex”);
names.add(“Liz”);
names.add(“Tim”);
names.add(“Jack”)...

“Alex” “Liz” “Tim” “Jack”
while( it.hasNext() ) {
i++;
System.out.println( it.next() );
}
// when i == 1, prints out Alex
...

“Alex” “Liz” “Tim” “Jack”
while( it.hasNext() ) {
i++;
System.out.println( it.next() );
}
// when i == 2, prints out Liz
2...

“Alex” “Liz” “Tim” “Jack”
while( it.hasNext() ) {
i++;
System.out.println( it.next() );
}
// when i == 3, prints out Tim
2...

“Alex” “Liz” “Tim” “Jack”
while( it.hasNext() ) {
i++;
System.out.println( it.next() );
}
// when i == 4, prints out Jack
...

“Alex” “Liz” “Tim” “Jack”
while( it.hasNext() ) {
i++;
System.out.println( it.next() );
}
// while loop stops since call t...

 An Iterator can be used to remove things from the Collection
 Can only be called once per call to next()
public void re...

 In Java, just like methods, variables of a class too can
have another class as its member. Writing a class within
anothe...

 We know a regular class cannot be associated with the
access modifier private, but if we have the class as a
member of o...

You are provided an almost complete implementation of a
class. Complete the implementation of the class BitList.
public Bi...

Use the class called Iterative. Implement the methods below. Your
solutions must be iterative (i.e. uses iterators).
2016 ...

2016 Winter

2016 Winter

• Map: an unordered collection that associates a
collection of element values with a set of keys so
that elements they can...

public interface Map {
Object put(Object key, Object value);
Object get(Object key);
Object remove(Object key);
boolean co...

• Map is an interface; you can't say new Map()
• There are two implementations:
– java.util.HashMap is best for most purpo...

Map<String,String> m = new HashMap<String,String> ();
grades.put("Martin", "A");
grades.put("Nelson", "F");
grades.put(“Al...

public class Example {
public static void main(String[] args){
Map m = new HashMap();
m.put("Newton", new Integer(1642));
...

• public Object get(Object key)
– returns the value at the specified key, or null if the key is
not in the map (constant t...

• A map itself is not regarded as a collection
– Map does not implement Collection interface
– although, in theory, it cou...

• Map interface has no iterator method; you can’t get an
Iterator directly
• must first call either
– keySet() returns a S...

Java Tutorial Lab 8

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