一、背景：　　　　　　　　　　

package com.cy.collection;

public class Wife {
    String name;
    
    public Wife(String name){
        this.name = name;
    }

    @Override
    public String toString() {
        return "Wife [name=" + name + "]";
    }
}
 

Map.java:

package com.cy.collection;

/**
 * 自定義實現Map
 */
public class Map {
    private Entry[] arr = new Entry[1000];    //這裏暫時不考慮擴容
    private int size;                        //這裏都是private的，不暴露size屬性
    
    /**
     * 1.鍵不能重復,如果含有這個鍵，就替換value
     * @param key
     * @param value
     */
    public
 
 void put(Object key, Object value){
        for(int i=0; i<size; i++){
            if(arr[i].key.equals(key)){
                arr[i].value = value;
                return;
            }
        }
        arr[size++] = new Entry(key, value);
    }
    
    //根據key獲取
    public Object get(Object key){
        
 
for(int i=0; i<size; i++){
            if(arr[i].key.equals(key)){
                return arr[i].value;
            }
        }
        return null;
    }
    
    //根據key刪除
    public boolean remove(Object key){
        boolean success = false;
        for(int i=0;i<size;i++){
            if(arr[i].key.equals(key)){
                success = true;
                remove(i);
            }
        }
        return success;
    }
    private void remove(int i){
        int numMoved = size - i - 1;
        if(numMoved>0){
            System.arraycopy(arr, i+1, arr, i, numMoved);
        }
        arr[--size] = null;        //Let gc do its work
    }
    
    //containsKey
    public boolean containsKey(Object key){
        for(int i=0; i<size; i++){
            if(arr[i].key.equals(key)){
                return true;
            }
        }
        return false;
    }
    
    //containsValue 同containsKey
    
    //size
    public int size(){
        return size;
    }
}

/**
 * 用來存放鍵值對的條目
 */
class Entry{
    Object key;
    Object value;
    
    public Entry(Object key, Object value) {
        super();
        this.key = key;
        this.value = value;
    }
}

Test.java測試代碼：

package com.cy.collection;

public class Test {

    public static void main(String[] args) {
        Map map = new Map();
        map.put("張三", new Wife("abc"));
        map.put("李四", new Wife("def"));
        map.put("王五", new Wife("ghi"));
        System.out.println(map.get("張三"));
        map.remove("李四");
        System.out.println(map.size());
        
        map.put("張三", new Wife("aaa"));
        System.out.println(map.get("張三"));
        System.out.println(map.containsKey("張三"));
    }

}

輸出：
Wife [name=abc]
2
Wife [name=aaa]
true

HashMap的自定義實現