1、容器的打印
import java.util.ArrayList; import java.util.Arrays; import java.util.Collection; import java.util.HashMap; import java.util.HashSet; import java.util.LinkedHashMap; import java.util.LinkedHashSet; import java.util.LinkedList; import java.util.List; import java.util.Map; import java.util.TreeMap; import java.util.TreeSet; public class Tree1 { static Collection fill(Collection<String> collection) { collection.add("rat"); collection.add("cat"); collection.add("dog"); collection.add("dog"); return collection; } static Map fill(Map<String,String> map) { map.put("rat", "Fuzzy"); map.put("cat", "Rags"); map.put("dog", "Bosco"); map.put("dog", "Spot"); return map; } public static void main (String[] args) { System.out.println(fill(new ArrayList<String>())); System.out.println(fill(new LinkedList<String>())); System.out.println(fill(new HashSet<String>())); System.out.println(fill(new TreeSet<String>())); System.out.println(fill(new LinkedHashSet<String>())); System.out.println(fill(new HashMap<String,String>())); System.out.println(fill(new TreeMap<String,String>())); System.out.println(fill(new LinkedHashMap<String,String>())); } }
输出是:
[rat, cat, dog, dog] [rat, cat, dog, dog] [rat, cat, dog] [cat, dog, rat] [rat, cat, dog] {rat=Fuzzy, cat=Rags, dog=Spot} {cat=Rags, dog=Spot, rat=Fuzzy} {rat=Fuzzy, cat=Rags, dog=Spot}
输出证明:
a、前五个是Collection打印出来的内容是用方括号括住的,Map则由大括号括住。
b、Collection在每个槽只能保存一个元素,Set的元素不能重复
c、HashSet、TreeSet、LinkedHashSet三者的区别就是顺序,这是因为存储元素的方式不同,HashSet采用很复杂的方式存储元素,TreeSet通过比较结果的升序保存对象,LinkedHashSet按照被添加的顺序保存对象
d、HashMap、TreeMap、LinkedHashMap三者的区别同样是顺序,HashMap没有什么明显的顺序,TreeMap比较结果的升序保存键,LinkedHashMap按照插入的顺序。
2、PriorityQueue
按照自然顺序进行弹出的队列
import java.util.*; public class Tree1 { static void print(Queue queue) { while(queue.peek() != null) { System.out.print(queue.remove() + " "); } System.out.println(); } public static void main (String[] args) { List<Integer> ints = Arrays.asList(1,2,3,5,9,8,4,3,8,2,89,5,8,5,8); PriorityQueue<Integer> preiorityQueue = new PriorityQueue<Integer>(ints); print(preiorityQueue); preiorityQueue = new PriorityQueue<Integer>(ints.size(),Collections.reverseOrder()); preiorityQueue.addAll(ints); print(preiorityQueue); String stringPq = "what do you want to do"; List<String> stringPqs = Arrays.asList(stringPq.split("")); PriorityQueue<String> stringPQ = new PriorityQueue<String>(stringPqs); print(stringPQ); stringPQ = new PriorityQueue<String>(stringPqs.size(),Collections.reverseOrder()); stringPQ.addAll(stringPqs); print(stringPQ); } }
输出:
1 2 2 3 3 4 5 5 5 8 8 8 8 9 89
89 9 8 8 8 8 5 5 5 4 3 3 2 2 1
a a d d h n o o o o t t t u w w y
y w w u t t t o o o o n h d d a a
Integer的优先级是按照大小排列的,String中空格的优先级高于字母的