数据结构与算法第六版-Map

大家都知道Map的内部存储实际上是一键值对，下面是书中介绍的map类图，我们可以看到map接口作为定级接口，

 可以看到map作为定级接口，AbstracMap次之， map接口和AbstracMap定义了一些基本的方法，我们将这几两个基本的类定义完成之后，我们来实现下UnsortedTableMap，UnsortedTableMap 实现起来比较简单，因为我们使用arrayList来存储entry，而且还是无序的，当我们坐get,put,remove其实我们都需要一个操作，就是找到entry的位置，所以我们定义了一个方法叫做，findIndex ,剩下的就比较简单了，通过findIndex 找到entry在集合中的位置，然后添加，删除，查找

首先定义map接口

**
 * 

 *
 * @author <[email protected]>
 * @since 2018/9/1116:54
 **/
public interface Map {
    int size();
    boolean isEmpty();
    V get(K k);
    V put(K k, V v);
    Iterable keySet();
    Iterable values();
    Iterable> entrySet();
}

其次就是抽象类

package com.wangyadong.hobby.schedule.jobtask.map;

import com.wangyadong.hobby.schedule.jobtask.tree.pq.Entry;

import java.util.Iterator;

public abstract class AbstractMap implements Map {
    public boolean isEmpty() {
        return size() == 0;
    }
    //---------------- nested MapEntry class ----------------
    protected static class MapEntry implements Entry {
        private K k; // key
        private V v; // value
        public MapEntry(K key, V value) {
            k = key;
            v = value;
        }
        // public methods of the Entry interface
        public K getKey() {
            return k;
        }
        public V getValue() {
            return v;
        }
        // utilities not exposed as part of the Entry interface
        protected void setKey(K key) {
            k = key;
        }
        protected V setValue(V value) {
            V old = v;
            v = value;
            return old;
        }
    } //----------- end of nested MapEntry class -----------
    // Support for public keySet method...
    private class KeyIterator implements Iterator {
        private Iterator> entries = entrySet().iterator(); // reuse entrySet
        public boolean hasNext() {
            return entries.hasNext();
        }
        public K next() {
            return entries.next().getKey();
        } // return key!
        public void remove() {
            throw new UnsupportedOperationException();
        }
    }
    private class KeyIterable implements Iterable {
        public Iterator iterator() {
            return new KeyIterator();
        }
    }
    public Iterable keySet() {
        return new KeyIterable();
    }
    // Support for public values method...
    private class ValueIterator implements Iterator {
        private Iterator> entries = entrySet().iterator(); // reuse entrySet
        public boolean hasNext() {
            return entries.hasNext();
        }
        public V next() {
            return entries.next().getValue();
        } // return value!
        public void remove() {
            throw new UnsupportedOperationException();
        }
    }
    private class ValueIterable implements Iterable {
        public Iterator iterator() {
            return new ValueIterator();
        }
    }
    public Iterable values() {
        return new ValueIterable();
    }
}

最终我们的UnsortedTableMap

package com.wangyadong.hobby.schedule.jobtask.map;

import com.wangyadong.hobby.schedule.jobtask.tree.pq.Entry;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.NoSuchElementException;

public class UnsortedTableMap extends AbstractMap {
    /**
     * Underlying storage for the map of entries.
     **/
    private ArrayList> table = new ArrayList<>();

    /**
     * ∗ Constructs an initially empty map. ∗
     **/
    public UnsortedTableMap() {
    }


    /**
     * ∗Returns the index of an entry with equal key, or −1 if none found.
     **/
    private int findIndex(K key) {
        int n = table.size();
        for (int j = 0; j < n; j++)
            if (table.get(j).getKey().equals(key))
                return j;
        return -1;
        // special value denotes that key was not found
    }

    /**
     * Returns the number of entries in the map.
     **/
    public int size() {
        return table.size();
    }

    /**
     * ∗ Returns the value associated with the specified key (or else null).
     **/
    public V get(K key) {
        int j = findIndex(key);
        if (j == -1) return null; // not found
        return table.get(j).getValue();
    }

    /**
     * ∗Associates given value with given key, replacing a previous value (if any).
     **/
    public V put(K key, V value) {
        int j = findIndex(key);
        if (j == -1) {
            table.add(new MapEntry<>(key, value)); // add new entry
            return null;
        } else // key already exists
            return table.get(j).setValue(value); // replaced value is returned
    }

    /**
     * Removes the entry with the specified key (if any) and returns its value. /
     **/
    public V remove(K key) {
        int j = findIndex(key);
        int n = size();
        if (j == -1) return null; // not found
        V answer = table.get(j).getValue();
        if (j != n - 1)
            table.set(j, table.get(n - 1)); // relocate last entry to ’hole’ created by removal
        table.remove(n - 1); // remove last entry of table
        return answer;
    }

    // Support for public entrySet method...
    private class EntryIterator implements Iterator> {
        private int j = 0;

        public boolean hasNext() {
            return j < table.size();
        }

        public Entry next() {
            if (j == table.size()) throw new NoSuchElementException();
            return table.get(j++);

        }

        public void remove() {
            throw new UnsupportedOperationException();
        }
    }

    private class EntryIterable implements Iterable> {
        public Iterator> iterator() {
            return new EntryIterator();
        }
    }
    //** Returns an iterable collection of all key-value entries of the map. **/


    public Iterable> entrySet() {
        return new EntryIterable();
    }

    public static void main(String[] args) {
        UnsortedTableMap map = new UnsortedTableMap();
        map.put("a", "1");
        map.put("b", "2");
        map.put("c", "3");
        map.put("d", "4");
        map.remove("a");
    }
}