- The Collection interfaces
- Duplicates
- Sortability
- The Collection interface
- The Set interface
- The List Interface
- The Queue Interface
- The SortedSet Interface
- The Map Interface
- The SortedMap Interface
The Collection interfaces
Collections a container for objects, Maps are container for key-value pairs. Three criteria specify the sort of container: - Sortability - Uniqueness / Duplicates - Order of elements
Duplicates
Duplicates are defines as objects returning true on the equals(E e )-method call. This can vary per implementation.
Sortability
Sortable elements need to implement the compareTo()-method or use a data type that has this method implemented ( the natural order of the type).
The Collection interface
The basic interface contains following methods:
public boolean add(e);
public boolean addAll(c);
public void clear();
public boolean contains(o);
public boolean containsAll(c);
public boolean equals(Object o);
public int hashCode();
public boolean isEmpty();
public Iterator<E> iterator()
public boolean remove(o);
public boolean removeAll(c)
public boolean retainAll(c)
public int size();
public Object[] toArray()
public <T> T[] toArray(T[] a)
The Set interface
Has all methods of Collection but different implementation of some. No duplicates are allowed. Can be used for mathematic operations as e.g. join two sets, combine two sets or compare two sets.
The List Interface
Represents data with a defined order. On top of methods of Collection, it has a lot of methods to access elements index-wise. But also the iterator allows to loop over all elements position-wise, making this interface a sequence-like ADT.
The Queue Interface
Has methods allowing implementations of the stack and queue ADT.
The SortedSet Interface
Elements of the SortedSet are sortable. If no parameter is specified the natural order (order of the datatype) is used. It is also possible to define your own Comparator class which implements the Comparator interface.
/**
Class ordering String-objects first on length, then on alphabetical value.
**/
static class LengthAlphaComparator implements Comparator<String> {
@Override
public int compare(String s1, String s2) {
if (s1.length() < s2.length()){
return -1;
}
if (s1.length() > s2.length()){
return 1;
}
return s1.compareTo(s2);
}
}
SortedSet<String> mySet = new TreeSet<>(new LengthAlphaComparitor());
The Map Interface
Most methods of this interface give access to objects by its key value.
The SortedMap Interface
In a SortedMap are the keys sortable. The keys are a SortedSet and can be iterated in the order specified by the Comparator class.
