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PriorityQueue<E> Class
Works with Comparable objects (or takes a
comparator as a parameter).
The smallest item has the highest priority.
Implements a priority queue as a min-heap
PriorityQueue
«interface»
Queue
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Java Collections: Stacks and Queues, Slides of Java Programming
An overview of stacks and queues in java collections framework. It explains their differences, use cases, implementations, and properties. The document also includes examples of using stacks for matching brackets and traversing a tree, and queues for finding matches in a file. It is useful for university students studying computer science or software engineering, particularly those focusing on data structures and algorithms.
Typology: Slides
2011/2012
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PriorityQueue< E > Class
Works with Comparable objects (or takes a
comparator as a parameter).
The smallest item has the highest priority.
Implements a priority queue as a min-heap
PriorityQueue
«interface» Queue
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push
pop
Stack Queue
LIFO (Last-In-First-Out) access method
add
remove
FIFO (First-In-First-Out) access method
Stacks and queues are used for temporary
storage, but in different situations
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Stack: Array Implementation
Stack pointer sp
myElements[5] myElements[4] myElements[3] value myElements[2] value myElements[1] value myElements[0] value
public void push (Object x) { myElements [sp] = x; sp++; }
public Object pop ( ) { sp--; return myElements [sp]; }
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ArrayList Implementation
import java.util.ArrayList;
public class ArrayStack { private ArrayList ;
public ArrayStack () { items = new ArrayList
public boolean isEmpty () { return items. isEmpty (); } public void push (Object x) { items. add (x); } public Object pop () { return items. remove (items. size () - 1); } public Object peek ( ) { return items. get (items. size () - 1); } }
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Properties of Stacks
In an efficient implementation, push, pop, and peek
methods run in O (1) time.
A stack of objects holds references to objects.
If necessary, a stack can hold multiple references to
the same object.
If you are not careful, an object can change while
stored on the stack (unless that object is immutable).
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java.util.Stack class
Part of the Java Collections Framework.
A ―generic‖ class (works with objects of
specified type).
Based on the legacy Vector class, similar to
ArrayList.
Methods: isEmpty, push, pop, peek.
Has other methods do not use them!
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Stack Example:Traversing a Tree Stack stk = new Stack
Save for future processing
if no children, take the next node from the stack
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Queues are used for:
Processing events or messages in order of their
arrival
System tasks
Queueing print jobs
Entering keystrokes
Processing mouse clicks
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Properties of Queues
In an efficient implementation, add, remove, and
peek methods run in O (1) time.
A queue of objects holds references to objects.
If necessary, a queue can hold multiple references
to the same object.
If you are not careful, an object can change while
stored in the queue (unless that object is immutable).
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The java.util.Queue Interface
A ―generic‖ interface, part of the Java
Collections Framework
Implemented by java.util.LinkedList
boolean isEmpty () boolean add (E obj) E remove () E peek ()
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Sets
A set is a collection without duplicate values
What is a ―duplicate‖ depends on the
implementation
Designed for finding a value quickly
java.util:
Set interface
TreeSet
HashSet
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Sets (cont‘d)
«interface» Collection
«interface» Iterator
TreeSet HashSet
«interface» Set Methods of Set < E > are the same as methods of Collection < E >
Set ‟s semantics are different from Collection (no duplicates), but Set does not add any new methods.
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HashSet< E >
Works with objects for which reasonable
hashCode and equals methods are defined
Implements a set as a hash table
contains, add, and remove methods run in O (1)
time
Iterator returns elements in no particular order
TreeSet HashSet
«interface» Set
Example
import java.util.*; public class SetExample { public static void main(String args[]) { Set set = new HashSet(); set.add("Bernadine"); set.add("Elizabeth"); set.add("Gene"); set.add("Elizabeth"); set.add("Clara"); System.out.println(set); Set sortedSet = new TreeSet(set); System.out.println(sortedSet); } } adrish.b@ardentcollaboratio
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