Lists.newArrayListWithExpectedSize( int estimatedSize)

Lists.newArrayListWithExpectedSize( int estimatedSize)  構造一個期望長度為estimatedSize的ArrayList實例。

源碼：

 

public static <E> ArrayList<E> newArrayListWithExpectedSize(int estimatedSize) {
    return new ArrayList(computeArrayListCapacity(estimatedSize));
}

 

//計算集合的容量
@VisibleForTesting
static int computeArrayListCapacity(int arraySize) {
//判斷是否小於0，小於0則拋出異常。
    CollectPreconditions.checkNonnegative(arraySize, "arraySize");
    return Ints.saturatedCast(5L + (long)arraySize + (long)(arraySize / 10));
}

//檢查是否小於0
@CanIgnoreReturnValue
static int checkNonnegative(int value, String name) {
    if (value < 0) {
        throw new IllegalArgumentException(name + " cannot be negative but was: " + value);
    } else {
        return value;
    }
}

//判斷計算出來的數組長度是否在int的范圍內
public static int saturatedCast(long value) {
    if (value > 2147483647L) {
        return 2147483647;
    } else {
        return value < -2147483648L ? -2147483648 : (int)value;
    }
}