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我可以让某人验证我的SCJP考试的收藏

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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

  • 3

    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:

    private static void fill(Collection c) {
        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?
    }
    

    然后,而不是你拥有的方法,执行以下操作:

    class MyVector{
        public static void main(String[] args){
            Vector c = new Vector();
            fill(c);
        }
    }
    

    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:

    private static void fill(Map<?,?> map) {
        MyItem Eight = new MyItem("Eight");
        map.put(5, new MyItem("Five")); map.put(1, new MyItem("One")); map.put(8, Eight); map.put(3, new MyItem("Three"));
        map.put(4, new MyItem("Four")); map.put(1, new MyItem("1")); map.put(8, Eight); map.put(9, new MyItem("Nine"));
        map.remove(3); map.put(7, new MyItem("Seven"));
        System.out.println(map);//output?
    }
    

    您的代码将缩小,可读,甚至可能有一天变得可用 .

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