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| Beide Seiten der vorigen Revision Vorhergehende Überarbeitung Nächste Überarbeitung | Vorhergehende Überarbeitung | ||
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becki:linux:java [2010-04-30 14:18] becki |
becki:linux:java [2010-10-19 12:50] (aktuell) becki |
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| ====== Java == | ====== Java == | ||
| - | ===== Links == | + | ===== Related Pages == |
| - | [[sunkurs]] | [[comparison table]] | + | <pagelist> |
| + | * [[java plumbing]] | ||
| + | * [[java web programming]] | ||
| + | * [[apache click]] | ||
| + | * [[apache tomcat]] | ||
| + | * [[jrunscript]] | ||
| + | </pagelist> | ||
| ===== Java Versions and Compatibility == | ===== Java Versions and Compatibility == | ||
| Zeile 278: | Zeile 284: | ||
| String readLine() throws IOException | String readLine() throws IOException | ||
| </code> | </code> | ||
| + | |||
| + | ===== Collections == | ||
| + | ==== Overview == | ||
| + | |||
| + | [[javatut>reallybigindex.html#collections|Chapter in the Java tutorial]] | ||
| + | |||
| + | | //[[javaref>api/java/util/Collection.html|Collection]]// |||| //[[javaref>api/java/util/Map.html|Map]]// || | ||
| + | | //[[javaref>api/java/util/Set.html|Set]]// || //[[javaref>api/java/util/List.html|List]]// | //[[javaref>api/java/util/Queue.html|Queue]]// | || | ||
| + | | | //[[javaref>api/java/util/SortedSet.html|SortedSet]]// | | | | //[[javaref>api/java/util/SortedMap.html|SortedMap]]// | | ||
| + | | HashSet LinkedHashSet | TreeSet | LinkedList Vector ArrayList | LinkedList, PriorityQueue | HashTable LinkedHashMap HashMap | TreeMap | | ||
| + | |||
| + | ==== Implementations == | ||
| + | |||
| + | * [[javatut>collections/implementations/|Overview]] | ||
| + | * [[http://www.developer.com/java/article.php/3829891|Selecting the Best Java Collection Class for Your Application]] | ||
| + | * [[javatut>collections/implementations/map.html|General purpose map implementations]] | ||
| + | |||
| + | ==== Methods == | ||
| + | |||
| + | <code java> | ||
| + | // important methods of List: | ||
| + | boolean add(E e) | ||
| + | void add(int index, E element) | ||
| + | boolean contains(Object o) | ||
| + | E get(int index) | ||
| + | int indexOf(Object o) | ||
| + | Iterator<E> iterator() | ||
| + | E remove(int index) | ||
| + | boolean remove(Object o) // Removes the first occurrence | ||
| + | Object[] toArray() | ||
| + | <T> T[] toArray(T[] a) | ||
| + | |||
| + | // important methods of Map | ||
| + | boolean containsKey(Object key) | ||
| + | boolean containsValue(Object value) | ||
| + | V get(Object key) | ||
| + | Set<K> keySet() // Returns a set of the keys | ||
| + | V put(K key, V value) // there is no add! | ||
| + | V remove(Object key) | ||
| + | |||
| + | // important methods of Queue: | ||
| + | boolean offer(E o) // Inserts the specified element at the end; also add() possible | ||
| + | E peek() // Retrieves, but does not remove, | ||
| + | E poll() // Retrieves and removes from the beginning; remove() also possible | ||
| + | </code> | ||
| + | |||
| + | * Set: has no special order and no duplicates are permitted, not indexed; methods ar a subset of List (no index operations) | ||
| + | * List: ordered, duplicates are permitted, indexed | ||
| + | * Map does not implement the collection interface | ||
| + | * 'Sorted' is a subset of 'Ordered' | ||
| + | * Ordering: | ||
| + | * //Lists// are always ordered by index | ||
| + | * //Linked// collections are always ordered by insertion or last access | ||
| + | * //Tree// collections are always sorted | ||
| + | * List can made thread-save by Collections.synchronizedList() | ||
| + | * Tutorial: Vector is a legacy class; API: Vector is a normal class; Hashtable is similar; Vector also implements List | ||
