Java系列：Collection.toArray用法研究

該方法的簽名如下：

<T> T[] Collection.toArray(T[] arrayToFill);

這里想驗證兩個問題：

1）arrayToFill什么時候會被填充；

2）arrayToFill和返回值是否是同一個值？

測試代碼如下。

static void testToArray(){        
        LinkedList<String> strList = new LinkedList<String>();
        strList.add("zhang.san");
        strList.add("li.si");
        strList.add("wang.wu");
        print("filled array is not large enough.");
        testToArrayHelper(strList, new String[2]);
        
        print("filled array is large enough.");
        testToArrayHelper(strList, new String[3]);
    }
static void testToArrayHelper(LinkedList<String> strList, String[] filledArray){        
        String[] returnedArray = strList.toArray(filledArray);
        printArray("filled array:", filledArray);
        print("");
        printArray("returned array:", returnedArray);
        print("");
        if(filledArray == returnedArray)
            print("filled array is equal returned array.");
        else
            print("filled array is not equal returned array.");
    }
static <T> void printArray(String title, T[] array){
        print(title);
        for(T item: array){
            if(item != null)
                print("item:" + item.toString());
            else
                print("item is null");
        }
    }
static void print(String info){
        System.out.println(info);
    }

輸出日志如下：

filled array is not large enough.
filled array:
item is null
item is null
returned array:
item:zhang.san
item:li.si
item:wang.wu
filled array is not equal returned array.

filled array is large enough.
filled array:
item:zhang.san
item:li.si
item:wang.wu
returned array:
item:zhang.san
item:li.si
item:wang.wu
filled array is equal returned array.

結論，

1）如果arrayToFill的長度如果小於Collection的長度，則不會填充；

2）當arrayToFill被填充的時候，他和返回值其實是同一個數組；