Question

除了一个元素外，我如何从数组列表中选择随机元素？这是我的arraylist：

ArrayList <String> provinces = new ArrayList();

Collections.addAll(
    provinces, 
    "New Brunswick", 
    "Saskatchewan", 
    "Ontario", 
    "Nova Scotia", 
    "Quebec", 
    "Alberta");

对于这个例子，我想随机选择其他元素，除了萨斯喀彻温省。

我尝试过：

 for(int i == provinces.get (0); i < provinces.get(1); i > provinces.get(2); i < provinces.get(5)) {

     int getPossibleAnswers = (int) Math.floor(Math.random()*i);               
     String displayPossibleAnswers = provinces.get(getPossibleAnswers);                
     outputAnswers.append(displayPossibleAnswers + "\n");
     }

显然，这段代码不起作用，我不知道该怎么做。提前致谢！

Answer 1

构建所有索引值的列表，除了Saskatchewan的索引，然后将其洗牌。

List<String> provinces = Arrays.asList("New Brunswick", "Saskatchewan", "Ontario", "Nova Scotia", "Quebec", "Alberta");

List<Integer> indexes = new ArrayList<>();
for (int i = 0; i < provinces.size(); i++)
    if (! provinces.get(i).equals("Saskatchewan"))
        indexes.add(i);
Collections.shuffle(indexes);

StringBuilder outputAnswers = new StringBuilder();
for (int i : indexes)
    outputAnswers.append(provinces.get(i) + "\n");

System.out.print(outputAnswers);

示例输出

Nova Scotia
Quebec
Ontario
Alberta
New Brunswick

Answer 2

为简明扼要，作为mentioned只需创建list而不Saskatchewan

    ArrayList <String> provinces = new ArrayList<>(Arrays.asList("New Brunswick",
                                     "Ontario", "Nova Scotia",
                                     "Quebec",   "Alberta"));

然后随机播放list

Collections.shuffle(provinces);

演示

ArrayList <String> provinces = new ArrayList<>(Arrays.asList("New Brunswick",
                                     "Ontario", "Nova Scotia",
                                     "Quebec",   "Alberta"));
Collections.shuffle(provinces);
StringBuilder builder = new StringBuilder();
for (String s:provinces) {
    builder.append(s+"\n");
}
System.out.println(builder);

输出：

Quebec
New Brunswick
Alberta
Ontario
Nova Scotia

Answer 3

ArrayList <String> provinces = new ArrayList<>();
String removeValue = null;
Collections.addAll(
    provinces, 
    "New Brunswick", 
    "Saskatchewan", 
    "Ontario", 
    "Nova Scotia", 
    "Quebec", 
    "Alberta");

for (Iterator<String> iterator = provinces.iterator(); iterator.hasNext(); ) {
    String value = iterator.next();
    if (value.equals("Saskatchewan")) {
        removeValue = value;
        iterator.remove();
    }
}

Collections.shuffle(provinces);

for(String p: provinces){
    System.out.println(p);
}

provinces.add(removeValue);

我使用了Iterator，因为增强型for循环不适用于remove()但没有Iterator，您也可以使用索引（数字）循环。

没有Iterator：

for (int j = 0; j<provinces.size(); j++) {
    if(provinces.get(j).equals("Saskatchewan")){
        removeValue = provinces.get(j);
        provinces.remove(provinces.get(j));
    }
}

也可以不使用Collections.shuffle()创建自己的方法。要做到这一点，请查看this question。

Answer 4

如果您经常需要随机化（例如，对于随机测试），您可以添加Qala Datagen依赖项，然后获取这样的随机元素：

String e = sample(provinces);

虽然你仍然需要从集合中删除额外的元素。

免责声明：我是lib的作者。

从arraylist中选择多个/随机元素

4 个答案: