当要大量使用key来查找value的时候,HashTable无疑是最有选择,HashTable与ArrayList一样,是非泛型的,value存进去是object,存取会发生装箱、拆箱,所以出现了Dictionary<T,T>。 Dictionary<T,T>是HashTable的泛型版本,存取同样快,但是不需要装箱和拆箱了。而且,其优化了算法,Hashtable是0.72,它的浪费容量少了很多。 Di...
import java.util.*; public class ReflectTest2 { public static void main(String[]args) { //面向父类的编程或者面向接口编程 Collection c1=new HashSet() ; MyTest t1=new MyTest(2,2) ; MyTest t2=new MyTest(3,4) ; MyTest t3=new MyTest(2,2) ; c1.add(t1) ; c1.add(t2) ; c1.a...
"Manager"));6org.add(newEmployee("Tim", "Developer"));7org.add(newEmployee("Frank", "Developer"));89//Collection<Employee> copy = new HashSet<>(org);10Collection<Employee> copy =newHashSet<Employee>(org.size());111213System
1,用HashSet存储字符串并遍历 package com.heima.set; import java.util.HashSet; public class Demo_1Hashset { /* * set集合,无索引,不可以重复,无序(存取不一致) */ public static void main(String[] args) { // TODO Auto-generated method stub HashSet<String> hs = new HashSet<>(); //创...
ArrayList与Vector初始化容量一样，为10；HashSet、HashMap初始化容量一样，为16；而HashTable独独使用11，又是一个很有意思的问题。小结 有很多问题是没有明确原因、明确的答案的。就好像一个女孩儿对你没感觉，可能是因为你不够好，也可能是她已经爱上别人了，但也有很大可能你是不会知道答案。但在寻找原因和...
= HashSet<>(Arrays.asList("a","b","c","d","e","f")); Iterator<String> it = stringsToSearch.iterator();while(it.hasNext()) {if(matchingStrings.contains(it.next())) { it.remove(); } }Copy 7. Summary In this quick article, we had a look at the ArrayList in Java. ...
Contains(1, 6) // false _ = set.Values() // []int{1,5} (in order) set.Clear() // empty set.Empty() // true set.Size() // 0 } LinkedHashSet A set that preserves insertion-order. Data structure is backed by a hash table to store values and doubly-linked list to store ...
{Map<Integer,String>map1=newHashMap<Integer,String>();//Map/HashMap都可以map1.put(100,"aa");map1.put(200,"bb");map1.put(300,"cc");//iterator第一种遍历map的方式(键值对)System.out.println("iterator第一种遍历map的方式");Set<Entry<Integer,String>>ss=map1.entrySet();//Map.Entry/...
创建时直接添加元素 实现了collection接口的类ArrayList<String>list1=newArrayList<>(list);System.out.println(Arrays.toString(list1.toArray()));HashSet<String>hashSet=newHashSet<>();hashSet.add("C");ArrayList<String>list2=newArrayList<>(hashSet);System.out.println(Arrays.toString(list2.toArray(...
// c.toArray might (incorrectly) not return Object[] (see 6260652) ① if (elementData.getClass() != Object[].class) elementData = Arrays.copyOf(elementData, size, Object[].class); } else { // replace with empty array. this.elementData = EMPTY_ELEMENTDATA; ...