我一直在学习SCJP,现在是Oracle认证专业Java SE程序员考试 .
我很困难地把头缠在所有不同的收藏品上以及什么时候使用它们 . 我也喜欢闪存卡 . 所以我尝试创建一组基本相同的类,除了他们正在使用的集合 . 我将不得不确定输出将如何产生以及每个集合的主要“特征”是什么 .
不幸的是我不相信自己 . 我想让某人确认所有信息都是准确的,或者是否有遗漏 . 然后经过一些反馈/更正之后,我认为对于其他试图理解Java集合的人来说,这将是一个很好的练习 .
涵盖的集合包括:HashMap,Hashtable,TreeMap,LinkedHashMap,HashSet,TreeSet,LinkedHashSet,ArrayList,Vector,LinkedList,PriorityQueue .
我也将所有文件分开,可以在这里下载:http://www.allgo.com/personal/MyCollections.zip
提前致谢
import java.util.*;
import java.lang.*;
class MyItem implements Comparable{
private String name;
MyItem(String n){ name = n; }
public String toString(){return name;}
public String getName(){return name;}
public boolean equals(Object obj){
if(this==obj) return true;
else if(obj==null) return false;
else if(getName() != ((MyItem)obj).getName()) return false;
else return true;
}
public int hashCode(){ return 5; }
public int compareTo(MyItem b){return b.getName().compareTo(getName());}
}
public class MyCollections{
public static void main(String[] args){
MyHashMap.main(args); System.out.println("HashMap: Hash=Unsorted, Unordered. Map=key/value pair\n##\n");
MyHashtable.main(args); System.out.println("Hashtable: Thread Safe. Hash=Unsorted, Unordered. Map=key/value pair\n##\n");
MyTreeMap.main(args); System.out.println("TreeMap: Tree=sorted. Map=key/value.\n##\n");
MyLinkedHashMap.main(args); System.out.println("LinkedHashMap: Linked=Maintains Insertion Order. Hash=unsorted, unordered. Map=key/value pair.\n##\n");
MyHashSet.main(args); System.out.println("HashSet: Hash=Unsorted, Unordered. Set=Unique. Define=equals/hashCode\n##\n");
MyTreeSet.main(args); System.out.println("TreeSet: Tree=Sorted. Set=Unique. Define=Comparable/Comparator\n##\n");
MyLinkedHashSet.main(args); System.out.println("LinkedHashSet: Liniked=Maintains Insertion Order. Hash=Unsorted. Set=Unique. Define=equals/hashCode\n##\n");
MyArrayList.main(args); System.out.println("ArrayList: List=Queue. Maintains insertion order, Allowed duplicates\n##\n");
MyVector.main(args); System.out.println("Vector: Thread Safe. ArrayList. Maintains Insertion Order, Allows duplicates\n##\n");
MyLinkedList.main(args); System.out.println("LinkedList: Linked=Maintaines Insertion Order. List=Queue. Advanced ArrayList with more methods.\n##\n");
MyPriorityQueue.main(args); System.out.println("PriorityQueue: Define=Comparable/comparator\n##\n");
}
}
class MyHashMap{
public static void main(String[] args){
HashMap c = new HashMap();
MyItem Eight = new MyItem("Eight");
c.put(5, new MyItem("Five")); c.put(1, new MyItem("One")); c.put(8, Eight); c.put(3, new MyItem("Three"));
c.put(4, new MyItem("Four")); c.put(1, new MyItem("1")); c.put(8, Eight); c.put(9, new MyItem("Nine"));
c.remove(3); c.put(7, new MyItem("Seven"));
System.out.println(c);//output?
}
}
class MyHashtable{
public static void main(String[] args){
Hashtable c = new Hashtable();
MyItem Eight = new MyItem("Eight");
c.put(5, new MyItem("Five")); c.put(1, new MyItem("One")); c.put(8, Eight); c.put(3, new MyItem("Three"));
c.put(4, new MyItem("Four")); c.put(1, new MyItem("1")); c.put(8, Eight); c.put(9, new MyItem("Nine"));
c.remove(3); c.put(7, new MyItem("Seven"));
System.out.println(c);//output?
}
}
class MyTreeMap{
public static void main(String[] args){
TreeMap c = new TreeMap();
MyItem Eight = new MyItem("Eight");
c.put(5, new MyItem("Five")); c.put(1, new MyItem("One")); c.put(8, Eight); c.put(3, new MyItem("Three"));
c.put(4, new MyItem("Four")); c.put(1, new MyItem("1")); c.put(8, Eight); c.put(9, new MyItem("Nine"));
c.remove(3); c.put(7, new MyItem("Seven"));
System.out.println(c);//output?
