集合的特点

不存放重复的元素

常用于去重

• 存放新增 IP，统计新增 IP 量
• 存放词汇，统计词汇量
  ...

接口设计

package com.njf;

public interface Set<E> {
    int size();
    boolean isEmpty();
    void clear();
    boolean contains(E element);
    void add(E element);
    void remove(E element);
    /*
     * 遍历
     */
    void traversal(Visitor<E> visitor);
    /*
     * 抽象类
     */
    public static abstract class Visitor<E> {
        boolean stop;
        public abstract boolean visit(E element);
    }
}

集合的内部实现可以直接利用前面章节提到的数据结构

动态数组，链表，二叉搜索树（AVL树、红黑树）
也可以用下一章节的Map实现

Map中的key是唯一的，符合集合的特点

用双向链表实现

package com.njf;

public class ListSet<E> implements Set<E>{
    
    private DoublyLinkedList<E> list = new DoublyLinkedList<>();

    @Override
    public int size() {
        return list.size();
    }

    @Override
    public boolean isEmpty() {
        return list.isEmpty();
    }

    @Override
    public void clear() {
        list.clear();
    }

    @Override
    public boolean contains(E element) {
        return list.contains(element);
    }

    @Override
    public void add(E element) {
        int index = list.indexOf(element);
        if (index != list.ELEMENT_NOT_FOUND) {
            list.set(index, element);
        }else {
            list.add(element);
        }
    }

    @Override
    public void remove(E element) {
        int index = list.indexOf(element);
        if (index != list.ELEMENT_NOT_FOUND) {
            list.remove(index);
        }
    }

    @Override
    public void traversal(Visitor<E> visitor) {
        if (visitor == null) return;
        int size = list.size();
        for (int i = 0; i < size; i++) {
            if(visitor.visit(list.get(i))) return;
        }
    }
}

代码调用

package com.njf;

import com.njf.Set.Visitor;

public class Main {
    static void test1() {
        Set<Integer> listSet = new ListSet<>();
        listSet.add(10);
        listSet.add(11);
        listSet.add(11);
        listSet.add(12);
        listSet.add(10);
        listSet.traversal(new Visitor<Integer>() {
            @Override
            public boolean visit(Integer element) {
                System.out.println(element);
                return false;
            }
        });
    }
    public static void main(String[] args) {
        test1();
    }
}

打印结果：

10
11
12

用红黑树实现

package com.njf;

import java.util.Comparator;

public class TreeSet<E> implements Set<E> {
    
    private RBTree<E> rb;
    
    public TreeSet() {
        this(null);
    }
    
    public TreeSet(Comparator<E> comparator) {
        rb = new RBTree<>(comparator);
    }

    @Override
    public int size() {
        return rb.size;
    }

    @Override
    public boolean isEmpty() {
        return rb.isEmpty();
    }

    @Override
    public void clear() {
        rb.clear();
    }

    @Override
    public boolean contains(E element) {
        return rb.contains(element);
    }

    @Override
    public void add(E element) {
        rb.add(element);
    }

    @Override
    public void remove(E element) {
        rb.remove(element); 
    }

    @Override
    public void traversal(Visitor<E> visitor) {
        rb.inorder(new BinaryTree.Visitor<E>() {
            @Override
            public boolean visit(E element) {
                return visitor.visit(element);
            }
        });
    }
}

代码调用:

package com.njf;

import com.njf.Set.Visitor;

public class Main {
    static void test2() {
        Set<Integer> treeSet = new TreeSet<>();
        treeSet.add(12);
        treeSet.add(10);
        treeSet.add(7);
        treeSet.add(11);
        treeSet.add(10);
        treeSet.add(11);
        treeSet.add(9);
        
        treeSet.traversal(new Visitor<Integer>() {
            @Override
            public boolean visit(Integer element) {
                System.out.println(element);
                return false;
            }
        });
    }

    public static void main(String[] args) {
        test1();
    }
}

打印结果：

7
9
10
11
12

红黑树的实现，元素必须具备可比较性

Map实现

package com.njf;

public class MapSet<E> implements Set<E> {

    private Map<E, Object> map = new TreeMap<>();
    
    @Override
    public int size() {
        return map.size();
    }

    @Override
    public boolean isEmpty() {
        return map.isEmpty();
    }

    @Override
    public void clear() {
        map.clear();
    }

    @Override
    public boolean contains(E element) {
        return map.containsKey(element);
    }

    @Override
    public void add(E element) {
        map.put(element, null);
    }

    @Override
    public void remove(E element) {
        map.remove(element);
    }

    @Override
    public void traversal(Visitor<E> visitor) {
        map.traversal(new Map.Visitor<E, Object>() {
            @Override
            public boolean visit(E key, Object value) {
                return visitor.visit(key);
            }
        });
    }
}