Question

我一直在攻读SCJP，现在是Oracle认证专业Java SE程序员考试。

我很难将所有不同的收藏品包裹起来以及何时使用它们。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。我必须确定输出的输出方式以及每个集合的主要“功能”。

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，或者是否有任何遗漏。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。

所涵盖的藏品包括： 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?
    }
}

Answer 1

对于初学者，您应该refactor您的代码。基本上，无论你在哪里使用“复制粘贴”，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?
}

然后代替您拥有的方法，执行以下操作：

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

为你拥有的所有藏品做到这一点。

接下来，为您的地图做类似的事情：

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。

我可以让某人验证我的SCJP考试的收藏

1 个答案: