java - ArrayList 中的问题

Question

import java.util.*;
import java.util.Random;

class ArraySorting {
public static void main(String[]args) {

    ArrayList<Integer> arr = new ArrayList<Integer>();

    Random generate = new Random();
    for (int nums = 0; nums < 20; nums++) {
      int randomnumbers = generate.nextInt(50);
      arr.add(randomnumbers);
    }

    System.out.println("First list of 20 generated numbers: ");
    System.out.println(arr);
    System.out.println("");

    int dupe = 0; 

    for (int n = 0; n < arr.size(); n++) {
        Integer check1 = arr.get(n); 

        for (int n2 = n+1; n2 < arr.size(); n2++) { 
            Integer check2 = arr.get(n2); 

            //remove second num if two numbers akike
            if (check1.equals(check2)) {
                arr.remove(check2);
                n2 = n2-1;
                dupe = 1; 

            }
        }
        n = n-dupe;
        dupe = 0;
    }

    System.out.println("Duplicates: " + (20 - arr.size()));

    for (int n3 = arr.size(); n3 < 20; ++n3) {
        int randomnumbers = generate.nextInt(50);
        arr.add(randomnumbers);

        //check for duplicates again
        for (int n = 0; n < arr.size(); n++) {
            Integer check1 = arr.get(n); 

            for (int n2 = n+1; n2 < arr.size(); n2++) { 
                Integer check2 = arr.get(n2); 

                if (check1.equals(check2)) {
                    arr.remove(check2);
                    n2 = n2-1;
                    dupe = 1; 
                }
            }
            n = n - dupe;
            dupe = 0;
        }
    }

    //before sort
    System.out.println(arr);
    System.out.println("");

    for(int a=0; a<20; a++){
        for (int b = 0; b < 19; b++) {
            if(arr[b] > arr[b+1]){
                int temporary = arr[b];
                arr[b] = arr[b+1];
                arr[b+1] = temporary;
            }
        }
    }

    System.out.println("\nSorted Array:\n");
    for (int a = 0; a < 20; a++) {
        System.out.println("Array [" + a + "]: " + arr[a]);
    }


}

}

谁能告诉我我做错了什么，我似乎无法生成最后一部分。不应该 ArrayList arr = new ArrayList();与 arr[b] 工作的最后一部分运行相同？我是 Java 的新手，所以如果在解决方案中提供简单的解释/隐喻，我将不胜感激。

P.S:我不打算使用像Collection这样的库排序函数，我需要在最后一部分使用排序方法。

Answer 1

arr[a] 是访问数组元素的语法。对于 ArrayList，您使用 arr.get(a)。要为 ArrayList 赋值，您可以使用 arr.set(b,value)。您不能使用赋值运算符。