java如何重新排列数组，使空值占据数组的开头？

Question

我不知道如何将null元素添加到数组的前面

有没有办法在不反转阵列的情况下执行此操作？也许是一种具体的方法

public static void main(String[] args) {
    String[] stringArray = new String[]{"one", "two", "three"};
    method(stringArray);
}

public static String[] method(String[] stringArray) {
    String[] biggerStringArray = Arrays.copyOf(stringArray, stringArray.length * 2);

    for (int i = 0; i < biggerStringArray.length; i++) {
        System.out.print(biggerStringArray[i] + ", ");

    }

    return biggerStringArray;
}

我希望结果如下所示：

null, null, null, one, two, three,

而不是：

one, two, three, null, null, null

Answer 1

首先可以创建一个长度等于stringArray的空数组。然后可以使用任何Java数组连接方法将stringArray连接到新的空数组

这里有一个例子

public static String[] method(String[] stringArray) {
    String[] nullArray = new String[stringArray.length];
    String[] biggerStringArray = Stream.of(nullArray, stringArray).flatMap(Stream::of).toArray(String[]::new);

    // for (int i = 0; i < biggerStringArray.length; i++) {
    //     System.out.print(biggerStringArray[i] + ", ");
    // }

    return biggerStringArray;
}

Answer 2

public static void main(String[] args) {
    String[] stringArray = new String[] {"one", "two", "three"};
    method(stringArray);
  }

  public static String[] method(String[] stringArray) {
    String[] biggerStringArray = new String[stringArray.length * 2];

    for (int i = 0; i < stringArray.length; i++) {
      biggerStringArray[i + biggerStringArray.length / 2] = stringArray[i];
    }

    for (int i = 0; i < biggerStringArray.length; i++) {
      System.out.print(biggerStringArray[i] + ", ");
    }
    return biggerStringArray;
  }

编辑：刚刚记住你也可以使用System.arraycopy：

public static String[] method(String[] stringArray) {
    String[] biggerStringArray = new String[stringArray.length * 2];

    System.arraycopy(stringArray, 0, biggerStringArray, biggerStringArray.length / 2, stringArray.length);

    for (int i = 0; i < biggerStringArray.length; i++) {
      System.out.print(biggerStringArray[i] + ", ");
    }
    return biggerStringArray;
  }

Answer 3

据我所知，一个能满足你所需的语句是不存在的。但这并不意味着你不能自己做。有很多方法可以交换数组中的元素。这里有一个：

String[] biggerStringArray = Arrays.copyOf(stringArray, stringArray.length * 2);
for(int i = 0; i < stringArray.length; i++)
{
    biggerStringArray[i] = biggerStringArray[i + stringArray.length];
    biggerStringArray[i + stringArray.length] = null;
}

Answer 4

public static String[] method(String[]stringArray) {
    String[] biggerStringArray = Arrays.copyOf(stringArray, stringArray.length * 2);

    List<String> biggerStringList = Arrays.asList(biggerStringArray);
    biggerStringList.sort(Comparator.nullsFirst(String::compareTo));

    System.out.println(biggerStringList);

    return biggerStringList.toArray(new String[biggerStringList.size()]);
}

Answer 5

您可以编写自己的copy方法，如下所示

    public static String[] copyArray(String[] array, int length) {
        String[] biggerStringArray = new String[length];
        for (int i = 1; i <= array.length; i++) {
            biggerStringArray[biggerStringArray.length - i] = array[array.length - i];
        }
        return biggerStringArray;
    }