创建一个从 0 到 9 的整数列表，将其打乱并提取前 4 个.

Create a list of integers from 0 to 9, shuffle it and extract the first 4.

public static void main(String[] args) {
    List<Integer> numbers = new ArrayList<>();
    for(int i = 0; i < 10; i++){
        numbers.add(i);
    }

    Collections.shuffle(numbers);

    String result = "";
    for(int i = 0; i < 4; i++){
        result += numbers.get(i).toString();
    }
    System.out.println(result);
}

正在进行一些丑陋的字符串到整数的转换，但你明白了.根据您的用例，您可以看到需要什么.

There's some ugly string-to-int conversing going on, but you get the idea. Depending on your use case you can see what is needed.