JS自定义对象实现Java中Map对象功能的方法

/**
 * @version 1.0 
 * 用于实现页面 Map 对象，Key只能是String，对象随意
 */ 
var Map = function(){ 
    this._entrys = new Array(); 
     
    this.put = function(key, value){ 
        if (key == null || key == undefined) { 
            return; 
        } 
        var index = this._getIndex(key); 
        if (index == -1) { 
            var entry = new Object(); 
            entry.key = key; 
            entry.value = value; 
            this._entrys[this._entrys.length] = entry; 
        }else{ 
            this._entrys[index].value = value; 
        }         
    }; 
    this.get = function(key){ 
        var index = this._getIndex(key); 
        return (index != -1) ? this._entrys[index].value : null; 
    }; 
    this.remove = function(key){ 
        var index = this._getIndex(key); 
        if (index != -1) { 
            this._entrys.splice(index, 1); 
        } 
    }; 
    this.clear = function(){ 
        this._entrys.length = 0;; 
    }; 
    this.contains = function(key){ 
        var index = this._getIndex(key); 
        return (index != -1) ? true : false; 
    }; 
    this.getCount = function(){ 
        return this._entrys.length; 
    }; 
    this.getEntrys =  function(){ 
        return this._entrys; 
    }; 
   this._getIndex = function(key){ 
        if (key == null || key == undefined) { 
            return -1; 
        } 
        var _length = this._entrys.length; 
        for (var i = 0; i < _length; i++) { 
            var entry = this._entrys[i]; 
            if (entry == null || entry == undefined) { 
                continue; 
            } 
            if (entry.key === key) {//equal 
                return i; 
            } 
        } 
        return -1; 
    }; 
}

// 自定义Map对象 
var map = new Map(); 
map.put("a","a"); 
alert(map.get("a")); 
map.put("a","b"); 
alert(map.get("a"));