从 ArrayList HashMap 获取多个随机值 [英] get multiple random values from ArrayList HashMap

问题描述

我想从 ArrayList 中获取一些特定数字的随机值

I want to get some specific number random values from ArrayList

final ArrayList<HashMap<String, String>> menuItems = new ArrayList<HashMap<String, String>>();

for (int i = 0; i == 4; i++) {

        index = random.nextInt(menuItems.size());
        HashMap<String, String> getitem = menuItems.get(index);
        System.out.println(getitem.get(KEY_NAME));
    }

什么都没有打印出来.

如果我在循环外使用它，循环中的代码可以工作，但是由于我需要多个值，我使用循环并且它不起作用.

Code in loop works if i use it outside loop, but since i need multiple values, i use loop and it doesnt work.

推荐答案

change

for (int i = 0; i == 4; i++) { // start with i beeing 0, execute while i is 4
                               // never true

到

for (int i = 0; i < 4; i++) {  // start with i beeing 0, execute while i is
                               // smaller than 4, true 4 times

说明:

for 循环具有以下结构:

Explanation:

A for loop has the following structure:

for (initialization; condition; update)

initialization 在循环开始前执行一次.condition 在循环的每次迭代前检查，update 在每次迭代后执行.

initialization is executed once before the loop starts. condition is checked before each iteration of the loop and update is executed after every iteration.

您的初始化是 int i = 0;(执行一次).您的条件是 i == 4，这是错误的，因为 i 是 0.所以条件为假，跳过循环.

Your initialization was int i = 0; (executed once). Your condition was i == 4, which is false, because i is 0. So the condition is false, and the loop is skipped.

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