| + | * HashSet & LinkedHashSet: Overwrite hashCode() so that equal objects provide the same hashcode | ||
| + | * LinkedList implements //List// and //Queue// | ||
| + | * //Queue// has Fifo (not stack) behaviour! | ||
| + | * All Interfaces have a size() method | ||
| + | * PriorityQueue sorts Elements by natural order using Comparable | ||
| + | * Elements for SortedSet/TreeSet, SortedMap/TreeMap | ||
| + | |||
| + | PriorityQueue must implement the Comparable interface! | ||
| + | * String implements interface Comparable<String> and Integer implements Comparable<Integer> -> Trying to add both Types to any untyped (old style) Tree-Container results in a ClassCastException | ||
| + | * Whereas adding only the same Type (eg Strings) works but gives a compiler warning. (I assume the type is detected at run time by reflection and the Object to compare is casted to String before compareTo() is called.) | ||
| + | |||
| + | ==== Sorting and Searching == | ||
| + | === Sorting with the Comparable Interface == | ||
| + | |||
| + | To sort a //List// (eg ArrayList) or an array use: | ||
| + | <code java> | ||
| + | static void Collections.sort(List<T> list); | ||
| + | static void Arrays.sort(allPrimitivesAndObject[] a); | ||
| + | </code> | ||
| + | The List interface has no sort method! All elements in the List or array must implement the Comparable interface: | ||
| + | |||
| + | <code java> | ||
| + | Interface Comparable<T> { | ||
| + | int compareTo(T o); | ||
| + | } | ||
| + | </code> | ||
| + | Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object. Keep in mind that compareTo accepts Type T (the generic of the List) wheras equals always only accepts type Object! | ||
| + | |||
| + | === Sorting with the Comparator Interface == | ||
| + | |||
| + | <code java> | ||
| + | static void Collections.sort(List<T> list, Comparator<? super T> c); | ||
| + | static void Arrays.sort(T[] a, Comparator<? super T> c); // T is an Object, no primitives! | ||
| + | |||
| + | Interface Comparator<T> { | ||
| + | int compare(T o1, T o2); | ||
| + | } | ||
| + | </code> | ||
| + | |||
| + | === Searching == | ||
| + | |||
| + | <code java> | ||
| + | static int Collections.binarySearch(List<T> list, T key[, Comparator<? super T> c]); | ||
| + | static int Arrays.binarySearch(allPrimitivesAndObject[] a, allPrimitivesAndObject key); | ||
| + | static int Arrays.binarySearch(T[] a, T key, Comparator<? super T> c); | ||
| + | </code> | ||
| + | Call binarySearch() with the array or List as first param, the key as second, and, if not all items implement the Comparable interface, provide a Comparator as 3rd parameter. List or array has to be sorted before binarySearch can be called, otherwise the result is not predictable! If the element is not found, binarySearch returns -length-1 | ||
| ===== Threads == | ===== Threads == | ||
| Zeile 697: | Zeile 806: | ||
| ===== Further Reading / 2do == | ===== Further Reading / 2do == | ||
| - | * [[Java Web Programming]] | + | * Intro to the [[ibm>java/library/j-5things9.html|Java Scripting API]] with [[jrunscript]] |
| * Doc general Java strategy: Use [[Apache Pivot]] for the GUI, [[JUnit]] for testing, [[Apache Ant]] for building, JWS for distribution and [[Groovy]] for coding | * Doc general Java strategy: Use [[Apache Pivot]] for the GUI, [[JUnit]] for testing, [[Apache Ant]] for building, JWS for distribution and [[Groovy]] for coding | ||
| * [[http://www.linux-magazin.de/Heft-Abo/Ausgaben/2008/08/Reiches-Angebot|Webentwicklung mit Java]]: An Overview (german) | * [[http://www.linux-magazin.de/Heft-Abo/Ausgaben/2008/08/Reiches-Angebot|Webentwicklung mit Java]]: An Overview (german) | ||
becki/linux/java.1272637099.txt.gz · Zuletzt geändert: 2010-04-30 14:18 von becki
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