"Java Development Series"--Collection use method

Objective

In Java, we provide some simple collections like C + + generics, List,set,map and so on. Here, a brief description of how these collection containers are used, and the custom ordering of complex object elements.

first look at the frame diagram of the collection:

Since collection also inherits the iterator and comparable interfaces, we can use iterator to iterate through the elements, or we can rewrite our own sorting by customizing the CompareTo function.

List

1  Packagetestcollection;2 3 Importjava.util.ArrayList;4 ImportJava.util.Iterator;5 Importjava.util.List;6 7  Public classtestlist {8      Public Static voidMain (string[] args) {9List List =NewArrayList ();TenList.add ("Test1"); OneList.add ("Test2"); AList.add ("Test3"); -          -System.out.println ("Out by for!"); the          for(Object o:list) { - System.out.println (o); -         } -          +System.out.println ("Out by iterator!"); -Iterator Iterator =list.iterator (); +          while(Iterator.hasnext ()) { AString element =(String) Iterator.next (); at System.out.println (element); -         } -     } -}

Run results

for! test1test2test3out by iterator! Test1test2test3

Set, if a duplicate element is encountered, does not add

1  Packagetestcollection;2 3 ImportJava.util.HashSet;4 ImportJava.util.Set;5 6  Public classTestset {7      Public Static voidMain (string[] args) {8Set set =NewHashSet ();//using set is generally used hashset, this will be faster9Set.add ("Test1");TenSet.add ("Test2"); One         if(Set.add ("Test2")){ ASystem.out.println ("Add Successful"); -}Else{ -System.out.println ("Add Failed"); the         } -     } -}

Run results

Add failed

Map

1  Packagetestcollection;2 3 ImportJava.util.HashMap;4 ImportJava.util.Map;5 ImportJava.util.Set;6 7  Public classTestMap {8      Public Static voidMain (string[] args) {9Map map =NewHashMap ();Ten          OneMap.put (1, "Test1"); AMap.put (2, "Test2"); -          -SYSTEM.OUT.PRINTLN ("size" +map.size ()); theSystem.out.println (Map.get (1)); -          -Set keys =Map.keyset (); -          for(Object key:keys) { + System.out.println (key); -         } +          AMap.Remove (2); atSYSTEM.OUT.PRINTLN ("size" +map.size ()); -     } -}

Run results

Size 2test11

Custom Sort Functions

Person class , inheriting comparable interface, overloading CompareTo function

1  Packagetestcollection;2 3  Public classPersonImplementscomparable{4     PrivateString name;5     Private intAge ;6      PublicString GetName () {7         returnname;8     }9      Public voidsetName (String name) {Ten          This. Name =name; One     } A      Public intGetage () { -         returnAge ; -     } the      Public voidSetage (intAge ) { -          This. Age =Age ; -     } -      PublicPerson (String name,intAge ) { +          This. Name =name; -          This. Age =Age ; +     } A @Override at      Public intCompareTo (Object person)throwsclasscastexception { -         if(! (PersoninstanceofPerson )) { -             Throw NewClassCastException ("A person perspected!"); -         } -         intAge =(person ). Getage (); -         return  This. age-Age ; in     } -}

Test class

1  Packagetestcollection;2 3 Importjava.util.Arrays;4 5  Public classtestcomparable {6      Public Static voidMain (string[] args) {7person[] Persons =NewPerson[4];8Persons[0] =NewPerson ("test1", 18);9PERSONS[1] =NewPerson ("test2", 20);TenPERSONS[2] =NewPerson ("test3", 15); OnePERSONS[3] =NewPerson ("test4", 19); A          -System.out.println ("Before sorting!"); -          the          for(person p:persons) { -System.out.println ("Name:" +p.getname () + "Age:" +p.getage ()); -         } -          +System.out.println ("After sorting!"); - arrays.sort (persons); +          for(person p:persons) { ASystem.out.println ("Name:" +p.getname () + "Age:" +p.getage ()); at         } -     } -}

Run results

Before sorting!  aftersorting!  20

"Java Development Series"--Collection use method