}
}
class MyLinkedHashMap{
public static void main(String[] args){
LinkedHashMap c = new LinkedHashMap();
MyItem Eight = new MyItem("Eight");
c.put(5, new MyItem("Five")); c.put(1, new MyItem("One")); c.put(8, Eight); c.put(3, new MyItem("Three"));
c.put(4, new MyItem("Four")); c.put(1, new MyItem("1")); c.put(8, Eight); c.put(9, new MyItem("Nine"));
c.remove(3); c.put(7, new MyItem("Seven"));
System.out.println(c);//output?
}
}
class MyHashSet{
public static void main(String[] args){
HashSet c = new HashSet();
MyItem Eight = new MyItem("Eight");
c.add(new MyItem("Five")); c.add(new MyItem("One")); c.add(Eight); c.add(new MyItem("Three"));
c.add(new MyItem("Four")); c.add(new MyItem("One")); c.add(Eight); c.add(new MyItem("Nine"));
c.remove(3); c.add(new MyItem("Seven"));
System.out.println(c);//output?
}
}
class MyTreeSet{
public static void main(String[] args){
TreeSet c = new TreeSet();
MyItem Eight = new MyItem("Eight");
c.add(new MyItem("Five")); c.add(new MyItem("One")); c.add(Eight); c.add(new MyItem("Three"));
c.add(new MyItem("Four")); c.add(new MyItem("One")); c.add(Eight); c.add(new MyItem("Nine"));
c.remove(Eight); c.add(new MyItem("Seven"));
System.out.println(c);//output?
}
}
class MyLinkedHashSet{
public static void main(String[] args){
LinkedHashSet c = new LinkedHashSet();
MyItem Eight = new MyItem("Eight");
c.add(new MyItem("Five")); c.add(new MyItem("One")); c.add(Eight); c.add(new MyItem("Three"));
c.add(new MyItem("Four")); c.add(new MyItem("One")); c.add(Eight); c.add(new MyItem("Nine"));
c.remove(3); c.add(new MyItem("Seven"));
System.out.println(c);//output?
}
}
class MyArrayList{
public static void main(String[] args){
ArrayList c = new ArrayList();
MyItem Eight = new MyItem("Eight");
c.add(new MyItem("Five")); c.add(new MyItem("One")); c.add(Eight); c.add(new MyItem("Three"));
c.add(new MyItem("Four")); c.add(new MyItem("One")); c.add(Eight); c.add(new MyItem("Nine"));
c.remove(3); c.add(new MyItem("Seven"));
System.out.println(c);//output?
}
}
class MyVector{
public static void main(String[] args){
Vector c = new Vector();
MyItem Eight = new MyItem("Eight");
c.add(new MyItem("Five")); c.add(new MyItem("One")); c.add(Eight); c.add(new MyItem("Three"));
c.add(new MyItem("Four")); c.add(new MyItem("One")); c.add(Eight); c.add(new MyItem("Nine"));
c.remove(3); c.add(new MyItem("Seven"));
System.out.println(c);//output?
}
}
class MyLinkedList{
public static void main(String[] args){
LinkedList c = new LinkedList();
MyItem Eight = new MyItem("Eight");
c.add(new MyItem("Five")); c.add(new MyItem("One")); c.add(Eight); c.add(new MyItem("Three"));
c.add(new MyItem("Four")); c.add(new MyItem("One")); c.add(Eight); c.add(new MyItem("Nine"));
c.remove(3); c.add(new MyItem("Seven"));
System.out.println(c);//output?
}
}
class MyPriorityQueue{
public static void main(String[] args){
PriorityQueue c = new PriorityQueue();
MyItem Eight = new MyItem("Eight");
c.offer(new MyItem("Five")); c.offer(new MyItem("One")); c.offer(Eight); c.offer(new MyItem("Three"));
c.offer(new MyItem("Four")); c.offer(new MyItem("One")); c.offer(Eight); c.offer(new MyItem("Nine"));
System.out.println(c.peek());
System.out.println(c.poll());
c.offer(new MyItem("Seven"));
System.out.println(c);//output?
}
}
1 回答
对于初学者,你应该refactor你的代码 . 基本上,无论你在哪里使用"copy paste",都不要 .
创建一个这样的方法:
然后,而不是你拥有的方法,执行以下操作:
并为您拥有的所有藏品做到这一点 .
接下来,为您的 Map 做类似的事情:
您的代码将缩小,可读,甚至可能有一天变得可用 .