创建数字数组不循环？ [英] Creating an array of numbers without looping?

问题描述

好了，所以我使用JavaMail库，我试图获取某些消息编号。我想这样做有效，不必过度东西两次循环...反正我对你的问题是：如何创建开始于指数 X ，并在指数结束数组 X - 11 不用循环

解决方案

如果你想创建和填充一个数组，你基本上有三种选择：

1. 明确写值： INT [] = NUM​​S新INT [] {0，1，2，3，4，...}




2. 使用某种形式的for循环：的for（int i = 0;我小于10;我++）{NUMS [我] =我; }




3. 递归创建它：

INT [] = NUM​​S新INT [12];
NUMS =填充（0，X，NUMS）;私人诠释[]填充（INT指数，诠释的x，INT [] NUMS）{
    如果（nums.length> =指数）{
        返回NUMS;
    }其他{
        NUMS [指数] = X  - 指数; //的x 0到x-11
        返回填充（指数+1，X，NUMS）;
    }
}

香草的Java，没有额外的库和诸如此类的东西，不支持地图功能将允许你指定一个函数，会以某种方式自动生成你的价值观。

不过，我真的不明白，为什么你不希望使用一个循环，尤其是对于像这样的一些小事。

Okay so I am using the JavaMail library and I am trying to fetch certain message numbers. I want to do it efficiently and not have to loop twice over something… Anyways my question to you is: How can I create an array that starts at index x and ends at index x - 11 without looping?

解决方案

If you want to create and populate an array, you have basically three options:

1. Write the values explicitly: int[] nums = new int[] { 0, 1, 2, 3, 4, ... }

2. Use some form of for-loop: for (int i = 0; i < 10; i++) { nums[i] = i; }

3. Create it recursively:

int[] nums = new int[12];
nums = populate(0, x, nums);

private int[] populate(int index, int x, int[] nums) {
    if (nums.length >= index) {
        return nums;
    } else {
        nums[index] = x - index; // x-0 through x-11
        return populate(index+1, x, nums);
    }
}

Vanilla Java, without extra libraries and whatnot, doesn't support a map function which would allow you to specify a function that would somehow auto-generate your values.

Though, I really don't understand why you don't want to use a loop, especially for something trivial like this.

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